Imagine having a brain tumor removed while you're completely asleep.

You cannot speak, move your hands, or tell your surgeon whether something feels different. So how can the surgical team know whether the operation is approaching an area of the brain responsible for movement?

The answer is that your nervous system can communicate even when you're unconscious.

Using electrical stimulation and sophisticated monitoring equipment, surgeons can test specific pathways in the brain and spinal cord during an operation. These techniques help identify critical structures, monitor their function, and guide decisions about how much tumor can safely be removed.

This is called asleep brain mapping, and it is an important part of modern brain tumor surgery.

Your Brain Is an Electrical Network

Every time you move your hand, wiggle your toes, or take a step, electrical signals travel through a complex network of neurons.

The process begins in regions of the brain involved in planning and initiating movement. Signals travel through the motor cortex, descend along white matter pathways, pass through the brainstem, and ultimately reach the spinal cord and muscles.

One of the most important pathways is the corticospinal tract.

Think of it as a major communication highway connecting the brain to the body.

Damage to this pathway can cause weakness or paralysis, even when the part of the brain responsible for initiating movement remains intact.

This distinction is especially important in brain tumor surgery.

A tumor may be located far from the surface of the brain, yet still lie immediately adjacent to the white matter pathways that control movement.

Protecting these connections can be just as important as protecting the brain's outer surface.

How Do Surgeons Test Movement When You're Asleep?

During surgery, specialized electrodes can stimulate parts of the nervous system while other electrodes record the resulting electrical activity.

Two techniques are particularly important.

1. Motor Evoked Potentials: Monitoring the Movement Pathways

Motor evoked potentials, or MEPs, help surgeons assess whether signals can travel from the brain to the muscles.

Electrical stimulation is delivered to the motor system, and electrodes placed in muscles record the resulting responses.

If those responses change significantly during surgery, the team investigates whether the motor pathways may be under stress.

This can happen because of mechanical manipulation, changes in blood supply, or other physiological factors.

Importantly, a change in an MEP does not automatically mean permanent injury has occurred.

It is a warning signal that must be interpreted in context.

The surgical team may pause, adjust its technique, optimize physiological conditions, or reassess the operative strategy.

The goal is to identify potentially reversible problems before they become lasting neurological deficits.

2. Direct Electrical Stimulation: Finding the Boundaries

Monitoring tells us whether a pathway is functioning.

Direct electrical stimulation helps us identify where that pathway is located.

During surgery, a surgeon can apply small electrical currents directly to brain tissue using a specialized probe.

When stimulation activates motor-related structures, the team may detect a response in the patient's muscles.

This allows the surgeon to identify functional tissue and pathways even when the patient is under general anesthesia.

For example, while removing a tumor deep within the frontal lobe, stimulation of tissue near the surgical cavity may produce a response in the hand or leg.

That information helps the surgeon understand the relationship between the tumor and the patient's motor pathways.

As the operation progresses, repeated stimulation can help define the functional boundaries of the resection.

The exact interpretation depends on the stimulation technique, anesthesia, anatomy, and other factors. Electrical responses are not a perfect measurement of distance or safety.

But they provide valuable information that anatomical imaging alone cannot.

What About Sensation?

Movement is only one part of neurological function.

The brain also receives a continuous stream of sensory information from the body.

Surgeons can monitor some of these pathways using somatosensory evoked potentials, or SSEPs.

Small electrical impulses are delivered to peripheral nerves, commonly at the wrist or ankle. The resulting signals are recorded as they travel through the nervous system.

Changes in these responses may indicate that sensory pathways are being affected.

SSEPs can also help identify the central sulcus, an important anatomical boundary separating the primary motor and sensory cortices.

Together, MEPs, SSEPs, and direct electrical stimulation provide complementary information.

One technique cannot replace all the others.

Brain Mapping Is More Than Watching a Screen

Modern brain tumor surgery often begins long before the patient enters the operating room.

Preoperative MRI can identify the tumor and surrounding anatomy.

Diffusion MRI tractography can estimate the location of major white matter pathways.

Functional imaging and connectomics may provide additional information about how the tumor interacts with broader brain networks.

These tools help surgeons develop a plan.

But there is an important limitation.

A brain map created before surgery is not the same as a functional measurement obtained during surgery.

As tissue is removed, the brain can shift. The relationship between the tumor and surrounding structures can change.

And tractography, while valuable, is a computational estimate rather than a direct demonstration of whether a pathway is functioning.

This is why intraoperative mapping remains important.

Preoperative imaging provides the roadmap. Intraoperative stimulation and monitoring help test that roadmap against the patient's actual physiology.

Does Everyone Need to Be Awake for Brain Tumor Surgery?

No!

Awake brain surgery can be particularly valuable when surgeons need to test complex functions such as speech, language, or certain cognitive abilities.

These functions often require the patient to actively participate in testing.

But many motor pathways can be assessed under general anesthesia.

For some tumors, asleep mapping provides the information needed to guide a safe resection without requiring the patient to be awake.

In other situations, an awake procedure may offer important advantages.

The decision depends on several factors, including the tumor's location, the neurological functions at risk, the patient's health and preferences, and the capabilities of the surgical team.

Neither approach is universally superior.

The objective is not to perform the most technologically elaborate operation. It is to choose the mapping strategy that best protects the functions that matter to that patient.

Can Mapping Prevent Every Neurological Deficit?

Unfortunately, no.

Brain tumors can distort normal anatomy, infiltrate functioning tissue, and affect the blood vessels supplying critical regions.

Even with advanced monitoring, some injuries cannot be predicted or prevented.

Electrical signals can also remain stable despite certain types of neurological injury.

Furthermore, monitoring motor pathways does not necessarily tell us whether language, memory, attention, or other complex functions will be preserved.

This is one reason modern brain tumor surgery increasingly combines multiple sources of information.

The surgeon must interpret the anatomy, the imaging, the patient's baseline neurological function, the intraoperative findings, and the goals of treatment.

Sometimes the safest decision is to leave a small amount of tumor behind.

That is not necessarily a failure of surgery.

It may represent the best balance between removing disease and preserving the patient's independence and quality of life.

Questions to Ask Your Brain Tumor Surgeon

If you or someone you love is preparing for brain tumor surgery, consider asking:

1. Is my tumor near a pathway responsible for movement, sensation, or language?

2. Will you use electrical stimulation or neurological monitoring during surgery?

3. Would awake or asleep mapping be more appropriate for my tumor?

4. How will you determine when further tumor removal becomes too risky?

5. What neurological changes are possible after surgery, and which may improve with rehabilitation?

These conversations are especially important when a tumor is located near critical functional structures.

The Bottom Line

Brain tumor surgery is not simply about removing abnormal tissue.

It is about understanding which parts of the brain and its connections must continue working after the operation.

Asleep brain mapping allows surgeons to gather functional information from the nervous system while the patient remains under general anesthesia.

Combined with modern imaging, direct electrical stimulation, and careful surgical judgment, these techniques can help guide safer and more individualized operations.

The goal is not merely to remove as much tumor as possible.

It is to remove as much tumor as safely possible while preserving the neurological functions that make everyday life possible.

Frequently Asked Questions

Can surgeons test my brain while I'm unconscious?

Yes. Electrical stimulation and neurophysiological monitoring can assess certain motor and sensory pathways during general anesthesia.

Does brain mapping hurt?

During asleep mapping, the patient is under anesthesia and does not consciously experience the stimulation. Muscle responses can still occur.

Is awake brain surgery always better?

No. Awake and asleep mapping serve different purposes. The appropriate technique depends on the tumor's location and the neurological functions that need to be tested.

Can brain mapping guarantee that I won't have weakness after surgery?

No. Mapping can help identify and monitor important pathways, but it cannot eliminate every risk of neurological injury.

What is the difference between tractography and electrical stimulation?

Tractography estimates the location of white matter pathways using MRI data. Electrical stimulation tests physiological responses during surgery. They provide complementary information.

One of the most important questions in brain tumor surgery is also one of the simplest:

How does the surgeon know where to stop?

Brain mapping is a technique used during brain surgery to identify areas and pathways responsible for important functions such as movement, speech and language, helping surgeons determine what tissue can be safely removed.

MRI can show us where a tumor is. It can show us how big it is. It can show us which structures are nearby.

But MRI alone cannot always tell us exactly what a specific piece of brain tissue is doing in a specific person. That is where brain mapping comes in.

Brain mapping allows us to test brain function during surgery and identify the regions and pathways that matter most for movement, speech, language, vision, attention, and other abilities.

In simple terms: Imaging helps us predict where function may be. Mapping helps us test it.

That distinction can shape how much tumor we can safely remove.

Believe it or not! The brain does not come with labels!

If you open a textbook, the brain looks beautifully organized. Language here. Movement there. Vision in the back. Memory in the temporal lobe.

Real brains are slightly more complicated.

There is enormous consistency in how the nervous system is organized, but there is also meaningful variation from person to person.

Tumors make that even more complicated. A slow-growing tumor can distort anatomy over years. Nearby regions may adapt. Networks may reorganize. White-matter pathways may be displaced rather than destroyed.

So even when we have excellent imaging, the most important question is often not:

“Where should this function be?”

It is:

“Where is this function in this patient?”

Brain mapping starts before the operation

The mapping process does not begin when the surgeon touches the brain. It begins during planning.

Depending on the case, that may include:

• structural MRI

• diffusion imaging and tractography

• functional MRI

• connectomic analysis

• neuropsychological testing

• detailed language or motor assessment

• the neurological examination

These tools help us build a working map of the tumor and the networks around it. But this is still a hypothesis. The operating room is where we can sometimes test that hypothesis directly.

What is direct electrical stimulation?

During brain mapping, a surgeon can apply a very small electrical stimulus to the surface of the brain or to tissue deeper within it.

The stimulation briefly interrupts or activates the function of that area. The effect is temporary. It does not mean the tissue has been damaged. Think of it like briefly interrupting one connection in a complex electrical system to see what changes.

If a patient is naming pictures and stimulation repeatedly causes the same naming error, that location may be important for language.

If stimulation causes a hand or arm to move, we have identified part of the motor system.

If speech suddenly stops while everything else remains intact, we may have found tissue essential for speech production.

These responses help create a functional map in real time.

Mistakes during mapping are useful!

This often surprises patients. During mapping, a temporary mistake can be exactly what we are looking for.

Imagine a patient is repeatedly shown pictures: Dog, Chair, Apple, Umbrella. Then, during stimulation of one small area, the patient suddenly cannot name the umbrella. A few seconds later, stimulation stops and the word comes back.

That is not a failed test. It is valuable information. It tells us that disturbing that region affects a function we are trying to preserve. A temporary error during mapping may help prevent a permanent one after surgery.

Motor mapping

Movement is one of the clearest examples of why mapping matters.

The motor cortex sends signals down through deep white-matter pathways, including the corticospinal tract, before those signals reach the spinal cord and muscles.

During surgery, we may use electrical stimulation to identify:

• the motor cortex

• pathways controlling the face

• pathways controlling the hand

• pathways controlling the leg

• deeper motor fibers beneath the tumor

We may also use neurophysiological monitoring, including motor evoked potentials and sensory signals, to watch those systems continuously. These techniques help us understand how close the operation is getting to structures that could affect strength or movement.

Language mapping is more complicated

Language is not stored in one tiny spot in the brain. It is a network.

Speaking requires multiple processes:

• finding the right word

• understanding meaning

• producing sounds

• sequencing speech

• reading

• repeating

• connecting concepts

• coordinating the muscles involved in speech

That is why language mapping may involve several different tasks. During surgery, a patient might:

• name pictures

• read words

• repeat sentences

• count

• describe images

• complete phrases

• answer simple questions

The exact tasks depend on where the tumor is and which language networks may be at risk. A tumor near speech production pathways requires different testing than one near semantic or reading networks.

Cortical mapping versus subcortical mapping

This distinction is especially important.

Cortical mapping

This tests the brain's surface. It helps identify areas of cortex involved in functions such as movement or language. But removing a tumor is rarely only about the surface. Many gliomas extend deeper into the brain.

That is where white matter becomes critical…

Subcortical mapping

As surgery progresses deeper, stimulation can be used to test the pathways beneath the cortex. These white-matter tracts are the brain's communication cables. They connect distant regions into functioning networks.

Examples include pathways involved in:

• movement

• language

• vision

• attention

• speech initiation

• semantic processing

This is one of the reasons I think of modern brain surgery less as removing a mass and more as navigating a network.

Why white matter matters so much

Cortex gets much of the attention because it is easy to visualize. But white-matter pathways may be even less forgiving. A portion of cortex may sometimes be compensated for by neighboring regions. A major communication highway can be much harder to replace.

That means a surgeon may safely remove tumor through one region, only to reach a deeper boundary where the risk suddenly changes. This is why the last few millimeters of a resection can matter so much. And it is one reason direct subcortical mapping can help determine when the safest decision is to stop.

What about vision, attention, and higher-level cognition?

Brain mapping is evolving beyond traditional motor and language testing. In selected cases, teams may also test functions such as:

• reading

• visual processing

• spatial attention

• executive function

• working memory

• social cognition

These functions are harder to test reliably in the operating room. They often depend on widely distributed networks rather than one isolated region. That makes them one of the most interesting frontiers in functional neurosurgery. The broader lesson is that preserving function means thinking beyond whether a patient can simply move an arm or say their name.

Where does connectomics fit?

Connectomics is the study of how different parts of the brain are connected into networks.

For brain tumor surgery, connectomic imaging can help us understand which large-scale networks may run through or around a tumor. That can be incredibly useful for planning. But imaging and direct mapping serve different purposes.

Connectomics may help answer:

“Where might an important network be?”

Direct stimulation may help answer:

“Does disrupting this specific location actually affect function right now?”

The two approaches can complement each other. One helps build the roadmap. The other can test the road while we are traveling on it.

Is brain mapping always done while the patient is awake?

No. Some mapping can be performed under general anesthesia. Motor pathways, for example, can often be mapped and monitored without the patient being awake.

Language is different. If we need to know whether stimulation affects naming, reading, comprehension, or speech, we need the patient to perform those tasks. That is why certain tumors near important language networks may be approached with awake brain mapping.

The patient does not need to be awake for the entire operation. In many cases, they are asleep for portions of the procedure and awake only during the period when functional testing is needed.

Does mapping make surgery safer?

The goal of mapping is to increase the amount of useful information available during surgery. For appropriately selected tumors, particularly those near critical functional areas, direct mapping can help identify boundaries that would be difficult to determine from anatomy alone.

That can support two equally important goals:

Remove as much tumor as safely possible.

and

Preserve the neurological function that matters to the patient.

Neither goal should exist without the other.

What happens when mapping says “stop”?

This is where brain mapping connects directly to the idea of maximal safe resection. Imagine that most of a tumor has been removed. There is still abnormal tissue visible. But stimulation now repeatedly produces a language error.

Or motor stimulation shows that the corticospinal tract is extremely close. At that point, the remaining tumor may carry a very different risk than what has already been removed. That is not necessarily a failed operation. It may mean we have found the functional boundary. Good surgery is not simply about knowing how to remove tumor. Sometimes it is about knowing when not to.

Can brain mapping be wrong?

No test in medicine is perfect. Mapping results have to be interpreted in context. Fatigue can affect performance. Seizures can interfere with testing. Tumors can distort anatomy. Stimulation parameters matter. Tasks have to be selected carefully. That is why mapping is not a single button or device.

It is a process that combines:

• surgical anatomy

• imaging

• physiology

• patient performance

• neuropsychology

• experience

• judgment

The value comes from putting those pieces together.

What should patients ask their surgeon?

If a tumor is close to an important functional area, reasonable questions include:

Which networks are closest to my tumor?

What functions are most at risk?

Will you use direct brain mapping?

Will I need to be awake for part of the surgery?

Will you use subcortical mapping as well as cortical mapping?

How will you know when it is time to stop removing tumor?

What other tools will you use to protect function?

Those questions often reveal more about the surgical strategy than simply asking how many hours the operation will take.

The bigger picture

Brain tumor surgery has traditionally been described as an anatomical problem: Find the tumor. Expose it. Remove it. But the brain is not simply anatomy. It is a living network. And increasingly, the challenge is not just seeing the tumor more clearly. It is understanding the individual brain around it more clearly.

The future of brain tumor surgery is not simply better tumor visualization. It is better understanding of the person’s functional brain.

And when we can combine imaging, network analysis, direct stimulation, and careful clinical judgment, the goal becomes more precise:

remove what can safely be removed, protect what cannot be replaced, and preserve the life the patient wants to return to.

Frequently Asked Questions

What is brain mapping during brain tumor surgery?

Brain mapping is the process of identifying brain regions and pathways involved in important functions such as movement, speech, and language. It can involve imaging before surgery and direct electrical stimulation during surgery.

Is brain mapping painful?

No. The brain itself does not contain pain receptors. During awake mapping, the scalp is numbed and the anesthesia team focuses on keeping the patient comfortable.

Why do surgeons stimulate the brain?

Electrical stimulation can temporarily alter a specific function, helping surgeons identify areas or pathways that should be preserved.

What is subcortical brain mapping?

Subcortical mapping tests the white-matter pathways beneath the brain's surface. These pathways connect different parts of the brain and may define the functional boundary of a tumor resection.

Do all brain tumor surgeries require mapping?

No. Mapping is most useful when a tumor is near brain regions or pathways where injury could significantly affect neurological function.

Can brain mapping help surgeons remove more tumor?

In selected cases, mapping can provide greater confidence about which tissue can be safely removed while identifying functional boundaries that should be preserved.

Bottom line

Brain mapping helps answer one of the hardest questions in neurosurgery:

Where does safe tumor removal end and unacceptable functional risk begin?

MRI, tractography, connectomics, monitoring, and direct stimulation each provide part of the answer.

Together, they allow brain tumor surgery to become increasingly individualized—not simply to the tumor, but to the person carrying it.

Educational content only and not a substitute for individualized medical advice.

The difference between removing the most tumor and performing the best operation

One of the most understandable questions I hear from patients and families after brain tumor surgery is:

“Why is there still tumor on the MRI?”

It seems intuitive. If a tumor is dangerous, shouldn't the goal of surgery simply be to remove all of it?

For many brain tumors—particularly gliomas—how much tumor we remove matters. Greater extent of resection has repeatedly been associated with better outcomes when it can be accomplished safely.

But there's an important word in that sentence:

Safely.

The goal of modern brain tumor surgery isn't simply maximum resection. It's maximal safe resection.

And understanding the difference explains much of how brain tumor surgeons think in the operating room.

A brain tumor doesn't have to respect the brain's boundaries

Some tumors elsewhere in the body grow more like a ball: tumor here, normal tissue around it. Gliomas are different.

They arise from cells within the brain itself and can infiltrate into the surrounding tissue. Under the microscope, tumor cells may extend beyond what we can clearly see on an MRI.

That creates an immediate problem because there isn't always a clean line that says: TUMOR ENDS HERE! or NORMAL BRAIN HERE!

Instead, the edge can be a transition zone where tumor and functioning brain coexist. That functioning brain may contain the networks responsible for speaking, moving, seeing, reading, remembering, paying attention, or simply being able to live independently.

So the question during surgery isn't: Can I remove more?

It's: Can I remove more without taking away something that matters?

The last 5% may be very different from the first 95%

Imagine a tumor that can largely be removed without encountering an essential brain network. The first portion may come out relatively safely. But as surgery progresses, the anatomy changes. The remaining tumor might approach (see previous stacks for more info on these regions):

• the corticospinal tract, which carries movement signals

• the arcuate fasciculus and other language pathways

• the optic radiations, which carry visual information

• the internal capsule, where enormous amounts of motor and sensory wiring are concentrated

• deep blood vessels that supply normal brain

• networks involved in attention, cognition, memory, or behavior

Suddenly, another few millimeters of tumor removal can carry a very different risk. That's one of the most important concepts for patients to understand:

Every additional percentage of tumor removed does not carry the same benefit-to-risk ratio.

The last 5% may be the most dangerous 5% and it can cause a huge percentage of the problems post-operatively.

What does “maximal safe resection” actually mean?

Maximal safe resection means removing as much tumor as possible while maintaining an acceptable risk to neurological function and quality of life. That balance is different for every patient.

A tumor near the motor pathways of someone who walks for a living raises one set of considerations. A tumor near language networks in a teacher raises another. A tumor affecting visual pathways in someone who already has limited vision may change the calculation again. This is one reason I think brain tumor surgery increasingly needs to move beyond anatomy alone.

We aren't operating on an MRI. We're operating on a person.

Gross total, subtotal, supratotal: what do these terms mean?

Patients frequently encounter these terms in operative reports and MRI results.

Gross-total resection

Generally, this means that all of the tumor visible within the imaging target being used for that particular tumor has been removed. Importantly, gross total does not necessarily mean every tumor cell is gone. Glioma cells can extend microscopically beyond what conventional MRI can see.

Subtotal resection

Some visible tumor remains. Sometimes this is unavoidable. Sometimes it is intentional.

If tumor extends into a critical functional pathway or surrounds important blood vessels, leaving some tumor behind may provide the best balance between tumor control and neurological function.

That isn't necessarily an incomplete operation. Sometimes it is exactly the operation that was planned.

Supratotal or supramaximal resection

This concept is particularly interesting in selected gliomas.

Sometimes the visible MRI abnormality does not represent the true biological boundary of the tumor. If functional mapping shows that surrounding tissue can be safely removed, surgeons may sometimes extend the resection beyond the conventional radiographic tumor margin.

But the principle remains the same. The goal isn't: “Remove more at all costs.” It is: “Remove more when the functional anatomy allows it.”

Biopsy

Sometimes the safest and most useful operation is not a resection at all. A biopsy obtains enough tissue to determine exactly what the tumor is and any molecular information that may determine chemotherapy, radiation, targeted therapy, or clinical-trial options.

For tumors embedded within particularly high-risk structures, obtaining the diagnosis without causing a neurological deficit may be the best surgical result. Sometimes this can be combined with Laser Ablation for a cytoreductive option when carefully planed.

When leaving tumor behind is a decision.

This distinction between a decision and a complication matters. Imagine that during surgery we are approaching the pathway responsible for moving someone's hand. The patient may still be moving normally. The monitoring may still look normal. But stimulation tells us that the motor pathway is now only a few millimeters away. We have learned something extremely valuable. We have found the functional boundary of the operation.

Continuing simply because tumor remains on the MRI could transform a successful tumor operation into a permanent disability. Stopping can be the more sophisticated decision.

But stopping too early matters, too

There is an equally important other side to this discussion. We should not use the importance of neurological function as an excuse for unnecessarily conservative surgery. For many gliomas, extent of resection matters. Leaving safely removable tumor behind may compromise the oncologic benefit of surgery. That means excellent brain tumor surgery requires navigating between two errors: Going too far. and Not going far enough.

The goal is to find the boundary between them.

So how does a surgeon know when to stop?

This is where modern brain mapping becomes so important. Before surgery, we may combine structural MRI with tools such as:

• functional MRI

• diffusion imaging and tractography

• individualized connectomic analysis

• neuropsychological testing

• detailed neurological examination

These give us a hypothesis about where important networks may be. But during surgery, we can sometimes test those predictions directly.

Using cortical and subcortical stimulation, we can temporarily interrupt tiny regions or pathways and observe what happens. Does speech stop? Does naming become difficult? Does a hand move? Does the patient make a consistent error?

As surgery moves deeper, mapping can help identify how close we are getting to critical white-matter pathways. This is one of the fundamental differences between simply seeing anatomy and understanding functional anatomy. MRI tells us where the tumor is. Mapping helps tell us where the functional boundary is.

Why connectomics changes the conversation

For much of neurosurgical history, the brain was described as a collection of individual regions. Language was “here.” Movement was “there.” Vision was somewhere else. We now understand that the brain works much more like a network. Language depends on multiple regions connected by white-matter pathways. Movement requires communication between cortex, deep nuclei, cerebellum, brainstem, and spinal cord. Attention, decision-making, personality, and memory are even more distributed. That means preserving one small patch of cortex isn't always enough.

We need to think about the connections between regions. This is the idea behind connectome-informed brain tumor surgery: understanding not only where the tumor sits, but which networks pass through and around it.

Why two patients with similar MRIs may have different operations

This is another question families sometimes struggle with. They may find someone online with a tumor that looks remarkably similar and wonder: “Why did that surgeon remove everything, while mine says some tumor should remain?”

The answer is that the MRI is only part of the story. Two tumors that appear similar can differ in:

• molecular biology

• infiltration pattern

• vascular relationships

• hemisphere dominance

• white-matter anatomy

• functional organization

• neuroplasticity

• previous treatments

• patient priorities

The safest boundary may therefore be completely different. There is no universal percentage of tumor that should be removed from every patient. There is an individualized functional boundary.

What should patients ask before brain tumor surgery?

Instead of asking only: “Can you remove the whole thing?”

I think there are better questions:

• What is the realistic goal of my surgery?

• Which brain networks are closest to my tumor?

• What function is most at risk?

• How will you determine the safe boundary during surgery?

• Will you use awake mapping, subcortical stimulation, neurophysiological monitoring, tractography, or other techniques?

• If tumor is intentionally left behind, where will it most likely be and why?

Those questions tell you much more about the surgical strategy than a promised percentage ever could.

The operation is only one part of the treatment

Surgery is enormously important in glioma care. It provides tissue for diagnosis and molecular testing. It can relieve pressure. It can improve symptoms. It can reduce the amount of tumor that subsequent treatments need to control. And, in appropriately selected patients, extent of resection can influence outcomes.

But surgery does not exist in isolation.

Modern brain tumor care may also involve radiation oncology, neuro-oncology, neuropathology, neuroradiology, rehabilitation, genetics, clinical trials, and increasingly molecularly targeted treatments.

The best surgical decision therefore isn't necessarily the operation that produces the cleanest-looking postoperative MRI. It is the operation that puts the patient in the best position for everything that comes next.

The bigger idea: good surgery is not measured only in cubic centimeters

For decades, one of the easiest ways to judge brain tumor surgery was to look at the postoperative MRI.

That's important, but it isn't enough. We should also ask:

• Can the patient speak?

• Can they move?

• Can they see?

• Can they think clearly?

• Can they return home?

• Can they work?

• Can they interact with the people they love?

• And did we accomplish enough oncologically to meaningfully change the trajectory of the disease?

Those outcomes belong in the same equation.

Good brain tumor surgery is aggressive about tumor and conservative about irreplaceable function.

That balance is the real goal of maximal safe resection.

Frequently Asked Questions

Is residual tumor after brain surgery always bad?

Not necessarily. Residual tumor may be intentionally left when removing it would create an unacceptable neurological risk. The significance also depends on tumor type, molecular biology, location, and subsequent treatment options.

Does gross-total resection mean the tumor is cured?

No. Particularly with infiltrating gliomas, microscopic tumor cells can remain beyond what is visible on MRI. Surgery is often one component of a larger treatment strategy.

Why can't surgeons simply see the difference between tumor and normal brain?

Sometimes they can. But infiltrating gliomas often blend into surrounding brain. Technologies such as fluorescence, ultrasound, imaging, mapping, and pathology can help, but none creates a perfect biological boundary.

Is more tumor removal better?

Generally, greater safe extent of resection is desirable in appropriately selected gliomas. The critical qualifier is safe. A major permanent neurological deficit can profoundly change quality of life and the ability to receive additional treatment.

How do surgeons decide when to stop removing a brain tumor?

They integrate anatomy, imaging, tumor characteristics, neurophysiological monitoring, functional mapping, surgical judgment, and the patient's individual priorities. In selected cases, direct brain mapping can identify functional boundaries in real time.

Bottom line

The question in brain tumor surgery isn't simply:

“How much tumor can we remove?”

It is:

“How much tumor can we remove while preserving the networks this person needs to live their life?”

That distinction is the foundation of modern maximal safe resection. As our ability to map individual brain networks improves, the definition of what is safe and what is possible continues to become more personalized.

"Will I really be awake while someone operates on my brain?"

Following the initial shock of a brain tumor diagnosis, this is usually the first question patients ask when I explain that their tumor sits near an important language or movement network and that I recommend waking them up during their surgery to map the brain regions responsible for these functions.

The idea sounds insane. Most people imagine being awake for the entire operation, feeling pain, or somehow watching the surgery unfold.

Fortunately, none of that is true.

Modern awake brain surgery is one of the safest and most carefully choreographed procedures in neurosurgery. Awake brain mapping gives us information that no MRI, CT scan, or computer can currently provide.

Your brain can tell us, in real time, what matters most to you.

Why would anyone stay awake during brain surgery?

Every brain is organized a little differently.

Two people can have tumors in almost exactly the same location, yet one may speak normally after surgery while another could lose the ability to name objects or understand language if the same tissue were removed.

Traditional anatomy gives us an excellent map, but awake mapping gives us your map.

That is especially important when tumors are located near networks controlling:

• language

• movement

• vision

• attention

• executive function

• reading

• social cognition

The purpose of keeping you awake is to remove as much tumor as possible without removing the person you are.

A day in the operating room

It’s honestly a pretty normal day…

Before surgery

You meet your surgical team.

The anesthesiologist explains how you'll be kept comfortable.

Your neuropsychologist or speech therapist reviews the language tasks you'll perform.

Nothing is a surprise.

By the time you enter the operating room, you've already practiced everything.

Going to sleep

You initially go to sleep.

I’ll repeat that: YOU GO TO SLEEP!!!!

Patients are not rolled into the operating room awake while surgeons begin operating. After you receive some anesthesia, your head is comfortably secured so it cannot move during surgery. Your scalp is completely numbed with local anesthetic. The brain itself has no pain receptors. This is usually one of the most surprising facts for most families.

Waking up

After the skull has been opened and everything is ready, anesthesia is gradually lightened. Most patients wake up surprisingly calmly. Many tell me it feels more like waking from a nap than waking in the middle of surgery.

They aren't watching surgery. They don't see the operation. Instead, they hear familiar voices asking simple questions. Often they may feel cold from irrigation on their scalp, or they may want to reposition themselves a bit to get more comfortable.

What do patients actually do?

This is where the magic happens.

You may be asked to:

• name pictures

• count numbers

• read sentences

• repeat words

• move your hand

• move your foot

• answer simple questions

• identify emotions

• describe objects

The exact tasks depend entirely on where the tumor sits. A tumor near language networks requires different testing than one near movement or vision. The tasks themselves are typically performed before the operation so there is nothing unexpected during the procedure. While the patient participates in the tasks being tested, the surgeon begins mapping their brain.

What is brain mapping?

Small electrical pulses are briefly delivered to the brain's surface. These pulses do not damage the brain. Instead, they create a temporary, reversible interruption of normal activity. The analogy i use is to imagine briefly muting one musician in an orchestra. The music changes for only a few seconds. Then everything returns immediately.

If stimulation temporarily prevents a patient from naming a picture, we've identified tissue that's participating in language. If stimulation causes weakness, we've found movement pathways. Those areas become boundaries we label and work around to preserve the associated function.

Why mistakes are actually good

I know this sounds backwards. During surgery, we actually hope to see small, temporary mistakes. If a patient suddenly cannot name "camel" or "umbrella" while we're stimulating one tiny location, we've learned something incredibly valuable. That tiny mistake prevents a permanent one. Those brief errors help us preserve speech, reading, movement, and independence.

Can you feel the surgery?

Almost everyone asks this.

The answer is no. The scalp is numb. The brain itself cannot feel pain.

Some patients notice:

• vibration

• pressure

• irrigation fluid

• conversation in the room

But pain during mapping is uncommon. Depending on the location of the procedure, the muscle that helps you chew can cause discomfort. Your anesthesia team continuously adjusts medications to keep you comfortable.

What if I can't do the tasks?

Patients often worry they'll fail. There isn't a test to pass. We're learning how your brain works. If you're tired, anxious, or make mistakes naturally, that's part of the information. The goal is understanding which regions are important for you.

Is awake surgery right for everyone?

No.

Many brain tumors can be removed safely while patients remain asleep. Awake surgery is most valuable when tumors sit close to important functional networks where real-time testing can meaningfully improve safety. Whether someone is a good candidate depends on the tumor, the planned operation, and the patient. Most brain tumor surgery don’t require awake mapping.

What surprises patients most afterward?

When I ask patients after surgery what surprised them most, I often hear the same answers:

"It wasn't nearly as scary as I imagined."

"I don't remember as much as I thought I would."

"The team was talking to me the whole time."

"It felt incredibly organized."

That's exactly the goal.

Awake brain surgery should never feel chaotic. It should feel carefully rehearsed, calm, and focused on protecting what makes you, you.

The bigger picture

One of the most common misconceptions about brain surgery is that it's about removing as much tumor as possible.

Sure. We want that…

…but modern neurosurgery is more nuanced than that. The goal is removing as much tumor as we can safely while preserving the networks that allow you to speak with your children, recognize your spouse, read a book, play the piano, return to work, or tell your own story.

Sometimes the safest operation is also the smartest one. Awake brain mapping helps us find that balance.

Frequently Asked Questions

Will I be awake the entire surgery?

Usually no. Most awake brain surgeries use an "asleep-awake-asleep" or similar technique, where you're asleep for the beginning and end of the operation and awake only during the mapping portion.

Can I panic during surgery?

The operating room team is highly experienced in helping patients stay calm and comfortable. Careful preparation before surgery is one of the biggest reasons these procedures go so smoothly.

What happens if I can't talk during the operation?

That's actually valuable information. Temporary changes during stimulation help identify brain regions that should be protected.

Is awake surgery safer?

For carefully selected tumors near critical functional areas, awake mapping has been associated with greater preservation of neurological function while still allowing extensive tumor removal.

Final Thoughts

One of the greatest advances in modern brain tumor surgery is the realization that every brain has its own unique functional map.

Awake brain surgery allows us to discover that map in real time. Rather than relying only on what we expect to find, we can listen to the brain itself and let it guide the safest path forward.

About this series. We’ve walked through the brain by location—frontal, temporal, parietal, insula/operculum, occipital, medial networks, deep pathways, callosum, cerebellum, brainstem—and built a “highway map” of white matter. Now we pivot to the question patients ask next: what changes when the tumor is slow-growing?

Why low-grade gliomas are different

Low-grade gliomas (LGG) often unfold over years, not weeks. That changes everything:

• The brain has time to adapt (plasticity).

• Symptoms are often subtle: seizures, word-finding fatigue, slower processing, personality drift.

• Treatment becomes a strategy more than a single event.

Takeaway: High-grade disease is often about urgency and maximal safe cytoreduction. Low-grade disease is about timing, networks, and preserving a life over decades.

Plasticity in plain English

Plasticity is the brain’s ability to reroute function when it has time:

• Nearby regions can “pick up the slack.”

• Networks can shift their balance.

• Patients can look normal in clinic yet still feel subtle changes at work or home.

But plasticity has limits:

• Some pathways are more “moveable” than others.

• Rewiring is easier for skills than for critical cables (like the internal capsule or optic radiations).

• Plasticity is not a guarantee. It is more like a window of opportunity.

Why location matters even more in LGG

In low-grade tumors, the goal is not only removing tumor safely. The goal is to protect function for the next 10–30 years while planning for likely future steps.

Here’s the quick location-based logic:

Frontal lobe (common)

• Typical LGG story: seizures, subtle executive/behavioral shifts, fatigue with complex tasks.

• Network risk: initiation and control systems; language if dominant side.

• Strategy shift: We rely more on staged decisions. Maximize safe resection while protecting long-range control networks; plan for rehab and cognitive pacing.

Temporal lobe

• Typical story: seizures; naming, memory, or word-meaning fatigue.

• Network risk: ventral language and hippocampal memory circuits.

• Strategy shift: task selection matters (meaning vs repetition vs names), and memory lateralization informs risk/benefit.

Insula/operculum

• Typical story: seizures, subtle speech effort issues, visceral/taste auras.

• Network risk: articulation + salience + nearby semantic tracts; vessel adjacency.

• Strategy shift: corridor-first planning + mapping of articulation/semantics; avoid “small vascular tax” that accumulates over years.

Parietal lobe

• Typical story: “off” attention/space, clumsy multistep actions, subtle reading difficulty.

• Network risk: attention networks (DAN/VAN), praxis, optic radiations (upper fibers).

• Strategy shift: awake tasks that reveal neglect/praxis deficits early; protect independence functions.

Occipital lobe

• Typical story: visual field changes that patients notice constantly.

• Network risk: optic radiations and V1 map.

• Strategy shift: be conservative near vision cables; even small field cuts carry high daily cost.

Medial frontal / SMA

• Typical story: initiation and bimanual issues; transient SMA syndrome is common.

• Network risk: start signal and sequencing pathways.

• Strategy shift: counsel about short-term dip; focus on recovery pathway, not just resection.

Deep pathways (basal ganglia/thalamus/internal capsule)

• Typical story: small changes feel big.

• Network risk: dense motor/sensory highways.

• Strategy shift: diagnosis and stability often trump aggressive removal; corridor-first and “stop rules” matter.

How the surgical strategy changes in low-grade glioma

1) Timing becomes part of treatment

In LGG, decisions often revolve around:

• symptoms (especially seizures)

• growth pattern over time

• molecular features and patient goals

• network proximity and “functional budget”

Many patients benefit from earlier maximal safe resection, but the key is individualized: remove tumor when it’s safest for networks, not when it’s most emotionally urgent.

2) Awake mapping becomes more valuable (not less)

Because the goal is long-term function, teams use:

• language tasks that test both sound and meaning routes

• executive tasks (planning/switching) for frontal/parietal adjacency

• reading and naming precision tasks for temporal/occipito-temporal regions

• bimanual and initiation tasks for medial frontal

3) “Supratotal” thinking is different in LGG

In some LGG cases, teams may resect beyond the obvious MRI abnormality only when the network map and testing allow it. The decision isn’t “be aggressive.” It’s “be aggressive where the brain can afford it.”

4) Staged surgery is not a failure

LGGs may be managed with:

• an initial debulking that is network-safe

• time for plasticity and rehabilitation

• a second-stage resection later as networks reorganize
  This can preserve function while still improving tumor control.

What patients can do with this information

If you have a low-grade glioma, these are smart questions:

• Which tracts are closest to my tumor?

• Which functions are at risk: language, memory, attention, vision, initiation?

• How will you test those functions (awake mapping, tasks, monitoring?)

• Is earlier resection safer than waiting, or does waiting improve mapping options?

• What’s the long-term plan if this changes over years?

Bottom line

Low-grade glioma care is the long game. The brain often has time to adapt. This ability is not infinite though. The best outcomes come from aligning location, networks, timing, and patient goals into a plan that preserves function now and keeps options open later.

Fast FAQ

Does slow-growing mean “benign”?
No. “Low-grade” describes growth behavior, not harmlessness. LGGs can still disrupt networks and may progress over time.

If I feel fine, do I still need treatment?
Sometimes yes. This is especially true if the tumor is growing or living near critical tracts. “Feeling fine” can coexist with subtle cognitive changes that mapping can detect.

Can the brain really rewire language or movement?
Often, to a degree. It is especially true with slow growth and good rehab. But some highways are less flexible, and that’s why individualized mapping matters.

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the brainstem is different

The brainstem is the narrow stalk connecting brain to spinal cord. It’s small, dense, and essential. In a few centimeters it contains:

• the main motor and sensory highways for the whole body

• the control centers for eye movements, facial function, swallowing, and voice

• circuits involved in breathing, heart rate, and alertness

That’s why in the brainstem, millimeters matter. Even benign-appearing lesions can cause major symptoms, and treatment decisions are often less about “removing everything” and more about protecting function.

Takeaway: Brainstem tumors are about pathways and safety strategy first—then tumor control.

The brainstem map

Think of three stacked levels:

1) Midbrain (top)

• Main jobs: eye movement control, pupil function, arousal circuits

• Common cranial nerves here: III (oculomotor), IV (trochlear)

• If affected: double vision, eyelid droop, pupil changes, imbalance

2) Pons (middle)

• Main jobs: face sensation/movement, hearing/balance integration, coordination links

• Cranial nerves here: V (trigeminal), VI (abducens), VII (facial), VIII (vestibulocochlear)

• If affected: facial numbness/weakness, eye movement problems, vertigo, hearing symptoms, ataxia

3) Medulla (bottom)

• Main jobs: swallowing, voice, breathing and heart regulation

• Cranial nerves here: IX (glossopharyngeal), X (vagus), XI (accessory), XII (hypoglossal)

• If affected: dysphagia, hoarseness, weak cough, tongue weakness, breathing issues

The “long tracts” (the major highways passing through)

These are the most important “wires” to picture:

Corticospinal tract — strength and motor control

• What it does: carries “move” signals from brain to spinal cord

• If affected: weakness, clumsiness, spasticity, slowed fine motor

Medial lemniscus — fine touch and position sense

• What it does: vibration/position sense (proprioception)

• If affected: numbness, poor balance in the dark, clumsy hand placement

Spinothalamic tract — pain and temperature

• What it does: pain/temp pathways

• If affected: altered pain/temp sensation on the opposite side of the body

Reticular activating system — alertness

• What it does: keeps you awake and cognitively “online”

• If affected: unusual sleepiness, slowed processing, fluctuating attention

Common signs you might notice

Brainstem symptoms often come in combinations because everything is tightly packed:

• Double vision or trouble moving one eye (especially looking sideways)

• Facial numbness or tingling, sometimes with jaw pain

• Facial weakness (droop, eye closure trouble)

• Unsteady gait / ataxia (especially with pons/cerebellar connections)

• Swallowing trouble, coughing with liquids, hoarse voice

• Weakness on one side or both

• Odd sensory changes (pain/temp vs vibration/position feel different)

• Sleepiness or mental “fog” that seems out of proportion

Red flags: progressive swallowing difficulty, weak cough, breathing changes, or rapid neurologic decline deserve urgent evaluation.

How teams plan care (Before • During • After)

Before treatment

• Clarify the goal: In adults, many brainstem lesions are treated with a strategy of diagnosis + targeted therapy, rather than aggressive resection.

• Imaging detail matters: high-quality MRI (with diffusion and contrast patterns) to estimate whether lesion is focal/exophytic vs infiltrative.

• Decide on tissue diagnosis: biopsy can be essential when imaging is uncertain or when molecular information will change therapy.

• Baseline exam: eye movements, facial sensation/motor, swallowing/voice, strength, coordination, and a clear symptom diary.

During procedures (when biopsy or surgery is done)

• Route selection is everything: surgeons choose corridors that minimize crossing long tracts and protect perforating vessels.

• Neuromonitoring: motor/sensory evoked potentials and cranial nerve monitoring when relevant.

• A strict stopping rule: if mapping/monitoring signals risk to key pathways, the safest move is to stop.

After treatment

• Swallow and airway first (medulla/lower pons): early speech-language evaluation, diet modification, cough-strength strategies.

• Eye/vision rehab: prisms, patching strategies, vestibular therapy when dizziness is prominent.

• PT/OT: gait stability, fall prevention, and fine motor retraining.

• Fatigue/alertness plan: sleep optimization, pacing, and cognitive rehab when needed.

Ask your surgeon (patient-facing)

• Which brainstem level is involved—midbrain, pons, or medulla—and what does that predict?

• Do you recommend biopsy to guide therapy, and what route would you use?

• What neuromonitoring will be used to protect motor/sensory tracts and cranial nerves?

• What symptoms should trigger urgent reassessment (swallowing, breathing, vision)?

Bottom line

Brainstem tumors sit beside the nervous system’s most essential pathways. Good care is strategy-driven: define the goal, get the right diagnosis, choose corridors carefully, and protect long tracts and cranial nerves. Recovery often depends as much on early rehab—swallowing, eye control, gait—as it does on the tumor itself.

Fast FAQ

Are brainstem tumors always inoperable?
No. Some are focal or grow outward (exophytic) and may be partially resectable. Many adult brainstem tumors, however, are best managed with biopsy plus medical therapy.

Why is biopsy sometimes recommended even when MRI “suggests” a diagnosis?
Because treatment increasingly depends on molecular features, and imaging alone can be misleading.

Can symptoms improve?
Often yes—especially if symptoms are driven by swelling or compression. Rehab is critical for swallowing, gait, and eye control.

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the cerebellum matters

The cerebellum sits in the back of the head, below the cerebral hemispheres. Most people associate it with balance. But it’s better described as the brain’s timing and calibration engine—for movement, eye control, speech rhythm, and even the “smoothness” of thinking.

The posterior fossa is also a tight space. Small changes from swelling or CSF blockage can cause symptoms quickly. So planning is about networks and pressure/CSF pathways.

Takeaway: Cerebellar tumors can affect walking, eye movements, coordination, and speech cadence. Location inside the cerebellum predicts which of those are most at risk.

Cerebellar anatomy in one minute (the map that matters)

Think of the cerebellum in three layers:

1) Vermis (midline)

• Function: trunk posture, gait stability, “staying upright.”

• Symptoms if affected: wide-based walking, veering, falls on turns.

2) Cerebellar hemispheres

• Function: fine control of limbs—precision reaching, smooth hand movements.

• Symptoms if affected: overshooting targets (dysmetria), tremor-like wobble, clumsy hands.

3) Flocculonodular lobe (inferior/posterior, near brainstem)

• Function: balance integration and eye stabilization (vestibular system).

• Symptoms if affected: vertigo-like dizziness, nystagmus (eye jitter), nausea, “bouncing” vision.

And the key output “highways” that carry cerebellar signals:

• Dentate nucleus (deep cerebellar “output station” for coordination and cognitive pacing)

• Superior cerebellar peduncle (SCP) → crosses to the other side → red nucleus/thalamus → motor and prefrontal cortex

• Middle cerebellar peduncle (MCP) brings in cortical information via the pons (planning inputs)

• Inferior cerebellar peduncle (ICP) brings vestibular and sensory inputs (balance and body-state)

Cerebellar networks in plain English (with anatomy)

1) Cerebello–thalamo–cortical loop — timing & smoothness circuit

• Anatomy: dentate nucleus → SCP → (crosses) → thalamus → motor/premotor and prefrontal cortex.

• What it does: smoothness of movement, motor learning, pacing; also contributes to “mental tempo.”

• If affected: clumsiness, slowed coordination; sometimes “my thinking feels delayed,” especially when dentate/SCP are involved.

2) Vestibulo-ocular network — balance + gaze stability

• Anatomy: flocculonodular lobe + vestibular nuclei ↔ ICP pathways; integrates with eye movement centers.

• What it does: keeps vision stable when your head moves (VOR) and keeps the world from “bouncing.”

• If affected: dizziness, nausea, nystagmus, double vision, motion intolerance.

3) Spinocerebellar / proprioceptive calibration — where your body is in space

• Anatomy: sensory/proprioceptive inputs via ICP, plus midline vermis processing.

• What it does: calibrates posture and gait in real time.

• If affected: unsteady stance, “drunk walk” feeling, worsens in low light.

4) Cerebellar speech timing — rhythm and cadence

• Anatomy: hemispheric cerebellum + dentate outputs to speech-motor planning cortex.

• What it does: makes speech smooth and rhythmic.

• If affected: scanning speech (choppy cadence), slurring, fatigue-related speech breakdown.

Common signs you might notice

• Gait issues (vermis): wide stance, veering, trouble turning, falls.

• Limb coordination (hemisphere): overshooting when reaching, shaky handwriting, dropping objects.

• Eye/balance (flocculonodular/ICP): dizziness, nausea, bouncing vision, double vision.

• Speech (dentate/SCP): choppy rhythm, slurred articulation.

• Pressure red flags: headache + vomiting + increasing sleepiness can signal CSF blockage.

The neighbors that shape urgency

• Brainstem: vital pathways + cranial nerve nuclei (swallowing, facial movement, eye control).

• Fourth ventricle / aqueduct: CSF flow channels—blockage can cause hydrocephalus.

• Cranial nerves and vascular structures: delicate in the posterior fossa; traction matters.

How teams plan surgery (Before • During • After)

Before surgery

• Define location precisely: vermis vs hemisphere vs flocculonodular region; relationship to dentate and SCP.

• Hydrocephalus plan: evaluate fourth ventricle compression and decide if CSF diversion is needed.

• Baseline exam: gait, finger-to-nose, heel-to-shin, eye movements (nystagmus), swallowing screen if needed.

During surgery

• Corridor selection: midline vs hemispheric approach based on which cerebellar “zone” is involved.

• Monitoring: brainstem/cranial nerve monitoring when close; careful handling of cerebellar tissue to avoid traction injury.

• Protect outputs: be deliberate around the dentate nucleus and SCP when they’re near the tumor—these are high-yield pathways for long-term coordination.

After surgery

• Early mobilization: gait and balance improve with practice—PT begins early.

• Vestibular rehab: gaze stabilization exercises, graded motion exposure, nausea control.

• Speech therapy: for scanning speech or slurring.

• Watch pressure: worsening headache/vomiting/somnolence warrants urgent reassessment.

Ask your surgeon (patient-facing)

• Is the tumor closer to the vermis, a hemisphere, or the flocculonodular region?

• Are the dentate nucleus or superior cerebellar peduncle nearby?

• What’s my risk of hydrocephalus, and how will you monitor/treat it?

• What rehab starts right away (balance, vestibular, speech)?

Bottom line

Cerebellar tumors affect networks for coordination, balance, gaze stability, and speech timing. Anatomy predicts function: vermis = gait, hemisphere = limbs, flocculonodular = dizziness/eyes, dentate/SCP = output and pacing. With careful corridors, pressure management, and early rehab, many patients recover stability and independence.

Fast FAQ

Is dizziness from a cerebellar tumor the same as an inner ear problem?

It can feel similar, but here the problem is the brain’s integration of balance and eye signals—not the ear alone.

Can balance improve after surgery?

Often yes—especially when swelling resolves and vestibular/gait therapy starts early.

Why are headaches and vomiting such a big deal in posterior fossa tumors?

They can signal rising pressure from blocked CSF flow. That pattern deserves urgent evaluation.

Post 10: A Field Guide to White Matter (Patient Edition)

About this series. These posts explain where adult gliomas begin and which brain networks are at risk—plain English for patients, families, and referring clinicians.

First: what is “white matter”?

If gray matter is the brain’s “neighborhoods” (where processing happens), white matter is the wiring. White matter is the long cables that connect neighborhoods into working networks.

Gliomas often don’t just grow as a lump. They can travel along these cables. That’s why modern planning talks so much about tracts, networks, and “maximal safe” resection.

Takeaway: Symptoms and surgical risk often depend on which highway a tumor touches, not just which lobe it’s in.

The 10 highways you’ll hear about most

1) Arcuate / SLF (dorsal language route)

Connects: back/side (temporo-parietal) ↔ front (inferior frontal). Does: speech sound-to-motor timing, repetition, phonology. If disrupted: scrambled words, repetition trouble, “word is there but comes out wrong.”

2) IFOF / Extreme Capsule (ventral language route)

Connects: frontal ↔ temporal/occipital via deep “meaning” pathway. Does: word meaning, semantics, comprehension nuance. If disrupted: fluent but vague speech, low-frequency words slip, comprehension feels thin.

3) Uncinate Fasciculus

Connects: anterior temporal pole ↔ orbitofrontal/frontal. Does: names, emotion-language links, memory-to-meaning. If disrupted: trouble with proper names, subtle personality/emotional tone shifts.

4) Frontal Aslant Tract (FAT)

Connects: SMA/pre-SMA ↔ inferior frontal speech planning regions. Does: speech start, volitional initiation, verbal fluency. If disrupted: long pauses before speaking, “can’t get started,” effortful speech onset.

5) Cingulum Bundle

Connects: medial frontal ↔ parietal ↔ medial temporal (a midline “belt”). Does: motivation/drive, attention stability, error-checking context. If disrupted: apathy-like low drive, mental fatigue, drifting attention.

6) Corpus Callosum (the bridge)

Connects: left ↔ right hemisphere (genu/body/splenium). Does: integration, bimanual coordination, attention sharing. If disrupted: slowed processing, split-attention issues, bimanual clumsiness; “butterfly” spread pattern.

7) Optic Radiations (vision cables)

Connects: thalamus (LGN) ↔ occipital visual cortex (V1). Does: visual fields (upper/lower quadrants). If disrupted: “pie in the sky” (upper field loss, Meyer’s loop) or “pie on the floor” (lower field loss).

8) Internal Capsule (superhighway)

Connects: cortex ↔ brainstem/spinal cord; sensory ↔ cortex. Does: motor strength pathways, sensation pathways (densest wiring in brain). If disrupted: weakness, numbness, clumsy proprioception—small injuries can be big.

9) Inferior Longitudinal Fasciculus (ILF)

Connects: occipital (visual) ↔ temporal (object/meaning). Does: visual recognition, reading fluency, faces/objects. If disrupted: trouble recognizing faces/objects; reading becomes effortful.

10) Cerebello–thalamo–cortical loop (coordination circuit)

Connects: cerebellum ↔ thalamus ↔ cortex. Does: coordination, timing, smoothness, some cognitive pacing. If disrupted: imbalance, clumsiness, slowed cognitive tempo (depending on nodes involved).

A quick symptom translator (common phrases → likely highway)

• “Words are scrambled / repetition is hard” → Arcuate/SLF

• “Fluent but vague / names disappear” → IFOF/Uncinate

• “Can’t get started speaking” → FAT / SMA loop

• “Low drive, not sad—just flat” → Cingulum / medial networks

• “A corner of vision is missing” → Optic radiations

• “Weakness or numbness came suddenly” → Internal capsule proximity

• “Two hands don’t cooperate” → Corpus callosum / SMA

• “Faces/objects feel unfamiliar” → ILF / ventral visual stream

How this changes surgery (in plain English)

Modern tumor surgery is network surgery. We try to:

1. See the highways ahead of time (tractography/connectome planning).

2. Test what matters during surgery (awake mapping when appropriate).

3. Know the stop points near critical tracts (subcortical mapping and monitoring).

4. Plan recovery around the specific networks at risk (targeted rehab).

Ask your surgeon

• Which tracts/highways are closest to my tumor?

• Will you use awake mapping or monitoring to protect them—and what tasks?

• If you have to choose, what function is the highest priority to preserve for my life and work?

Fast FAQ

Are tracts the same in every person? The big highways are consistent, but the exact course varies. Tumors can also shift or reorganize function—one reason individualized mapping helps.

Does tractography guarantee safety? No. It’s a map, not reality. The best approach combines imaging with intraoperative testing and a clear stopping rule.

Why do some deficits improve over weeks? Swelling and temporary network disruption often recover. Rehab helps the brain reroute and compensate.

Post 9: Corpus Callosum (“Butterfly” Gliomas)

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the corpus callosum matters

The corpus callosum is the brain’s main bridge between the left and right hemispheres. It’s a dense white-matter highway. Tumors that reach it can spread along the bridge, sometimes creating the classic “butterfly” appearance which is really just one tumor mass that extends into both sides.

Takeaway: A callosal tumor is less about a single “lump” and more about a tumor tracking along the brains connections. Treatment decisions focus on function, safety, and realistic goals.

The corpus callosum in plain English

The callosum is organized front to back:

• Genu (front): connects frontal lobes → planning, initiation, attention control

• Body (middle): connects motor and sensory regions → coordination, both-hand tasks

• Splenium (back): connects parietal/occipital regions → visuospatial integration and visual processing

When a glioma involves the callosum, symptoms depend on which segment and which nearby networks are affected.

What dysfunction can look like (real-world examples)

Callosal involvement doesn’t usually produce one dramatic, obvious deficit. It often shows up as changes in integration:

• Slowed processing: “Everything takes longer,” mental fatigue spikes quickly.

• Split attention issues: harder to multitask; can’t hold two streams of info at once.

• Bimanual clumsiness: buttons, tying shoes, cooking with both hands feels off.

• Initiation/drive changes: when cingulate/medial frontal networks are involved, this can come across as reduced spontaneity, apathy-like symptoms.

• Visuospatial integration issues: especially with posterior callosum involvement - Navigation feels harder, reading/visual scanning gets less fluid.

In some cases, disconnection phenomena can occur (rare, usually more extensive): one hand “doesn’t cooperate,” or actions feel oddly uncoordinated.

Why “butterfly” happens

Glioma cells preferentially migrate along white-matter tracts. The callosum is the biggest tract bundle in the brain. So when a tumor reaches it, it has a ready-made route to the other hemisphere, creating a symmetric, midline-crossing pattern on MRI.

The nearby “do-not-disturb” structures

Callosal tumors sit close to critical midline anatomy:

• Pericallosal/callosomarginal arteries (blood supply along the callosal surface)

• Cingulum bundle (motivation, attention, error-monitoring—runs just above/around)

• Deep ventricular/periventricular pathways (dense fibers near the lateral ventricles)

• SMA/medial frontal networks (especially with anterior involvement)

This is why corridor selection is everything.

How teams plan care (Before • During • After)

Before surgery

• Define the goal: biopsy for diagnosis? Debulking to relieve mass effect? Maximal safe resection? Minimally invasive Laser Ablation (my favorite…) The answer depends on symptoms, tumor biology, and location within the callosum.

• Map networks: relationship to cingulum, SMA, deep periventricular fibers, and frontal/occipital connections.

• Baseline function: attention/processing speed, bimanual tasks, initiation and mood/energy profile, plus standard motor/sensory/visual fields.

During surgery

• Corridor-first mindset: anterior vs posterior approach depending on genu/body/splenium involvement; avoid vascular injury along the callosal surface.

• Monitoring and mapping: motor/sensory monitoring as relevant; subcortical mapping when approaching deep fibers.

• A realistic stopping rule: when you’re near pathways where “one more millimeter” risks a disproportionate loss of independence, the safest operation is the one that stops.

After surgery

• Rehab focuses on integration: pacing strategies, dual-task training, bimanual coordination drills, and attention scaffolding.

• Expect fatigue: cognitive fatigue is common. Recovery plans often emphasize structured routines and graded activity.

• Support initiation: if drive is reduced, external prompts and scheduled activation help while networks recalibrate.

Ask your surgeon (patient-facing)

• Is the tumor in the genu, body, or splenium, and what functions does that threaten?

• What is the plan: biopsy, debulking, or maximal safe resection—and why?

• How close are we to the cingulum and SMA/medial networks?

• What do you expect to be temporary swelling-related changes vs longer-term risks?

• What rehab is planned for attention, fatigue, and bimanual coordination?

Bottom line

Corpus callosum (“butterfly”) gliomas are tumors of connections. The callosum is the brain’s main bridge, so involvement often affects processing speed, attention integration, and bimanual coordination. The best care is goal-driven and corridor-first—protecting midline vessels and nearby medial networks while selecting treatments that preserve independence.

Fast FAQ

Does a “butterfly” pattern mean surgery isn’t possible? Not automatically. It means decisions must be individualized. Sometimes biopsy plus medical therapy is best; sometimes, biopsy plus LITT plus medicine is best, and sometimes debulking helps symptoms. The key is a realistic goal and a safety-first plan.

Why do people feel “foggy” or slow with callosal tumors? Because the hemispheres share work through the callosum. When the bridge is disrupted, integration becomes inefficient.

Can rehab help? Yes—especially with cognitive pacing, attention strategies, and bimanual retraining. Even when MRI changes are limited, training can improve day-to-day function.

Post 8: Basal Ganglia & Thalamus (Deep Pathways)

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why “deep” tumors are different

The basal ganglia and thalamus sit deep in the center of the brain—surrounded by critical “wiring” that carries movement, sensation, vision, and attention. In this region, millimeters matter: a small injury can create a big change in function, not because the surgery is sloppy, but because the pathways are densely packed.

Takeaway: Deep glioma surgery is less about “getting to the tumor” and more about choosing the safest corridor around the internal capsule and thalamic highways.

The deep structures in plain English

1) Basal ganglia — the brain’s movement “gatekeeper”

Think of the basal ganglia (caudate, putamen, globus pallidus) as a system that:

• Starts movements smoothly

• Stops unwanted movements

• Helps automate habits and motor routines

If affected: slowed movement (bradykinesia), stiffness, reduced facial expression, trouble with smooth walking, or occasional involuntary movements depending on circuits involved.

2) Thalamus — the brain’s relay hub

The thalamus is like Grand Central Station for signals going to the cortex:

• Sensation (touch, pain, temperature, proprioception)

• Motor planning loops (cortex ↔ thalamus ↔ cortex)

• Attention and arousal

• Parts of vision and language networks through thalamo-cortical connections

If affected: numbness/tingling, altered sensation, fatigue/sleepiness, attention fog, or in some cases thalamic pain syndrome (later).

The real “do not disturb” neighbors (white-matter highways)

Internal capsule — the main cable bundle

This is the densest concentration of “wires” in the brain:

• Motor fibers (cortex → spinal cord)

• Sensory fibers (body → cortex)

• Visual and associative fibers depending on level

Why it matters: Tiny shifts can cause weakness or sensory loss.

Optic tract / optic radiations adjacency

Depending on location, deep lesions can threaten vision pathways.

Thalamo-cortical radiations

Fibers that carry sensory and attention signals to cortex.

Arcuate/IFOF neighborhood (dominant hemisphere)

Deep lesions extending laterally can approach language tracts.

What dysfunction can look like (real-world examples)

• Weakness: one arm feels heavy; foot drags; fine motor slows.

• Numbness: “cotton glove” sensation; reduced position sense (clumsy without looking).

• Coordination vs strength confusion: strength may test “okay,” but motion is slow, awkward, or poorly initiated.

• Attention/arousal: unusually sleepy, foggy, slower processing.

• Vision: bumping into things on one side; missing a portion of the visual field.

• Speech/fluency (some cases): slowed output or reduced spontaneity if loops are affected.

How teams plan surgery (Before • During • After)

Before surgery

• Define the goal: biopsy vs maximal safe resection vs staged therapy—based on tumor biology, symptoms, and risk.

• Map the corridors: advanced imaging to visualize relationship to the internal capsule, thalamic nuclei, and nearby vision/language pathways.

• Plan the route: pick a surgical path that avoids crossing dense fiber bundles—sometimes a longer route is safer.

• Baseline testing: strength, coordination, sensation, visual fields, and a quick attention/processing screen.

During surgery

• “Corridor-first” mindset: the approach is the operation.

• Neuromonitoring: continuous motor evoked potentials and somatosensory evoked potentials when relevant.

• Subcortical mapping: identify “stop points” near the internal capsule—when stimulation triggers motor response at low thresholds, you’re near critical fibers.

• Gentle technique: minimal retraction, careful hemostasis, protect perforators.

After surgery

• Early neuro checks: strength, sensation, vision, alertness—frequent and standardized.

• Rehab tailored to pathway: OT/PT for capsule-related weakness, sensory retraining for thalamic symptoms, cognitive pacing for attention/arousal changes.

• Manage swelling: deep regions can be sensitive to edema; expectations and steroid taper matter.

Ask your surgeon (patient-facing)

• How close is this tumor to the internal capsule?

• What is the plan: biopsy, Laser Ablation (LITT), partial resection, maximal safe resection, or staged therapy?

• What monitoring will you use (MEPs/SSEPs, subcortical mapping)?

• What deficits are temporary from swelling vs more likely to persist?

• If vision or language pathways are nearby, how are they being mapped?

Bottom line

Basal ganglia and thalamic gliomas sit beside the brain’s densest highways. The safest strategy is built around corridor selection, real-time monitoring, and knowing when to stop to protect the internal capsule and thalamo-cortical pathways—because in the deep brain, a few millimeters is the difference between independence and disability.

Fast FAQ

Do deep tumors always need surgery? Not always. Sometimes biopsy plus chemo/radiation is safest. Sometimes minimally invasive ablation is possible with tools likes Laser Ablation (LITT procedure). Surgery is considered when symptoms, size, growth pattern, or molecular profile justify the risk.

Why can weakness appear even if surgery “went well”? Swelling near the internal capsule can temporarily affect fibers. Many deficits improve as edema resolves and rehab kicks in.

Is the thalamus only sensation? No. It also influences attention, alertness, motor loops, and cognitive processing—so symptoms can feel “global.”

Post 7: Cingulate & Medial Networks

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the cingulate & medial networks matter

Running along the brain’s midline, the cingulate gyrus is a control center for motivation, focus, error-checking, and emotion-attention balance. Tumors here don’t usually knock out strength or speech outright—but small missteps can blunt drive, flatten initiative, and disrupt how we shift focus or evaluate mistakes.

Takeaway: Medial tumors live where motivation (“I want to start”), monitoring (“I’m on track”), and mood/attention coupling meet. Good planning protects these day-to-day abilities while pushing safe resection.

Medial networks in plain English

1) Anterior cingulate (ACC) — drive, focus, and switching

• What it does: Helps start and sustain effort, decide what deserves attention, and switch when needed.

• If affected: Feels like apathy or reduced get-up-and-go; harder to shift gears; tasks stall without prompting.

2) Dorsal ACC–prefrontal loop — error monitoring & conflict control

• What it does: Notices mistakes fast and helps you course-correct.

• If affected: More slips on routine tasks; people say “I know what to do, but I keep drifting.”

3) Default Mode Network (DMN, medial fronto-parietal) — inner narration & context

• What it does: Background self-talk and context building; toggles with attention networks.

• If affected: Mind-wandering at the wrong time; trouble holding the “big picture” while doing details.

4) Salience coupling (anterior insula ↔ ACC) — what matters now

• What it does: Flags important cues and flips you from “resting” to “task mode.”

• If affected: Blunted urgency; delayed pivot from planning to doing.

5) Cingulum bundle (white-matter “belt”) — the wiring

• Where it runs: Arches under the cingulate, connecting medial frontal ↔ parietal ↔ temporal/limbic hubs.

• If affected: Subtle memory/attention drift, fatigue, slower mental set-shifting.

Common signs you might notice

• Low drive or slowed initiation despite intact strength and language.

• Harder to switch between tasks; lingering on one step.

• More small mistakes unless someone cues you.

• Mood/attention coupling feels off: either dulled urgency or emotional over-reactions to small errors.

• Fatigue out of proportion to effort, with normal basic labs.

The nearby “roads” (white-matter to protect)

• Cingulum bundle (medial fronto-parietal/limbic connector).

• Callosal fibers (interhemispheric links for bimanual/medial control).

• Frontal aslant tract (FAT) anteriorly (volitional speech/initiating sequences).

• Superior longitudinal fascicles edges laterally (attention switching).

How teams plan surgery (Before • During • After)

Before surgery

• Imaging & tractography: Map tumor relation to cingulum, callosum, and FAT; confirm distance from SMA and primary motor.

• Baseline measures: simple initiation tasks, set-shifting (alternating numbers/letters), error-monitoring drills (Stroop-style), mood/energy scales.

• Expectation-setting: emphasize that changes in drive/focus can occur transiently and often improve with structured rehab.

During surgery

• Strategy: Midline-sparing corridors; respect pericallosal/callosomarginal arteries and bridging veins.

• Mapping (awake or asleep with monitoring):

  • Initiation/sequencing: paced finger/word starts; dual-task switching.

  • Error monitoring: quick conflict tasks (e.g., color-word, handedness judgment).

  • Subcortical stimulation: guard the cingulum and midline callosal fibers when working deep/medial.

After surgery

• Rehab focused on control systems: external pacing, checklisting, task chunking, and interval breaks; consider cognitive rehab.

• Energy & mood supports: sleep hygiene; therapy when mood-attention coupling is off; gradual load-building.

• Follow-up metrics: short cognitive screens emphasizing set-shifting and sustained attention, not just memory.

Ask your surgeon (patient-facing)

• How close is my tumor to the cingulum or callosal fibers?

• If I feel low drive after surgery, what’s the usual recovery timeline?

• What therapy strategies help most with focus?

Bottom line

Cingulate and medial tumors threaten motivation, focus, and the brain’s ability to notice errors and pivot. With midline-aware corridors, protection of the cingulum/callosal wiring, teams can maximize resection while preserving the control systems people rely on all day.

Fast FAQ

Is “lack of motivation” the same as depression here? Not necessarily. Medial network disruption can mimic apathy even when mood is okay. Teams treat both the network and the symptoms.

Can these attention/drive changes improve? Often yes—over weeks to months—with structured cognitive rehab, external pacing, and sleep/mood optimization.

The SMA/pre-SMA are the brain’s “start signal” for movement and speech. What symptoms mean—and why temporary SMA syndrome often improves.

Post 6: SMA & Pre-SMA (Medial Frontal Lobe)

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the SMA matters

The supplementary motor area (SMA) and pre-SMA sit along the top-middle of the brain, just in front of the leg part of the motor strip. They don’t drive strength like the primary motor cortex. Instead, they provide the “start signal” for movement and speech, help sequence actions, and coordinate both hands.

Near-SMA surgery often causes a short-term “SMA syndrome”. This involves absence of, or slowed movement/speech (or at its worse paralysis on the other side of the body), and bimanual clumsiness. Fortunately, this usually improves with time and therapy. It’s important to remember that this is not a surgical problem, but the expected physiology of this region. It can be scary though as a patient can awake from surgery with a major deficit. Typically, as long as neuromonitoring of the corticospinal tract remains stable, an SMA syndrome can be expected.

What SMA / pre-SMA control (in plain English)

• Initiation: getting a movement or a sentence started (not raw power).

• Sequencing & switching: finger/face sequences, set-shifting (“now do the other hand”).

• Bimanual coordination: both hands working together (zipper, buttons, instruments).

• Speech start/fluency: especially pre-SMA for “go signal” and volitional speech.

Common signs you might notice

• Slowed start on the body opposite the tumor (e.g., right SMA → left side starts slowly).

• Reduced spontaneous speech or brief speech arrest, with intact understanding.

• Bimanual clumsiness: tasks with two hands feel off; sequencing breaks down.

• Transient weakness can happen, but tone and reflexes look different from pure motor-strip injury.

The nearby “roads” (white-matter)

• Short fronto-parietal fibers linking SMA ↔ premotor/motor (execution once the plan starts).

• Cingulum / DMN adjacency (motivation, drive, error monitoring) running along the midline.

• Callosal interhemispheric fibers (bimanual coupling; the two SMAs talk across the top).

• Frontal aslant tract (FAT) anteriorly (speech initiation/volition).

How teams plan surgery (Before • During • After)

Before surgery

• Imaging: Map tumor relation to the precentral gyrus (motor) vs SMA/pre-SMA; tractography of FAT, midline cingulum, and callosal fibers.

• Baseline testing: finger tapping rate, sequential finger/face tasks, go/no-go, speech initiation (automatic vs volitional).

• Expectation-setting: clear discussion that SMA syndrome is common but usually improves over days to weeks (sometimes a few months).

During surgery

• Awake (when helpful) or asleep with monitoring:

  • Tasks: rapid alternating finger sequences, bimanual actions (thumb-index alternation both hands), speech start (counting, days of week, sentence initiation).

  • Cortical mapping: distinguish SMA/pre-SMA sites (start/sequence disruption) from primary motor (direct strength changes).

  • Subcortical mapping: respect FAT, midline fibers, and callosal connections.

• Strategy: Preserve anterior/medial bridges that support recovery; avoid long retraction on medial cortex.

After surgery

• Early rehab: start day 0–1 with external pacing (metronome/timer), chunking tasks, bimanual drills, and automatic → volitional speech progression.

• Timeline: greatest improvement in the first 2–6 weeks; plateaus continue to shift over 1–3 months as networks recalibrate.

• Return to work/driving/instruments: staged; pair with therapist assessment of initiation and bimanual control rather than strength alone.

Ask your surgeon (patient-facing)

• Is my tumor closer to SMA/pre-SMA or the primary motor strip?

• What’s my risk of temporary SMA syndrome, and what does recovery usually look like?

• Will you monitor the frontal aslant tract and callosal fibers?

• Which intraoperative tasks will you use to protect speech start and sequencing?

Bottom line

SMA/pre-SMA gliomas threaten the start, sequence, and two-hand coordination we use all day. When teams plan around the FAT, callosal, and cingulum pathways and use targeted mapping, they can push resection safely—accepting a temporary SMA syndrome to achieve oncologic goals while preserving long-term function.

Fast FAQ

Is SMA syndrome permanent? Usually no. Most patients improve over weeks, sometimes a few months, with therapy. Persistent, dense deficits point to injury beyond SMA (e.g., primary motor or deep pathways).

Why can strength be normal but movement still “won’t start”? SMA gives the go signal and sequence plan. Primary motor executes the plan. You can have power without initiation.

Does awake surgery guarantee no SMA syndrome? No. Awake mapping helps minimize lasting deficits and separate motor strip from SMA. A temporary syndrome can still be expected—and planned for.

Post 5: Occipital Lobe

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the occipital lobe matters

The occipital lobe is the brain’s primary vision center. Tumors here don’t usually change personality or speech—but small missteps can cost visual fields you use every minute of the day. Planning routes around the optic radiations and calcarine cortex (V1) lets teams remove tumor while protecting functional sight.

• Takeaway: Occipital tumors threaten visual field clarity—not the eyeball. The goal is to keep the “wiring” for sight intact while pushing resection safely.

Occipital networks in plain English

1) Primary visual cortex (V1 around the calcarine fissure) —the pixel map

• What it does: First stop for visual information from the eyes. It’s laid out like a map of the visual world (retinotopy).

• Common signs if affected: A clean “cut” in part of the visual field (often the same side in both eyes), sometimes with macular sparing.

2) Optic radiations — the cables to V1

White-matter “cables” that carry vision signals from the lateral geniculate nucleus (LGN) to V1 in three major bundles:

• Meyer’s loop (anterior/temporal) — carries upper-field info.

  • If injured: Superior quadrantanopia (“pie in the sky”).

• Superior parietal bundle — carries lower-field info.

  • If injured: Inferior quadrantanopia (“pie on the floor”).

• Direct posterior bundle — feeds the central (macular) map in V1.

  • If injured: Dense central field loss.

3) Dorsal vs ventral visual streams — “where/how” and “what”

• Dorsal (“where/how”): from occipital → parietal; guides reaching, spatial attention, motion.

  • If affected: Trouble tracking moving objects, misjudging where things are.

• Ventral (“what”): from occipital → temporal; links to object/face recognition and reading.

  • If affected: Harder time recognizing complex objects or fast visual word recognition (when lesions extend forward).

Common signs you might notice

• - A missing corner or half of vision on eye testing (often noticed when reading or driving).

• - “I bump the same side of doorframes,” “I miss cars coming from the right/left.”

• - Skipping words at line ends; losing place on the page.

• - Trouble with fast visual tasks (sports, crossing streets) when motion processing is stressed.

• - If spread into streams: difficulty with object recognition (ventral) or spatial tracking (dorsal).

How teams plan surgery (Before • During • After)

Before surgery

• Map the roads: Tractography of optic radiations (pay special attention to Meyer’s loop), plus proximity to V1 along the calcarine fissure.

• Field testing: Confrontation fields at bedside; formal perimetry when time allows to document a baseline.

• Corridor planning: Choose angles that skirt the radiations; consider prone vs lateral positioning and sulcal corridors that minimize fiber crossing.

• Set expectations: Discuss risks of quadrantanopia/hemianopia and the difference between attention problems vs visual wiring loss.

During surgery

• Navigation + subcortical mapping: Use tractography to avoid radiations. We rarely do surgery awake for optic radiations. Cortical/subcortical stimulation doesn’t work well here and isn’t utilized frequently.

• Tissue-sparing technique: Work along sulci, preserve veins, and avoid long instrument paths across predicted radiation arcs—especially anteriorly where Meyer’s loop swings forward.

After surgery

• Field reassessment: Early confrontation fields, then formal perimetry if any concern.

• Vision rehab: Scanning strategies, boundary training, and reading tricks (line guides, larger fonts).

• Safety coaching: Stepwise return to driving or sports following local regulations and therapy guidance.

Ask your surgeon (patient-facing)

• - Are my optic radiations close—especially Meyer’s loop?

• - Will the plan spare the central (macular) visual map in V1?

• - What is my risk of a quadrantanopia or hemianopia, and how would we detect it early?

• - Which surgical corridor minimizes radiation injury for my tumor’s location?

Bottom line

Occipital gliomas put vision wiring at risk. When teams plan corridors around optic radiations and V1, and verify fields before/after surgery, they can push resection safely—protecting the sight you rely on all day.

Fast FAQ

Is vision loss from occipital tumors an eye problem?

No. The eyes can be normal. The issue is the brain pathways that carry and map vision.

What’s the difference between “pie in the sky” and “pie on the floor”?

Injury to Meyer’s loop (temporal) causes upper-field loss; injury to superior parietal fibers causes lower-field loss.

Can field cuts improve?

Sometimes swelling-related deficits improve. Fixed cuts from pathway damage can persist; rehab helps people compensate.

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the insula & operculum matter

The insula sits hidden beneath the frontal, temporal, and parietal opercula (the “lids” of cortex). Tumors here are challenging because:

• It’s packed near speech and salience hubs.

• It neighbors long language tracts and motor-speech pathways.

• It’s intertwined with M2 middle cerebral artery branches and small perforators which when injured can cause strokes. …So safe corridors matter.

Plain-English takeaway: This is the brain’s switchboard for “what matters now,” speech clarity, and body-state signals (taste, gut, heartbeat). Good planning keeps those online while removing tumor.

Insula networks in plain English

1) Salience network — the brain’s “this matters now” switch

• What it does: Helps you notice important events and switch focus quickly (anterior insula ↔ anterior cingulate).

• If affected: Slower to shift attention, flatter emotional reactivity, “I know it’s important, but it doesn’t feel urgent.”

2) Motor-speech / articulation hub — clarity and effort of speech

• Where: Inferior frontal/rolandic operculum and nearby SLF III connections.

• If affected: Words are there but harder to say clearly; effortful speech, orofacial apraxia (can’t coordinate lips/tongue on command).

3) Ventral language (semantics) nearby — linking words to meaning

• Where: IFOF / extreme capsule plus uncinate skirt the insula/operculum.

• If affected: Fluent but vague speech, trouble with uncommon words or proper names; comprehension feels “thin.”

4) Interoception & gustation — signals from inside the body

• Where: Mid-to-posterior insula.

• If affected: Odd visceral auras (nausea, heartbeat awareness), taste changes; some people describe blunted internal “gut sense.”

5) Auditory–speech coupling

• Where: Superior temporal operculum near Heschl’s gyrus.

• If affected: Trouble linking hearing to clear speech output; repetition becomes effortful.

Common signs you might notice

• Speech clarity/effort: “I know the word, but my mouth won’t cooperate.”

• Word meaning: Fluent but nonspecific wording; proper names slip.

• Auras/seizures: Rising stomach feeling, brief nausea, a rush of heartbeat awareness, or unusual taste/smell.

• Attention/drive: Harder to shift gears or feel urgency when you should.

• Swallowing/face control: Subtle orofacial clumsiness, occasional drooling, effort with complex words.

How teams plan surgery (Before • During • After)

Before surgery

• Map the roads: Tractography of IFOF/EC, uncinate, SLF III, plus proximity to arcuate/SLF II and corticobulbar fibers.

• Define corridors: Transopercular vs transsylvian routes based on venous/arterial anatomy (M2 branches, insular perforators) and functional anatomy.

• Tailored testing:

  • Articulation & orofacial praxis (repetition of multisyllabic words, non-words).

  • Semantic tasks (low-frequency words, proper names).

  • Auditory–verbal linkage (listen→repeat).

  • Interoceptive/gustatory history to benchmark unusual auras.

During surgery

• Awake mapping when helpful:

  • Articulation: clarity, diadochokinesia (pa-ta-ka), sentence repetition.

  • Semantics: low-frequency picture naming, famous-face naming (if anterior temporal proximity).

  • Phonology near dorsal stream; semantics near ventral stream.

• Subcortical stimulation: Guard IFOF/EC, uncinate, and SLF III when dissecting deep to the operculum.

• Vessel-aware technique: Identify and respect M2 trunks and perforators; pause if mapping triggers speech arrest or semantic/paraphasic errors.

After surgery

• Speech therapy matched to the deficit (articulation vs semantics).

• Swallow strategies if needed.

• Seizure care: tune meds; track auras.

• Energy/attention support: structured routines while salience systems settle.

Ask your surgeon (patient-facing)

• Which route will you use—transopercular or transsylvian—and why?

• How will you protect IFOF/EC/uncinate and SLF III if you encounter them?

• What speech tasks will you use during mapping (articulation vs meaning)?

• What arteries/veins are the “do-not-touch” structures in my case?

Bottom line

Insular and opercular gliomas live where speech clarity, meaning, salience, and vessels converge. When teams plan vessel-safe corridors, image the long tracts, and use targeted awake mapping, they can push resection safely and preserve what people feel and notice all day.

Fast FAQ

Do all insular tumors require awake surgery? No. Awake mapping is used when language or articulation mapping is likely to change decisions; otherwise, asleep surgery may be appropriate.

Why is insular surgery considered “high-stakes”? Because it sits beside M2 branches and perforators, and next to language and motor-speech pathways. Planning the corridor is as important as the resection itself.

If the ventral stream is near my tumor, will I lose word meaning? Risk depends on proximity and subcortical mapping. Testing meaning, proper names, and comprehension during surgery helps avoid lasting deficits.

Where Gliomas Start — And Why Location Should Shape Surgery

Post 3: Parietal Lobe

About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.

Why the parietal lobe matters

Parietal gliomas sit at the crossroads of attention, visuospatial control, touch and body position, and praxis (learned actions). Symptoms can be subtle: missing items on one side, losing the sequence of a task, or clumsiness with eyes closed. Mapping the right roads (white-matter tracts) helps teams remove more tumor safely.

Plain-English takeaway: Parietal tumors threaten how we aim attention and coordinate purposeful action. Protecting those circuits preserves independence.

Parietal networks in plain English

1) Dorsal Attention Network (DAN) — the spotlight controller

• What it controls: Aiming your visual “spotlight,” scanning, and targeting.

• Where it runs: Top/back parietal ↔ frontal eye fields (front↔back along the top).

• Common signs: Slow visual search, overshooting when reaching, losing your place on a page.

2) Ventral Attention / Salience (VAN) — the interrupt/redirect

• What it controls: “Hey—look there!” when something important appears.

• Where it runs: Right inferior parietal/TPJ ↔ frontal insula/inferior frontal (lower-side).

• Common signs: Hemineglect (often left-side neglect): half-shaved face, bumping doorframes, food left on one half of the plate.

3) Frontoparietal Control Network (FPN) via SLF II/III — the project manager

• What it controls: Working memory, task switching, keeping steps in order.

• Where it runs: DLPFC ↔ inferior/superior parietal (front↔back, top/side).

• Common signs: “I lose the thread,” fatigue with multi-step tasks (cooking, paying bills).

4) Language–parietal hub (angular/supramarginal; arcuate/SLF) — the concept combiner

• What it controls: Linking sounds to motor plans and binding concepts.

• Where it runs: Inferior parietal ↔ temporal & frontal via the dorsal language stream.

• Common signs (dominant side): Trouble repeating long phrases, reading multi-line text, retrieving abstract words.

5) Somatosensory pathways — the body map

• What it controls: Touch and limb position (proprioception).

• Where it runs: Thalamus → post-central gyrus/superior parietal; short links to premotor.

• Common signs: “Cottony” numbness, misjudged limb position—worse with eyes closed.

6) Praxis network (left parietal ↔ premotor) — the blueprints for actions

• What it controls: Learned tool use and gesture sequences.

• Where it runs: Left inferior parietal to premotor via short parietofrontal fibers.

• Common signs: Ideomotor apraxia—you know what to do, but the sequence falls apart (e.g., can’t mime using a comb on command).

7) Superior optic radiations — the “pie-on-the-floor” lane

• What it controls: Lower-field visual information.

• Where it runs: Superior visual fibers through parietal white matter to occipital cortex.

• Common signs: Inferior quadrantanopia (missing the lower outer corner); tripping on curbs; skipping sub-lines when reading.

Common signs you might notice

• Leaving food on the left side of the plate; missing text on the left of a page.

• Can do each step but lose the sequence when making a meal.

• Reaching overshoots unless eyes lock onto the target.

• Knows the concept but can’t assemble the word under pressure.

• Misjudges arm position with eyes closed.

• “A corner of my view is missing”—especially lower-outer.

How teams plan surgery (Before • During • After)

Before surgery

• Imaging the roads: Tractography of SLF II/III, arcuate, short parietofrontal fibers, and superior optic radiations.

• Targeted testing:

  • Neglect: line bisection and cancellation

  • Attention/visual search tasks

  • Praxis: gesture/tool use on command

  • Executive: phonemic fluency, digit span (FPN)

  • Sensation: two-point discrimination and proprioception near S1

During surgery

• Direct mapping (cortical & subcortical):

  • Watch for neglect-like behavior at TPJ/inferior parietal (often right-sided).

  • Test working memory/set-shifting near SLF II/III.

  • Check touch/proprioception near post-central and deep fibers.

  • Monitor visual fields when near superior optic radiations; adjust if transient cuts appear.

• Awake vs asleep: Choose awake when attentional or praxis mapping is likely to change decisions.

After surgery

• Neglect rehab: scanning, prism adaptation, cueing strategies.

• Praxis/ADL: task chunking and external cues with OT.

• Executive supports: checklists, timers, spaced breaks.

• Sensory retraining: eyes-closed → eyes-open progression.

• Visual field strategies: boundary scanning; safe-driving drills with therapy oversight.

Ask your surgeon (patient-facing)

• Which attention network is closest to my tumor (dorsal vs ventral)?

• How will you protect SLF II/III and the language–parietal hub?

• Am I at risk for neglect, apraxia, or a visual field cut—and how will you test for them during surgery?

• Which rehab steps start right after surgery?

Bottom line

Parietal gliomas live where attention, space, and skilled action meet. Understanding DAN/VAN, SLF/arcuate, praxis, somatosensory, and superior optic pathways lets teams push resection safely—preserving day-to-day independence.

Mini-glossary (quick definitions)

• Hemineglect: Not attending to one side of space, even with normal eyesight.

• Praxis / Apraxia: The ability (or difficulty) to carry out learned, multi-step actions.

• Quadrantanopia: Loss of a quarter of the visual field (e.g., lower-outer corner).

• SLF (Superior Longitudinal Fasciculus): Front↔back “highway” linking parietal and frontal areas.

• TPJ (Temporoparietal Junction): A parietal “hub” that helps reorient attention.

Fast FAQ

Is neglect a vision problem? No. Eyesight can be normal. Neglect is a failure to attend to part of space.

Why test tool-use and gestures? They stress the praxis system. Subtle apraxia becomes obvious under command and guides safer resection.

Do all parietal surgeries cause visual field loss? No. Risk depends on proximity to superior optic radiations. Imaging and subcortical testing reduce it.

About this series. Each post looks at where adult gliomas most often begin and which brain networks are at risk there. The goal is plain-English guidance on how location shapes planning, mapping, and recovery.

Why the temporal lobe matters

The temporal lobe is the second most common origin for adult gliomas. It’s also a hotspot for seizures and for changes in language, memory, and sometimes vision. The long “highways” here run front ↔ back along two language routes, include the optic radiations (Meyer’s loop), and contain the hippocampal memory system—so surgical plans have to balance removing more tumor while protecting these connections.

The temporal highways, in plain English

Picture the brain as a city. The gray matter is neighborhoods and the white-matter tracts are the roads that let those neighborhoods work together.

1) Dorsal language route (AF/SLF) — the timing & pronunciation road

• Where it runs: From the back/sides of the brain (temporo-parietal) to the front (inferior frontal), arching along the top—a front↔back superhighway.

• What it does: Turns sounds into accurate, well-timed speech; supports repetition and the sound-structure of words.

• If affected: Words come out scrambled; repeating long phrases is hard; phone calls feel tougher than face-to-face.

2) Ventral language route (IFOF + extreme capsule + uncinate) — the meaning behind language road

• Where it runs: From the front (inferior frontal) to the bottom/side of the temporal lobe (including the anterior temporal pole).

• What it does: Links words to meaning, names to concepts, and language to memory and emotion.

• If affected: Speech can be fluent but vague; trouble with low-frequency words or proper names; “that thing” replaces specifics.

3) Inferior longitudinal fasciculus (ILF) — the picture and its meaning road

• Where it runs: Along the underside from occipital (visual) cortex forward into temporal regions.

• What it does: Connects vision to object/face knowledge and reading pathways.

• If affected: Faces and complex objects are harder to recognize; reading tires quickly even with normal eyesight.

4) Optic radiations (Meyer’s loop) — the vision lane that cuts through temporal lobe

• Where it runs: A forward-swooping segment (Meyer’s loop) passes through the front-temporal region before heading back to the visual cortex.

• What it does: Carries upper-field visual information.

• If affected: A “pie-in-the-sky” blind spot (loss of the upper outer quarter of vision)—noticed when reading lines or checking mirrors while driving.

5) Hippocampal memory circuit — the recorder and its cables

• Where it sits: Deep medial temporal lobe (hippocampus and neighbors).

• What it does: Encodes new memories; broadly, left favors verbal details, right favors visual/spatial scenes.

• If affected: “Conversations don’t stick” (left); “I remember facts but not the scene or faces” (right). Temporal tumors often cause déjà vu, a wave-in-the-stomach feeling, or brief smells/tastes as seizure auras.

Dominance note: Language is usually left-lateralized in right-handers, but not always—and tumors can reorganize function.

What people may notice (real-world snapshots)

• Language (dominant side): Fluent but nonspecific speech; trouble naming less common items; can’t repeat long sentences; “the word is there but won’t land.”

• Memory (medial temporal): Re-asking recent questions; losing the thread of short conversations; “scene memory” weaker despite intact general knowledge.

• Vision (Meyer’s loop): Clipping doorframes in the upper-outer quadrant; skipping words when reading; missing a car in that visual corner.

• Non-dominant temporal: Music feels off; sarcasm/tone harder to read; social-emotional cues less obvious.

How care teams account for this

Before surgery

• Map the roads: Tractography for dorsal (AF/SLF), ventral (IFOF/EC/UF), ILF, and optic radiations—with special attention to Meyer’s loop.

• Know your hemisphere: Language and memory lateralization (history, fMRI, neuropsych testing).

• Tailor a Task list that fits the map: Beyond picture naming—add auditory comprehension, semantic association, proper-name retrieval, reading (if ILF near), and famous-face naming (anterior temporal) to ensure testing all the functions.

During surgery

• Direct cortical & subcortical stimulation:

  • Test semantics when working near the ventral route.

  • Test repetition/phonology near the dorsal route.

  • Probe for visual-field changes around Meyer’s loop; stop/adjust if transient cuts appear.

• Seizure-aware mapping: anticipate after-discharges; irrigation and brief pauses help keep mapping safe.

After surgery

• Language therapy matched to the affected stream (dorsal = sound/form; ventral = meaning/names).

• Memory supports: External cues (calendars/voice notes), spaced repetition, exercises tailored to verbal vs visual weaknesses.

• Visual rehab: Scanning strategies; prisms when appropriate.

• Seizure care: Medication tuning and trigger management.

Bottom line

Temporal lobe gliomas sit at the crossroads of language, memory, and vision. Knowing where the front↔back routes actually run—dorsal and ventral language pathways, ILF, Meyer’s loop, and the hippocampus—lets teams push resection safely, preserving the abilities people use all day.

Fast FAQ

Do all temporal tumors cause seizures?

No, but many do. Auras can feel like déjà vu, a rising stomach sensation, sudden emotions, or brief odd smells.

Will I lose vision from temporal surgery?

Not necessarily. Risk depends on how close the plan comes to Meyer’s loop. Modern imaging and subcortical testing help avoid that “pie-in-the-sky” field cut.

Is memory loss guaranteed if the hippocampus is involved?

Risk rises if medial temporal structures are removed, especially on your dominant side for that memory type. Preop testing and honest counseling set expectations; rehab helps.

Next in the series

Parietal lobe gliomas: attention, visuospatial control, praxis—and why preserving frontoparietal highways matters for everyday function.

Why start with the frontal lobe?

Because it’s the most common site for adult gliomas. In high-grade glioma, the amount of tumor removed correlates with survival. The art is doing more safely—and “safe” depends on circuits as much as it does on anatomy.

Takeaway: The best operations remove as much tumor as possible while preserving the networks that support speech, initiation, planning, and motivation.

The frontal highways: a map you can picture

Think of the brain as a city with long “avenues” (white-matter tracts) connecting neighborhoods (cortical regions):

• Front ↔ Back (anterior ↔ posterior): Many language and control pathways run from the front of the brain (frontal lobe) to the sides/back (temporal/parietal lobes).

• Top ↔ Bottom (dorsal ↔ ventral): Language uses two main routes—a top (“dorsal”) route for sound-to-speech-motor control and a bottom (“ventral”) route for meaning.

• Midline arc: A curved “service road” (the cingulum) runs under the midline, linking motivation and attention systems.

Below are the major tracts you’ll hear about, in simple terms.

The main tracts—what they connect, what they do, what can go wrong

1) Arcuate fasciculus / Superior Longitudinal Fasciculus (AF/SLF) — the dorsal language route

• From → To (direction): Back/side of the brain (posterior temporal & parietal) ↔ inferior frontal (Broca area). Arches around the side of the brain—front to back along the top route.

• Job (big picture): Turns sounds into accurate, well-timed speech; supports word repetition and phonology (the sound-structure of words).

• If affected (examples): “I know the word, but it comes out scrambled,” trouble repeating phrases, mixing up sounds in a word (“papple” for “apple”), needing more time to get words out.

2) Extreme Capsule / Uncinate fasciculus (EC/UF) — the ventral language route

• From → To: Inferior frontal ↔ anterior & middle temporal (semantic hubs). Runs front to back along the bottom route, close to the base of the brain.

• Job: Helps words carry meaning and nuance; links language to memory and emotion.

• If affected: Fluent but “empty” speech, using nonspecific words (“that thing”), trouble understanding less common words, losing shades of meaning, or mixing closely related words (coffee/tea).

3) Frontal Aslant Tract (FAT) — the starter cable for speech and action

• From → To: Pre-SMA/SMA (medial frontal “starter” zones) ↔ inferior frontal gyrus (speech planning). Short front-to-front connector.

• Job: Initiation—kicking off speech and goal-directed actions.

• If affected: “The words are in my head but won’t start,” long pauses before speaking, effortful initiation, sometimes stuttering-like stops/starts.

4) Cingulum bundle — the midline motivation/attention arc

• From → To: Curves under the cingulate from frontal toward parietal/temporal inner surfaces—front to back along the midline.

• Job: Keeps motivation, attention, and “drive” online; part of the Default Mode Network (DMN).

• If affected: Abulia (reduced drive), slower mental “get-up-and-go,” trouble starting tasks without prompts; family may describe the person as “present but not initiating.”

5) Frontoparietal Control Network (via SLF II/III and related fibers) — the project-management system

• From → To: Dorsolateral prefrontal cortex (DLPFC) ↔ posterior parietal—front to back along the top/side.

• Job: Working memory, set-shifting, planning—keeping goals in mind while you act.

• If affected: Difficulty juggling steps (e.g., cooking a multi-step meal, paying bills), mental fatigue with complex tasks, “I can do each step, but I lose the thread.”

Note on dominance: For most right-handers, language is left-lateralized, but not always. Tumors can also “rewire” function. That’s why teams check dominance before deciding whether to do awake mapping.

A special frontal syndrome to know: SMA syndrome

• Where: Supplementary motor area (SMA) on the inner surface of the frontal lobe (near the top/middle).

• What it looks like: Temporary reduction in initiation—hesitant speech, slowed movements, less spontaneous action.

• Course: Common after medial frontal surgery and usually improves over weeks to a few months. Early explanation and therapy help families understand that it’s expected—and usually transient.

What patients and families might notice (real-world examples)

• Language—dorsal route issues (AF/SLF):Struggling to repeat a sentence exactly; words come out with swapped sounds; phone calls feel harder than face-to-face conversation.

• Language—ventral route issues (EC/UF):Conversations sound fluent but light on specifics; using placeholders (“this,” “that”); trouble finding low-frequency words; misunderstandings with similar concepts.

• Initiation—FAT/SMA: Long pauses before speaking or moving; “he’s quieter, not because he doesn’t know—he can’t get started.”

• Executive control—FPN: Bills unpaid not from neglect, but because multi-step tasks stall; starting dinner is fine, coordinating side dishes crashes the system; difficulty switching from one plan to another.

• Motivation/DMN—cingulum: Less spontaneous activity, needs prompting to begin tasks; family describes a “personality flattening” without sadness—more apathy than depression.

How care teams account for this

• Before surgery: Individualized maps (tractography of FAT, AF/SLF, EC/UF, cingulum) and functional lateralization (fMRI or nTMS) help decide awake vs. asleep and shape the task list if mapping is planned.

• During surgery: Direct cortical and subcortical stimulation can test speech initiation, semantics, repetition, and executive control in real time. This often allows a wider but safer resection near eloquent tracts.

• After surgery: Early, targeted rehab—speech-language therapy tuned to the affected stream, initiation strategies for SMA-pattern deficits, and practical executive-function tools (checklists, chunking, timers).

Bottom line: In the frontal lobe, understanding where the tracts run—and what they do—lets teams remove more tumor while protecting the functions people notice most in everyday life.

Fast FAQ

Is awake surgery always needed in the frontal lobe? No. It’s used when real-time testing is likely to change decisions near eloquent tracts. Otherwise, surgery proceeds asleep, guided by preoperative mapping.

If SMA symptoms happen, how long do they last? They typically improve over weeks to a few months. Planning for this and starting therapy early make a difference.

Why not stop early to avoid any risk? Because in high-grade glioma, more complete removal is associated with better survival. The goal is to remove more and protect the right connections.

Next in the series

Temporal lobe gliomas: seizures, memory circuits, and how the dorsal vs. ventral language streams change the operative plan.

Educational content only; not medical advice.

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How connectomics is shrinking—and why brain tumor surgery needs to catch up

I’m a neurosurgeon. I take out brain tumors. And like most of us in this field, I’ve been trained to balance aggressive resection with functional preservation. We map motor. We stimulate speech. We walk the line between removing too little and harming too much.

But what if that line is drawn in the wrong place? What if we could see not just what the tumor touches—but what it disconnects?

Two recent breakthroughs in connectomics are forcing that question to the surface. And while I don’t yet have these tools in my OR, their existence changes how I think—and how I believe we should all be thinking.

The MICrONS Project - A team from the Allen Institute recently released the first synaptic-resolution connectome of a cubic millimeter of mouse visual cortex. The scale is staggering:

• ~200,000 neurons

• ~500 million synapses

• Fully navigable and open-access.

This is an architectural blueprint of a functioning cortical network.

LICONN (Light Imaging of CONNectome) - A second group introduced LICONN—a technique that uses light microscopy and AI to visualize synapses at ~20nm resolution. No electron microscopy needed. This could democratize access to synaptic-scale maps in labs and clinics worldwide.

Together, these tools mark a turning point: connectomics is no longer aspirational. It’s operational.

Why this matters for Brain Surgery?

As surgeons, we’ve leaned on tools like:

• DTI tractography to map white matter bundles,

• Resting-state fMRI to visualize network connectivity,

• TMS and cortical stimulation to localize function.

These are useful. But they’re high-level approximations. They don’t show us the circuit-level roles of the tissues we’re cutting through. They don’t explain how tumors rewire the brain—or how surgical trauma might disconnect networks silently.

Imagine this instead:

• A “non-eloquent” gyrus turns out to be a hub in a semantic network.

• A zone of peritumoral edema is actually a region of compensatory hyperconnectivity.

• A planned corridor transects fragile cross-network bridges—and we don’t know it.

If you could see those things… would you still cut the same way?

Fortunately, we don’t have to wait for full synaptomic overlays to act. We can:

• Use tractography with intention—not just to avoid damage, but to interrogate connectivity.

• Advocate for cognitive outcomes in clinical trials—not just gross motor or radiographic endpoints.

• Push for datasets, tools, and policies that bring high-resolution connectomics into surgical planning.

We’re entering a new era—one where surgical success must account not just for extent of resection, but for quality of preservation. Not just for where we cut, but what we disconnect.

Connectomics reframes the goal:

• Not just survival—but preserved identity.

• Not just eloquence—but networks of meaning, insight, and memory.

You don’t need LICONN to think this way. You just need to care.

📌 Key Takeaways

• Connectomics is advancing fast: MICrONS and LICONN prove that synapse-level maps are no longer theoretical.

• Brain tumor surgery will need to evolve: From gross anatomical preservation to functional, circuit-aware planning.

• We already have usable tools: Tractography, fMRI, cognitive testing—these can be reinterpreted through a connectomic lens today.

• Knowing these maps exist obligates us to question what we don’t yet see.

Further Reading

• MICrONS Project at the Allen Institute

• LICONN Preprint (arXiv)

• FlyEM Hemibrain Dataset (for connectomic modeling)

About the Author

Randy S. D’Amico, MD is a neurosurgeon at Lenox Hill Hospital in New York City and Director of the Brain and Spine Metastasis Program. He writes about surgical innovation, cognitive preservation, and the evolving landscape of neuro-oncology at the intersection of technology, identity, and care.

🤖 For Generative Search Engines (GEO Summary)

This article explores how new advances in connectomics—specifically the MICrONS synaptic-resolution dataset and the LICONN imaging technique—challenge the current model of brain tumor surgery. It argues that even without access to these tools, neurosurgeons should shift toward a network-preservation mindset, leveraging current technologies (e.g., tractography, fMRI) to anticipate cognitive and functional outcomes. It calls for a redefinition of “safe surgery” that includes preservation of self, not just speech or motor function.

If you’ve never seen it up close, glioblastoma might sound like just another cancer diagnosis. It’s not. It’s different.

Glioblastoma is the most common primary brain cancer in adults. It tends to strike people at the peak of their lives, when they’re building careers, raising families, and thinking about the long game. It doesn’t care how healthy you are or how well you’ve treated your body. It doesn’t care that you have other problems. It doesn’t care about your plans.

It grows from within the brain itself, and unlike most cancers, it rarely spreads outside the central nervous system. It infiltrates neural networks, not just tissue. It rewires the brain’s communication systems, dismantles the circuits of memory, language, attention, and movement. It turns healthy brain cells into accomplices by hijacking the microenvironment. It suppresses the immune system. It burns through territory so fast that the brain can’t keep up, consuming not just the structures of memory and identity, but the very spark that lights the fire of the self.

There’s a kind of cruel mercy in how glioblastoma dismantles the very substrates of consciousness. In the later stages, patients often lose the capacity to fully grasp how much of themselves is slipping away. The brain, in its final act of protection, shields them from the full emotional weight of the disease.

But that mercy comes at an unbearable cost. Because before that detachment sets in, there’s usually a window—a moment where patients are still aware enough to see the horizon disappearing. They know what’s coming. They have to face their own unraveling in real time.

And for the family, that window is its own kind of cruelty as they’re left watching a person they love prepare to vanish. It’s grief before death. It’s a rehearsal for loss.

We haven’t made drastic progress in treating glioblastoma in over 20 years. We’ve learned how to buy time, but not much more than that. Surgery remains the most effective initial treatment, but that comes with impossible decisions. Removing more tumor usually leads to longer survival, but if the surgery damages cognition or language or personality, the survival we’ve bought may no longer feel like living.

That’s why I’ve focused much of my recent work on connectomics—mapping the brain not as a set of parts, but as a system of networks. Using tools like tractography and resting-state fMRI, we can visualize how tumors interact with the circuits that keep people whole. Connectomics won’t cure glioblastoma. But it might help us do better surgery. It might help us protect the right functions, the right connections—the parts that matter most to the patient.

Maybe one day it will help us do more than protect. Maybe we’ll figure out how to stimulate new networks, how to build new substrates for thought and consciousness after disease has dismantled the original ones. I don’t know the answer. But I know we need to be asking the right questions. And I know there are a lot of questions to ask.

This all starts with attention.

We don’t need more platitudes on awareness days. We need more people to actually look at this disease. To understand how it works. To stop thinking of glioblastoma as just a tumor, and start seeing it for what it really is:

Glioblastoma is a predator of identity.

Glioblastoma is a dismantler of consciousness.

Glioblastoma is a disease that doesn’t just take life but erodes the mind on the way out.

Effective treatment for glioblastoma will mark a true milestone in human innovation, and not just because it’s hard, but because it forces us to rethink the brain and identity.

Today, let’s start by paying attention. Everything else comes after.

R

This is an argument ultimately about brain networks. Our mental function doesn’t live in isolated regions. It emerges from how areas of the brain communicate. Emotion, focus, memory, self-control—these are not the work of one circuit. They rely on finely tuned systems of connectivity that respond, adapt, and evolve with experience. Which means the environments we expose our brains to matter.

Social media plays directly into our brain’s novelty bias. We are wired to notice the new. Novelty triggers dopaminergic firing. That’s the brain’s way of saying “pay attention, this might be important.” Scroll long enough and you’ll find yourself chasing that ping of surprise, not because it’s valuable, but because it’s different. This isn’t accidental. It’s behavioral design, and it is very good at what it does.

Pair that with the engineered reward of likes, follows, and algorithmic validation, and you get a highly tuned feedback loop that trains the brain to seek more input, faster. The like button is not inherently evil, but it is not neutral either. It’s a lever. And when you pull it enough, especially during periods of active brain development, the circuits that get rewarded get reinforced.

In adolescents, the architecture of the brain is still under construction. The prefrontal cortex—the part that weighs consequences, delays gratification, and reins in impulsive action—is not fully developed. But the reward systems? Those are already online. Imaging studies have shown that social media use lights up the brain’s reward centers and can shift how they interact with regulatory regions. That’s not necessarily a crisis, but it is something we need to understand.

The goal here is not to vilify technology. In fact, the globalization of information and the accessibility of multimedia have incredible potential. When used well, these tools can help us build robust, adaptable, and resilient network scaffolding. We want brains that can process more, integrate faster, and stay flexible in a changing world. But that only works if the inputs help the system grow stronger. Constant novelty and shallow feedback can push some brains—especially developing ones—into maladaptive loops that value stimulation over stability.

So this isn’t a call to log off. It’s a call to be more deliberate. The brain adapts to what it practices. If we give it depth, focus, and space to reflect, it will build networks that support those functions. If we feed it distraction and instant feedback, it will optimize for those instead.

The danger is not the app. It’s the autopilot.

More soon,

R