Chapter 9: The Subcortex and Psychosurgery

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You know, when you look at a map of the human brain,

it's incredibly easy to get completely mesmerized by the cerebral cortex.

Well, absolutely.

It's the part everyone recognizes.

Right.

That wrinkly folded outer layer is,

it's the glamorous part of the brain.

I mean, it's where language and conscious thought and your entire personality basically seem to live.

Yeah.

It's essentially the penthouse suite of human existence.

Exactly.

But you know, you can't have a penthouse without a solid foundation.

And today we're going down into the basement.

Which is where you find the foundational structures that keep the whole building standing.

I mean, if the basement floods, the penthouse loses power.

That is perfectly put.

So welcome to this deep dive.

Today we are taking a stack of neuropsychology research.

Specifically, we're pulling from chapter nine of the foundational text, Introduction to Neuropsychology, second edition.

Right.

And we are descending into the subcortex.

We're going to look at the hidden engine room of our consciousness, and then we'll explore the highly complex and

sometimes really controversial ways medical science has tried to physically alter it.

It's a heavy topic, but it's fascinating.

Okay.

Let's unpack this.

Why is the subcortex so mysterious compared to the wrinkly cortex up top?

I mean, it seems like we know far less about the basement than the penthouse.

Well, it really comes down to the sheer mechanical difficulty of studying it in humans.

How so?

So in neuropsychology, you learn how a brain part works by observing patients who have localized damage, right?

A lesion in that specific area.

The classic lesion method.

Exactly.

But subcortical lesions in humans are just incredibly rare to find in isolation.

If a patient develops a tumor deep in the brain, a surgeon usually has to cut through and disturb the overlying healthy cortex just to reach it.

Oh, I see.

So that instantly muddies the waters.

Exactly.

You can no longer tell if a cognitive deficit was caused by the deep tumor itself or by the surgical path they had to take to get down there.

Wow.

Yeah.

And I imagine traumatic injuries like a severe blow to the deep brain are a whole different story.

Oh, they're very often fatal.

The structures down there, they govern the absolute baseline requirements for life.

So it's not just about memory or language?

No, not at all.

If a severe injury isn't fatal, the effects on basic survival behavior are usually so radical and debilitating that we can't even begin to assess the patient's higher cognitive abilities.

Right.

Like you can't test the vocal fluency of someone who is literally just fighting to maintain a heartbeat.

Precisely.

So we're left with a real challenge.

So if human lesions are either muddy or fatal, how do we actually map this out?

Where does the text say our baseline knowledge comes from?

We rely heavily on animal studies.

And I know you might hesitate to compare a human mind to your rat's brain.

Yeah, it feels like a big leap.

It does.

But the clinical evidence we do have from humans shows that when it comes to the lower, more primitive functions of the subcortex, those generalizations from animal models to humans are

surprisingly accurate.

Okay, that makes sense.

Let's start at the very bottom then at the brain stem, specifically looking at the ascending reticular activating system or AER -S.

The AER -S.

From the text, this is essentially the main power switch for the whole brain.

It is.

It dictates your overall level of consciousness, your attention, and just general awareness.

Think of it as the

neurologist will tap your knees and check your reflexes with such care.

Exactly.

Those peripheral bodily reflexes are a direct window into the health of these deep activating systems.

Oh, wow.

Yeah.

And if a patient suffers a lesion in the lower brain stem, the engine just cuts out entirely.

They might suffer sudden attacks of deep, unarousable unconsciousness.

There's also a very specific, almost haunting symptom tied to lower brain stem damage that the book mentions, called chain -stokes breathing.

Right.

That is a very distinct respiratory pattern.

What does that look like, practically?

Because the lower brain stem is basically failing to smoothly regulate the body's carbon dioxide levels, the breathing becomes slow, deep, and periodic.

It waxes and wanes.

You see this heavily in deep coma states.

That is chilling.

But the text contrasts that deep coma with lesions slightly higher up, right, in the upper brain stem and around the thalamus.

Yes.

Damage higher up produces states that look much more like sleep.

Like actual sleep.

Sort of.

It might be a sleep that is short and fitful, but it's fundamentally different from the deep, profound unconsciousness caused by lower brain stem damage.

Okay.

I want to synthesize this visually for everyone listening.

If the subcortex is the basement,

I picture the internal capsule and the pyramidal tracks as these massive bundles of elevator cables.

That's great analogy.

Right.

They are carrying all the sensory signals from your body up to the penthouse, the cortex, and carrying the movement commands back down to the spinal cord.

Exactly.

They're the critical pathways.

So if those elevator cables snap in the basement, the penthouse is completely isolated.

The cortex could be perfectly healthy, perfectly normal, but the signals, they have nowhere to go.

If those cables are severed, the system basically crashes.

A lesion in the internal capsule or those pyramidal tracks will severely paralyze patients' somatosensory and motor performance.

Even if the cortex is fine?

Even if it's completely untouched, they simply can't move or feel normally, even though the outer wrinkly cortex where the actual intent to move originates is perfectly healthy.

Wow.

Okay.

Since we're tracking these elevator cables upward from the brain stem, they eventually pass through the midbrain and into the thalamus.

Yes.

Moving up the chain.

And, you know, you might traditionally think of the thalamus as just a lobby switchboard, right?

Yeah.

Just routing sensory information to the right department.

That's the common assumption, yeah.

But the text notes that damage here leads to severe motor disabilities.

We're talking resting tremors, involuntary, unpredictable body movements called coreiform movements.

And dystonia, that uncontrolled twisting.

Right.

Parkinsonian symptoms are deeply tied to this area.

But wait, I want to push back on something here.

Okay, go for it.

If the thalamus is just a relay station for sensory and motor signals, does it actually play a role in higher level thinking like cognition?

It absolutely does.

And this completely shatters that idea of a simple relay station.

The thalamus is actively processing information.

Really?

How do we know that?

Well, we know from a pivotal 1978 study by Wilke that phalamic lesions actually alter higher cognitive performance.

And it depends entirely on which side of the brain the damage is on.

Oh, interesting.

Yeah.

Lesions on one side of the thalamus will impair a patient's verbal fluency, while lesions on the other side will disrupt their ability to recognize and match human faces.

Wait, so laterality matters even deep in the basement?

It really does.

And to understand how they prove this, without just relying on accidental lesions, you have to look at the work of Fideo and Van Buren from 1975.

What did they do?

They chronically implanted tiny electrodes into a specific region of the thalamus called the pulvinar.

Okay.

By running a mild electrical current to stimulate that exact spot, they could induce temporary dysphagia in the patient, meaning the patient suddenly had difficulty speaking or understanding language.

Just from stimulating the thalamus.

Exactly.

The stimulation also triggered temporary memory loss and poor visual discrimination.

And once the current stopped, the deficits just vanished.

That is wild.

There's also a quirky anacomical detail in this chapter that I find fascinating.

There's this small bridge of tissue called the massa intermedia, which connects the left and right halves of the thalamus.

But here's the catch, not every human being has one.

And research from Lansdale and Clayton Davies in 1972 suggested that the structural absence of this massa intermedia might actually be associated with higher intelligence in males.

Which is just a brilliant example of how much structural variation exists from person to person.

Yeah.

We're not all built exactly the same.

Right.

And while the scientific community is always careful to note that not all of these functional relationships are set in stone, it proves that vast amounts of cognitive nuance are hiding in these deep, supposedly primitive structures.

Okay.

So if the thalamus is routing signals, what structure is actually generating the raw primitive drives behind our behavior?

That takes us slightly down and forward to the hypothalamus.

The master regulator.

Exactly.

It runs your autonomic nervous system and governs the base drives eating, drinking, sleeping, and sexual behavior.

And the research points out a very specific real world consequence of damaging this area, right?

The impotence that sometimes affects veteran boxers.

Yes.

Think about the physics of a boxing match.

The brain is suspended and fluid.

So when a boxer takes repeated heavy rotational blows to the head, the brain twists inside the skull.

Just picturing that is awful.

It is.

Those shearing forces stretch and tear the delicate vascular and neural connections at the very base of the brain, heavily impacting the hypothalamus.

Oh, it's a stark reminder of the mechanism.

Physical mechanical trauma directly alters fundamental human drives.

Exactly.

But those basic drives don't operate in a vacuum though.

They need to be linked to your memories, your emotions, your actions.

This is where the basal ganglia comes into play, isn't it?

It is.

The basal ganglia is deeply connected to the temporal lobe.

It acts as a bridge between your physical movements and your emotional states, things like memory and crucially, aggression.

That's a huge link.

It really is.

That intersection between the motor loops and the emotional loops within the basal ganglia is vital.

It helps explain why later on we'll see surgeons targeting deep brain structures to treat severe behavioral issues.

The brain does not neatly separate a physical movement from the emotion driving it.

Right.

And finally, to execute any of these drives physically,

you need precise coordination.

Enter the cerebellum.

Yes, the cerebellum sits at the back of the brain and acts as the ultimate supercomputer for motor coordination, balance, and position sense.

Basically crunching the numbers for movement.

Exactly.

It calculates the millions of tiny micro adjustments your muscles need to make every single second.

So what happens if there's a damage to the cerebellum?

They'll show tremor and jerkiness, specifically when trying to execute intentional movements like reaching for a cup.

Oh, okay.

They'll also walk with a very broad -based gait, almost in a drunken fashion, because the system that normally computes their center of gravity is essentially offline.

Wow.

Okay, so let's step back.

What does this all mean?

It means these deep structures govern literally everything from how we walk to our sexual drives, to our fundamental state of consciousness.

The absolute core of our being.

Right.

And treating disorders in these hidden areas requires highly precise, highly invasive physical interventions,

which brings us to the blurry and heavily debated world of brain surgery.

A very complex topic.

Yeah.

Okay, let's unpack the terminology because reading the text, what is the actual difference between neurosurgery, which is universally accepted medical practice, and psychosurgery, which is intensely controversial?

What's fascinating here is, well, the distinction actually falls apart under scrutiny.

Really?

How so?

The traditional claim is that neurosurgery removes diseased pathological tissue to correct a physical abnormality, whereas psychosurgery destroys healthy normal tissue simply to alter a patient's mental symptoms.

But wait, routine neurosurgeons destroy healthy tissue all the time, don't they?

They do.

They routinely destroy perfectly healthy brain tissue to relieve severe spasticity in a patient's limbs or to relieve intractable chronic pain.

And pain is fundamentally a purely mental phenomenon.

Exactly.

Furthermore, the physical symptoms of a brain tumor might only manifest as cognitive or emotional changes.

So the dividing line between what is a physical disease versus a mental symptom or what is healthy versus diseased tissue is largely artificial.

So it's more about

Yes.

The distinction is truly based on what society currently accepts as standard medical practice versus what it finds ethically controversial.

Which is why some proponents argue we should just call all of it psychiatric surgery and be done with it.

But this brings up a massive misconception that you, as a student reading this text, might have.

The assumption about drugs versus surgery?

Yes.

It is so easy to assume that pharmaceutical drug treatments are safe, gentle, and easily reversible, while brain surgery is crude, dangerous, and permanently terrifying.

And that is a dangerous oversimplification.

Psychotropic drugs are incredibly potent chemical shotguns.

Chemical shotguns.

I like that.

Yeah.

They are notoriously non -selective, meaning they don't just hit the specific brain circuit causing the problem.

They bathe the entire brain and body in chemicals, bringing a cascade of unwanted side effects.

Which often require a of even more drugs to manage.

Exactly.

And crucially, long -term drug use can cause highly irreversible neurological damage.

There's actually a striking clinical example of this in the chapter regarding older adults with a history of coronary disease.

Yes.

The ECT example.

Right.

For these patients, it's often considered much safer to administer electroconvulsive therapy ECT than to put them on certain antidepressant drugs.

Wait.

Why is that?

Because shocking the than just taking a pill.

It does sound that way, but it's because of the underlying cardiovascular mechanisms.

Antidepressants can cause severe unpredictable drops in blood pressure and dangerous cardiac arrhythmias.

Which can be fatal for someone with a weak heart, precisely.

ECT, on the other hand, is performed under general anesthesia.

The physical stress on the cardiovascular system can be tightly monitored, controlled, and managed by an anesthesiologist minute by minute.

Ah.

Surgery and physical interventions are hazardous and irreversible, yes, but we absolutely cannot pretend drugs are a perfectly safe, consequence -free alternative.

That makes a lot of sense.

So let's look at how surgeons actually physically intervene in the subcortex, starting with uncontroversial applications for Parkinson's disease.

Right.

Which involves severe dysfunction in the basal ganglia.

To treat this, surgeons developed something called stereotactic surgery.

What does that involve?

Stereotactic surgery relies on incredibly precise three -dimensional brain maps.

The surgeon inserts long, thin probes deep into the brain, navigating via external landmarks on the skull and advanced imaging.

Okay, that sounds highly technical.

It is.

The initial insertion of the probes happens while the patient is under general anesthesia.

But here is the critical mechanism.

Once the probes are in place, the anesthesia is lifted and the patient is brought back to full consciousness.

Wait, pause.

They bring the patient out of anesthesia with surgical probes actively resting inside the core of their brain.

They do.

How does a patient not panic, and how do they even test them?

Well, the brain itself has no pain receptors, so the patient feels absolutely no pain from the probe.

Oh, okay.

They have to wake the patient up because human anatomy varies slightly from person to person.

The surgeon sends a tiny reversible electrical current through the probe to stimulate the tissue.

Just to see what happens.

Exactly.

They watch the patient's physical reactions and ask them questions to guarantee the probe is resting on the exact microscopic target before they create a permanent lesion.

Wow.

And once they confirm the target?

Usually areas like the ventrolateral nucleus of the thalamus or the globus pallidus.

They deliberately destroy that tiny pocket of tissue using high -frequency coagulation, freezing, or precise radiation.

And what are the results of essentially burning out a circuit in the basement?

Historically, for specific symptoms, the results were remarkable.

In about nine out of ten patients, it completely abolished the severe resting tremors and rigidity.

Nine out of ten.

That's incredible.

It is, but there's a catch.

It largely failed to improve akinesia, which is the neurological difficulty in initiating a motor act.

Right.

Because creating irreversible lesions didn't cure all everyday functions and carried risks to speech, this specific lesion -making approach actually declined.

Today, drug treatments like levodopa are preferred, alongside modern deep brain stimulation or DBS.

Which uses a pacemaker to regulate the electrical signals without having to destroy the tissue, right?

Exactly.

Much safer.

We also see uncontroversial tissue removal for focal epilepsy.

If a patient has a specific focal point in the brain, a surgeon can simply remove that epileptogenic tissue.

And the outcomes here are very strong.

For lesions that are not tumors, about two -thirds of patients see a marked reduction in their seizures.

That's significant.

Yeah.

And about a third become completely seizure -free forever.

Operative mortality is extremely low.

When you weigh that against the fact that heavy anti -convulsive drugs can seriously retard a patient's cognitive function over a lifetime, the surgical alternative becomes highly attractive.

A very specific form of this is the anterior temporal lobectomy.

Yes.

To safely remove part of the temporal lobe without destroying the patient's ability to speak, surgeons use something called the WADA technique.

How do they actually do that?

The mechanism of the WADA technique is fascinating.

It involves injecting a fast -acting barbiturate directly into one of the carotid arteries in the neck.

Okay.

This effectively puts only one hemisphere of the brain to sleep for a few minutes.

Just half the brain.

Just half.

By asking the patient to speak and count while half their brain is asleep, the surgeon can definitively map out which hemisphere controls language.

Oh, that's brilliant.

It ensures they don't accidentally cut into the speech centers.

Now, while removing part of the temporal lobe does cause some manageable memory deficits, it stops the seizures.

And interestingly, the text notes, it's also known to curb severe violent aggressive outbursts, which are sometimes linked directly to those abnormal electrical storms in the temporal lobe.

Yes, that connection is key.

Keep that link between brain lesions and aggression in mind, because here's where it gets really interesting.

We have to address the dark,

heavily stigmatized history of psychosurgery, specifically the prefrontal leukotomy.

Introduced by Moniz in 1936,

this operation was designed to treat serious, intractable psychiatric illnesses, primarily schizophrenia.

Right.

It was soon adapted by Freeman and Watts into what became popularly and infamously known as the frontal lobotomy.

Just imagine the sheer mechanical reality of this procedure.

Surgeons would drill burr holes on either side of the patient's skull.

They'd insert a cutting blade deep into the brain and literally sweep it back and forth in a broad arc, like a windshield wiper.

It's horrifying to picture now.

It really is.

The goal was to blindly sever a massive number of white matter connections between the higher level frontal lobe and the deep emotional subcortical circuits in the limbic system.

Later refinements, like Scoville's orbital undercutting, changed the angle of approach, but the foundational premise was exactly the same.

Still blunt force.

These were incredibly crude blunt force techniques, yet they were performed with a fervent, almost desperate enthusiasm.

It is estimated that up to 100 ,000 of these operations were performed worldwide.

100 ,000.

And it took years for the medical community to properly evaluate the devastation.

The data from the text is just grim.

It is.

A massive 1961 study by Tooth and Newton looked at over 10 ,000 cases in the UK.

What did they find?

Well, while 46 % of patients were eventually discharged from the hospital, 4 % died directly from the operation.

That's an alarmingly high mortality rate for a psychiatric treatment.

Absolutely.

And survivors were frequently left with chronic epilepsy, complete incontinence, and profound, irreversible intellectual deficits.

Today, the medical consensus is universal.

These operations were poorly founded in theory, primitive in their physical execution, and disastrously applied to thousands of unsuitable patients.

The surgery may have quieted some symptoms, but it rarely resulted in genuine clinical improvement for schizophrenia.

It's widely considered a massive scandal in the history of psychiatry.

But as you study this, you have to contextualize the era.

Put yourself in the shoes of a psychiatrist working in a crowded asylum in the early 1950s.

Right.

Before modern drugs.

Psychotropic drugs do not exist yet.

You are watching patients with severe psychosis inevitably decline into chronic, highly distressed, institutionalized states, and you are completely powerless to stop it.

They were desperate to help.

It's easy for us to judge from the future, but we have to separate the catastrophic failures of the 1950s from the highly refined psychosurgical techniques used today.

Exactly why we must look at how modern psychosurgery operates based on the text.

It is highly refined, intensely restricted, and quite rare.

There are four contemporary groups of operations detailed in the chapter.

Let's look at the mechanisms behind them.

First is stereotactic subcutate tractotomy.

Yes,

this is a vastly refined microscopic version of the old frontal lobe operations.

Using stereotactic mapping, surgeons target the white matter beneath the caudate nucleus.

But they don't use blades anymore, do they?

No blades.

They place tiny ceramic rods containing radioactive uterine 90 into the brain.

Radioactive rods.

Yes.

And the mechanism of using radioactive uterine is actually brilliant for safety.

How so?

Placing a physical blade creates unpredictable physical tearing and collateral damage.

Uterine 90 has a half -life of exactly 62 hours.

Oh, so it burns out quickly.

Very rapidly.

It creates a perfectly predictable mathematically precise lesion of exactly 25 by 15 by 5 millimeters and then becomes completely inert before the radiation can spread to adjacent speech or motor centers.

That is incredible precision.

And the clinical outcomes compared to the 1950s are night and day.

This precise lesion yields a good response in about 60 % of severely intractably depressed patients.

And it triggers a dramatic objective drop in suicide attempts.

Okay, what's the second operation?

Limbic glucotomy.

It targets the exact same subcaudate area, but it adds a secondary lesion in the cingulum bundle.

Is it for depression as well?

It's roughly as effective for depression, but it shows particular success in treating severe obsessional neurosis.

Third, we have cingulate region surgery.

A major 1980 prospective study by Corkin showed that this procedure results in absolutely no lasting neurological or behavioral deficits.

And it's incredibly effective for patients suffering from combined chronic pain and depression.

And finally, the fourth and most fiercely debated group.

Operations aimed deep at the amygdala or the posterior hypothalamus.

Yes.

This specific surgery is used for cases of severe pathological uncontrollable aggressiveness, usually in patients where there is clear medical evidence of abnormal electrical brain activity.

But we really need to pause here.

Because treating human aggression with brain surgery is incredibly controversial.

In the United States, this faced massive opposition.

Because, historically, these ideas were floated as ways to control violent criminal offenders.

Right.

Critics argue that treating human aggression surgically is treating a behavioral or social problem, not a neurological disease.

Which makes total sense.

This profound ethical and legal debate led to very strict legal controls over these procedures in the U .S.

However, looking strictly and impartially at the clinical data in the text, the operation itself appears highly effective.

What does the data show?

It reduces emotional decidability and vastly improves a patient's ability to adapt socially without causing the cognitive blunting seen in historical lobotomies.

To be clear, we are not endorsing any viewpoint here.

We are simply providing you with the scientific and clinical debate as it is presented in the chapter.

Right.

And if we connect this to the bigger picture, it really helps to realize that modern psychosurgery is always, without exception, a treatment of last resort.

It's only considered after years of every other drug and therapy failing.

Exactly.

Which prompts critics to ask a very pointed question.

If the modern surgery is so precise and effective,

why is it withheld as a last resort?

The irony is that this extreme caution is largely urged upon surgeons by the political opponents of the operations.

But the reality is that the patients undergoing these procedures are suffering profoundly.

Right.

Their quality of life is basically zero.

With untreated severe depression carrying a very real suicide risk of around 15%,

the benefits of these highly targeted interventions for selected patients can be entirely life -saving.

The era of swiveling a blade like a windshield wiper is over.

It's long gone.

The complication rates are now acceptably low, and the idea that modern psychosurgery just turns patients into emotionally deadened zombies is simply not supported by the modern clinical data.

So what does this all mean for you as you close your textbook today?

We've seen that the subcortex isn't just a passive basement holding up the tent house.

It is the roaring engine room of our consciousness, our movement, and our most primitive drives.

It's the core of everything.

And the decision to physically alter it, to sever the elevator cables or surgically silence the circuits, is one of the heaviest, yet sometimes most necessary, burdens in modern medicine.

I want to leave you with one final scientific dilemma to mull over as you study.

In modern medical science, the absolute gold standard for proving a treatment works is the double -blind placebo -controlled trial.

Right.

Where one group gets the real treatment and the other gets a fake one.

Exactly.

But think about brain surgery.

For profound ethical and methodological reasons, you cannot randomly assign a severely suicidal patient to a fake control group brain surgery just to test for the placebo effect.

Because the patient will always know their skull was open.

Exactly.

And the stakes of sham brain surgery are just far too high.

So as you continue your journey into neuropsychology, ask yourself, how can neuroscience perfectly, undeniably validate surgical treatments on the human mind when the ultimate scientific test is practically impossible to perform?

That is a fascinating question to end on.

On behalf of the Last Minute Lecture team here at The Deep Dive, thank you for listening and good luck with your studies.