Chapter 15: Emotions, Aggression & Stress

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Okay, so, I want you to try a thought experiment with me.

It's a little cinematic, so just, you know, bear with me.

Okay, I'm with you.

Imagine you're walking through, like, a really dense city park at night.

It's late.

The streetlights are flickering, casting those long, weird shadows.

It's dead quiet.

And then suddenly, from the corner of your eye, you see a shadow just lunge at you.

Okay, yeah.

Immediately, I know exactly what's happening inside your body, physiologically speaking.

Right.

It's instantaneous.

Your heart just slams against your ribs like a hammer.

Your palms get slick with cold sweat.

Stomach drops through the floor.

Your stomach drops to the floor, and every single neuron in your body is screaming, one command, survive, run, fight, you know, do something.

Right, that's the universal human baseline.

That's fear.

It's not just a feeling.

It's a biological override command.

Exactly.

Now, hold that image in your head, but this time, imagine a woman who's in that exact same park.

A man jumps out.

He's holding a knife.

He presses it to her throat.

And her heart rate, it doesn't change.

Her palms are totally dry.

She looks at the knife.

She looks at the man, and she just feels, I don't know, maybe mild curiosity.

This sounds like, I mean, it's almost like a character from a spy novel, but you're talking about a very real person, aren't you?

I am, yeah.

In the scientific literature, she's only known as Patient SM, and she isn't brave.

She isn't a Navy SEAL.

She's not suppressing her terror.

She just, she lacks the biological machinery to even process the concept of fear.

And that is exactly where we're starting today.

Welcome to the Deep Dive.

We are cracking open Chapter 15 of Behavioral Neuroscience by Brie Love and Watson.

This is a heavy one.

We aren't just talking about feelings in the poetic sense, you know, hearts breaking and spirits soaring.

We're looking at the wet wear.

The nuts and bolts.

The mechanics.

How does this lump of gray matter in our skulls generate the feeling of rage or the crushing weight of stress or the warmth of love?

And maybe more importantly for any students listening, what happens when those circuits break?

Exactly.

We've got a massive stack of research here to get through Urbac Wythe disease, the James Lange theory,

the darker side of testosterone, and even the neuroscience of why smiling might actually force you to be happy.

It's essentially the user manual for your own emotional state.

So let's go back to Patient SM, the woman who knew no fear.

This isn't a psychological condition, right?

I mean, she wasn't just raised to be tough or something.

No, no, this is purely biological.

SM suffers from a very, very rare genetic disorder called Urbac Wythe disease.

And it's incredibly specific in how it presents.

It causes calcium deposits to form in the brain.

Calcium deposits like kidney stones, but in your brain.

That's a rough way of putting it, but yeah, pretty much.

And over time, these mineral buildups essentially turned her amygdalae, both the left and the right, into stone.

They just withered away.

And because this destruction started late in her childhood, she grew up with this very specific, very localized brain damage.

The amygdala.

Okay, so that's the almond shaped thing we always hear about with threat detection.

Correct.

It's the smoke detector of the brain.

And because hers were destroyed, she completely lost that detection system.

I mean, the anecdotes in the text are just, they're wild.

You mentioned the knife incident.

Yeah, the book says she was held at knife point by a drug addict.

And she didn't just stand there.

She didn't beg for her life.

She told them, essentially, if you're going to kill me, you better go through God's angels first.

She didn't flinch.

She just kept walking.

And the attacker.

The attacker was so freaked out by her total lack of reaction that he was the one who ran away.

That's like a Jedi mind trick, but it's completely accidental.

She wasn't trying to intimidate him.

She just literally didn't register the threat.

It is accidental, but we have to be really careful here.

I think there's this tendency to view fearlessness as this ultimate stoic ideal, right?

Like a superpower.

Right.

But the text makes it very, very clear.

Fear is data.

Ah, fear is information.

Fear keeps you alive.

Exactly.

Without that data, SM is at a huge disadvantage.

The book mentions she has a really hard time navigating the world.

She has no concept of personal space.

She'll stand nose to nose with strangers because that internal alarm bell that says too close, back off, it just isn't there for her.

And she gets scammed.

Constantly.

Yeah.

She can't detect social predators.

She's outgoing.

She's friendly.

She'll chat up a waiter like he's her best friend.

But she really struggles to maintain long term friendships because she misses all the subtle cues of danger or discomfort in other people.

She's incredibly vulnerable.

It really frames the discussion perfectly.

We think of emotions as these abstract clouds floating in our minds.

But SM proves if you delete a few cubic millimeters of tissue.

The feeling just vanishes.

It grounds emotion in physics.

It tells us that feelings are physical events.

So let's define our terms because emotion is such a messy word.

If I say I feel sad, that's one thing.

But if I'm crying, that's another.

How does behavioral neuroscience even begin to categorize this?

So the textbook basically breaks it down into like three main parts.

Or pillars.

And if you take one away, it's not really a full emotion anymore.

OK, lay them out for me.

First, you have the subjective mental state.

That's the private experience.

The I feel angry thought that only you have access to.

It's your internal monologue.

OK, that's the part we usually think of as the feeling itself.

Second is the behavioral display.

This is the output.

The snarling face, the clenched fists, the slumped shoulders, the crying.

This is the communication channel to the outside world.

And the third?

The third is the physiological change.

This is the involuntary stuff, the somatic nervous system and the autonomic nervous system kicking into gear.

Heart rate, skin conductance, heavy breathing, hormone release, all that.

So feeling, acting and body.

Exactly.

And this leads to probably the biggest argument in the history of this entire field.

It's the chicken or the egg problem.

Which of those three comes first?

This is the James Lynch debate, right?

It is.

And it kind of breaks your brain a little bit if you think about it too hard.

Folks, psychology, basically common sense, says,

I see a bear.

I feel afraid.

And because I feel fear, my heart starts racing and I run.

That feels right.

The mind leads, the body follows.

I'm running because I'm scared.

But in the late 1800s, William James and Karl Lange came along and said, Nope, you've got it completely backward.

They argued that the body reacts first.

You see the bear, your body reflexively dumps adrenaline, your heart spikes, your muscles tense.

Then your conscious brain notices these physical changes and interprets them.

Wait, so the brain says, oh, my heart is racing.

I must be scared.

That's the argument.

I am afraid because I tremble.

They argued that if you could strip away the physical sensation, if you could feel your heartbeat or your stomach drop, you wouldn't actually feel fear.

You'd just have this cold intellectual understanding that there's danger.

That seems, I don't know, risky as theory.

Because doesn't a racing heart feel the same for different emotions?

I mean, if I'm about to win the lottery, my heart is pounding.

If I'm about to get into a fistfight, my heart is pounding.

You have just discovered the cannon bar theory.

Walter Cannon and Philip Bard pointed that exact thing out in the 1920s.

They said the visceral changes, the body stuff are way too slow and too generic.

It can take seconds for the heart to speed up, but we feel fear instantly.

So what was their idea?

They argued the brain decides on the emotion and triggers the body at the same time, like two parallel tracks firing off simultaneously.

So who won?

Was it James Lange or Cannon Bard?

Well, that's the thing.

It was kind of neither or maybe both.

The modern thinking throws in this third player that just changes the whole game.

And that is context.

OK, this brings us to Schachter and Singer, the cognitive twist.

This is my favorite experiment in the chapter because it's so beautifully manipulative.

It was 1962.

They took a bunch of participants and injected them with epinephrine.

Pure fight or flight juice.

Right.

Right.

So everyone's heart is racing.

Everyone's hands are shaking.

But here's the key.

They split them into two groups.

Group A was told the truth.

This injection will make your heart race and your hands shake.

OK, so they know what to expect.

Group B was told nothing or they were lied to.

So they're feeling all jittery and weird, but they don't know why.

They're physically aroused, but cognitively confused.

I see where this is going.

So then they put these people in a room with a confederate, an actor working for the scientists.

In one scenario, the actor is acting absolutely furious, stomping around, complaining about the questionnaire, be a total jerk.

And in the other scenario, the actor is euphoric.

He's playing with hula hoops, throwing paper airplanes, just having the best day of his life.

So what happened to the people who got the adrenaline shot?

OK, so the people who were warned group A, they felt no real emotion.

They just ignored the actor.

They said, my heart is pounding because of that shot I got.

They had a cognitive label for their physical state.

They had an explanation, so it didn't bother them.

But the people who are not warned,

their brains panicked.

They had all this raw physical energy and no explanation for it.

So they looked to the actor in the room to figure out what they were supposed to be feeling.

No way.

Yes.

If they were in the room with the angry guy, they reported feeling furious themselves.

If they were with a happy guy, they reported feeling overjoyed.

That is wild.

So the emotion wasn't the adrenaline.

The adrenaline was just the volume knob.

That's a great way to put it.

The emotion was the story the brain invented to explain why the volume was so loud.

Context is king.

This is the cognitive attribution model.

It implies that our emotions are essentially our brain's best guess about what our body is doing based on who we're with and what's happening around us.

Which makes you wonder about things like mob mentality.

You're in a crowd, everyone is shouting, your heart rate is up, and your brain just decides, OK, I guess we are angry now.

Precisely.

It explains why a political rally or a sporting event can swing so wildly between pure joy and pure aggression.

The physiological arousal is identical, only the narrative changes.

Speaking of physiological arousal, this seems like the perfect segue to the so -called lie detector.

Because that's all a polygraph is, isn't it?

It's just an arousal meter.

We really need to stop calling them lie detectors.

The text is pretty brutal on this.

It clarifies the terminology.

It's a polygraph.

Poly meaning many, graph meaning right.

It just records blood pressure, respiration, and skin conductance, which is basically how much you're sweating.

And the theory is that lying is hard work.

It makes you nervous.

So you sweat more.

That is the flawed assumption, yes.

But based on what we just talked about with Schachter and Singer, what else makes you sweat?

Fear, anxiety, anger,

confusion, being accused of a crime I didn't commit.

Exactly.

Fear, anxiety, and anger all share incredibly similar physiological profiles.

So if I'm an innocent person and you hook me up to a machine and ask, did you kill your wife?

I'm going to have a massive physiological spike just from the stress of the question itself.

And the machine is going to flag that as a lie.

The text points out that anxious innocents can and do fail these tests all the time.

And it must work the other way, too.

You can hack it.

Oh, you can.

There's the classic example of Aldrich Ames.

He was a CIA counterintelligence officer who was actually a mole for the Soviet Union.

A double agent.

Yeah.

He compromised countless operations and he took the polygraph twice while he was a spy.

And passed.

With flying colors.

His Soviet handlers told him essentially, just relax.

It's just a machine.

Make small talk with the operator to establish a really calm baseline.

And because he was a cold, calculated operator, or maybe just because he was so confident, he didn't have that telltale physiological spike.

So the machine measures excitement, not truth.

Exactly.

The text mentions there's some push now toward fMRI lie detection, looking at the prefrontal cortex to see if the brain is working harder to invent a lie.

But even that is filled with problems.

For now, there is no Pinocchio's nose in the brain.

Let's pivot from the internal mechanics to the external, the face.

We can't talk about the biology of emotion without bringing Charles Darwin into the room.

Darwin is the grandfather of this whole field.

He wrote the expression of the emotions in man and animals.

And he made a really bold claim for his time.

That facial expressions aren't cultural.

They aren't something we learn like a language.

They're biological hardware.

He was looking at primates for this, right?

He was.

He noticed that non -human primates use the same facial muscles we do in very similar contexts.

A grimace.

That's fear or submission.

A tense, open mouth.

That's a threat or anger.

And the play face.

The play face is the best one.

Chimps open their mouths when they play wrestle.

Darwin argued that this is the evolutionary ancestor of human laughter.

The text mentions something here that I just absolutely loved.

Rat laughter.

Yes.

This is from the work of Jack Panksepp.

You can't hear it with the naked ear.

But if you use a bat detector, an ultrasonic microphone, and you tickle a rat.

Wait, you just, you tickle the rat with your finger.

You tickle the rat.

And it emits these high frequency 50 kilohertz chirps.

And the rat will actually chase your hand to get tickled more.

It suggests that joy and play are ancient, ancient circuits.

We share a laugh with rodents.

That is so charming.

But okay, let's challenge that universal idea a bit.

If I smile in New York City and I smile in a remote tribal village in Papua New Guinea, does it really mean the exact same thing?

For the most part, yes.

Paul Ekman is the big name here.

He identified what he calls eight universal expressions.

Anger, sadness, happiness, fear,

disgust, surprise, contempt, and embarrassment.

He went to these isolated, non -literate cultures and found that yes, they recognize a smile as happiness and a scowl as anger.

But the text does add a little caveat.

It does.

There was some confusion between surprise and disgust in some of the isolated groups.

And really, if you think about it, that makes sense.

Both involve a sudden reaction to something unexpected, a scrunching of the face.

So while the hardware seems to be universal, culture acts as a bit of a filter on how we interpret the more subtle nuances.

Now here's the part that just blows my mind.

We know feelings control the face.

But does the face control the feelings?

The facial feedback hypothesis.

This goes right back to the James Lange idea.

If I force my face into a smile, can I actually trick my brain into being happy?

Tell me about the pencil study.

This is a classic.

They had participants hold a pencil in their mouth.

One group held it with their teeth.

You can try this right now.

If you hold a pencil in your teeth, not letting it touch your lips,

it forces your zygomatic muscles to contract.

It physically forces a smile.

Okay, I'm doing it.

I look absolutely ridiculous.

You do.

Now the other group held the pencil between their nose and upper lip.

And to keep it there, you have to pout.

It forces a frown.

And then they just showed them cartoons.

Yep.

And the people with the forced smiles rated the cartoons as significantly funnier than the people who were forced to frown.

That is incredible.

So the sensory data coming back from my cheek muscles is actually telling my brain, hey, we're smiling, so this thing must be funny.

It's a feedback loop.

And there's a really modern application of this that's kind of disturbing.

Botox.

Oh, right, because you're paralyzing the muscles you'd use to frown.

Exactly.

If you get Botox in your forehead to stop frowning, you literally cannot make a fearful or angry face as effectively.

And people who do this consistently report that they feel those emotions less intensely.

That's astonishing.

By smoothing out the wrinkles, you're kind of smoothing out your soul.

In a way.

It suggests that our emotional depth is basically tied to our physical ability to express it.

So we're born with this hardware, but are the settings already dialed in?

The text talks about something called individual response stereotypy.

This is the nature side of the nature versus nurture debate.

Researchers tracked individuals from infancy all the way to adulthood.

They started with newborns and did a really simple test.

They just swabbed some rubbing alcohol on the baby's skin.

Cold sensation, sharp smell, a mild shock to the system.

Exactly.

And they watched the reaction.

Some babies, about 20 % of them, went absolutely ballistic, crying, thrashing, massive heart rate spike.

They called these the high reactives and the low reactives.

They barely even noticed.

Now, here's the kicker.

They followed these kids for years and years, and the high reactive babies grew up to be shy, anxious, risk averse adults.

So if you're a jumpy baby, you're likely to be an anxious adult.

Generally, yes.

They even put the adults in fMRI scanners later on.

The people who were high reactive babies had amygdalae that lit up like fireworks when they were shown pictures of strangers.

It's like they're wired for high alert threat detection from day one.

That's somewhat deterministic.

It implies some people are just born to worry.

But let's actually map this stuff out in the brain.

We keep talking about the amygdala, but that's not the only player in the game.

How did we find the pleasure center?

Totally by accident, which is how a lot of this stuff happens.

In 1954, Olds and Milner were trying to study the reticular formation in rats.

They missed.

They implanted the electrode in the septum instead.

And they gave the rats a button to press to stimulate that area.

Yes, and the rats.

Well, they became addicts.

They would press that lever thousands of times an hour.

They would ignore food.

They would ignore water.

Nursing mothers would actually ignore their pups just to keep pressing that lever.

They were hacking their own reward system.

They had tapped directly into the medial forebrain bundle.

This is the dopamine superhighway that runs from the midbrain up to the nucleus accumbens.

This is the exact same pathway that cocaine,

heroin, and meth all hijack.

It's the circuitry of wanting.

So that's pleasure.

What about rage?

The text mentions something called decorticate rage.

This is a bit gruesome, but it's very illustrative.

Early researchers removed the entire cerebral cortex from dogs.

That's the wrinkly outer layer, the thinking part of the brain.

What was left?

Just the primitive subcortical structures.

And the result was terrifying.

The dogs would fly into a rage at the slightest touch.

They would snap, bite, and snarl at nothing at all.

They called it cham rage because it wasn't directed at anything specific.

It implies that the rage is sort of always there, just waiting.

Exactly.

The rage impulse comes from the deep brain, the hypothalamus specifically.

The cortex's job is to put the brakes on to say, whoa, don't bite that.

That's just the wind.

Without the cortex, the brakes are completely cut.

And this brings us to the limbic system.

The emotional circle, yeah.

James Papez and later Paul McLean mapped this out.

It's this loop connecting the hippocampus for memory, the cingulate cortex for error detection, the fornix, and of course, the amygdala for fear.

And when you damage this whole loop, you can get Kluber -Boosey syndrome.

This was the study they did on monkeys, right?

With bilateral temporal lobe damage.

Yes.

The monkeys became incredibly tame.

They lost all fear of snakes and humans.

But they also became hypersexual.

And this is the weirdest part.

They developed what they called oral tendencies.

They put everything in their mouth.

Everything.

Rocks, sticks, their own feces.

Because the part of the brain that tags objects as good, bad, food or danger was just gone.

They'd physically taste everything to try and relearn what it was.

It's a total reset of their entire value system.

It is.

It really shows that the limbic system provides the emotional color to our visual world.

Without it, everything is just neutral.

OK, let's double -click on the amygdala for a minute.

The book calls it the Anatomy of Fear.

We know it's the hub.

But how does it get the information?

The text talks about the two roads.

This is Joseph Ledoux's work, and it's absolutely crucial for understanding things like anxiety.

Let's say you're hiking.

You look down and see a coiled shape on the path.

Snake?

That visual information hits your thalamus, the brain's main relay station.

From there, it splits.

Path one is the low road.

It goes directly from the thalamus to the amygdala.

No processing, no thinking.

So speed is the priority?

Milliseconds.

The amygdala screams,

freeze, or jumpy.

And you're in the air before your conscious brain even knows why.

It's a pure survival reflex.

Then the high road?

The high road is slower.

That signal goes from the thalamus up to the sensory cortex and then to the hippocampus.

It analyzes the shape.

It checks your memory banks.

And it realizes, oh, this is the garden hose.

And then it sends a signal down to the amygdala to say, stand down, false alarm.

Exactly.

And this is the core mechanism of phobias in PTSD.

Either the low road is way too loud or the high road is too quiet.

You jump at the garden hose and you just can't calm down.

The book also mentions extinction,

unlearning fear.

So if you learn that a tone predicts a shock, how do you unlearn it?

The prefrontal cortex has to actively inhibit the amygdala.

And interestingly, the text mentions cannabinoids here.

Mice that are missing their natural cannabinoid receptors have a really hard time forgetting fear.

So our body's own endogenous marijuana system helps us let go of bad memories.

It really seems so.

And it has huge implications for treating things like PTSD.

But let's loop all the way back to patient SM.

We said she has no amygdala, no low road, no high road for fear.

She laughs at haunted houses.

She thinks spiders are cute.

But the researchers found the one thing they could finally break her.

The twist.

They asked her to inhale air that was mixed with 35 percent carbon dioxide.

That's not toxic, but it makes you feel like you can't breathe, right?

It triggers what's called air hunger,

a primal suffocation response.

And SM, she panicked for the first time in decades.

She screamed.

She flailed her arms.

She was terrified.

Wow.

Her fear center is gone.

It turns out the amygdala monitors the outside world for threats.

Snakes, knives, bad guys.

But internal threats, your body's pH balance, oxygen levels, pain.

Those are monitored by the brain stem, an even deeper, more primitive system.

So she can fear death, but only if the threat comes from the inside out.

Exactly.

It shows that fear isn't just one thing.

It's a layered complex system.

Let's switch gears a little bit.

We've done a lot of fear and rage.

What about love?

Is there a love spot in the brain?

Not a single spot, no, but definitely a network.

Bartels and Zeke put people in fMRI scanners and showed them pictures of their romantic partners and then just pictures of their friends for comparison.

What lit up for the romantic partners?

The insula and the anterior cingulate.

But the most interesting part is what went dark.

When people were looking at a photo of their lover, their amygdala and their right prefrontal cortex deactivated.

The fear center and the judgment center.

Exactly.

Love is blind is a literal neurobiological reality.

When you are deep in love, the parts of your brain that criticize and assess danger

effectively just they shut down.

You literally cannot see the flaws in the same way.

That is both beautiful and incredibly dangerous.

What about a less pleasant emotion?

Envy.

Envy is brutal.

It activates the anterior cingulate cortex, the exact same area that lights up when you're in physical pain.

So jealousy literally hurts.

It does.

And it's evil twin Schadenfreude, you know, taking joy in the suffering of others.

That lights up the nucleus accumbens, the reward center.

So if I see my rival fail, my brain gives me a little hit of dopamine.

We are petty biological machines.

Yes.

Let's talk about aggression.

Testosterone, the so -called male hormone.

We always assume more testosterone equals more violence.

And in animals, that's largely true.

You castrate a male mouse.

He stops fighting.

You give him T shots.

He starts fighting again.

But in humans, it is much, much more nuanced.

It's about status, isn't it?

Yes.

Testosterone doesn't just make you aggressive.

It drives you to achieve and maintain social dominance.

The text mentions the winter effect in wrestling and chess.

Right.

If you win a chess match, no physical violence involved at all.

Your testosterone spikes.

If you lose, it drops.

It's basically regulating your confidence to take on the next challenge.

And this even applies to sports fans.

It does.

If your team wins the World Cup, the testosterone levels in the fan days go up.

If they get crushed, the levels crash.

You're biologically synced to the dominance of your chosen tribe.

That explains a lot about the behavior of soccer hooligans.

But what about the actual brain switches?

The text mentions the VMH again, the ventromedial hypothalamus and a really incredible study using optogenetics, where they can turn specific neurons on and off with a laser light.

They basically found the murder switch in mice.

That sounds ominous.

It is.

They turn the light on and the mouse immediately attacks anything.

A male, a female, an inanimate object, it just bites and kills.

They turn the light off and the mouse stops instantly.

It shows that aggression is a specific hardwired program that can be flipped on or off.

And in humans who are hyper aggressive psychopaths, for instance, what's different in their brains?

Psychopaths are fascinating biologically.

We tend to think of them as these criminal masterminds, but really they have brakes that just don't work.

Their prefrontal cortex, the inhibition center, is often smaller and less active than a typical brain.

So they have the impulse, but they don't have that little voice saying, don't do that.

Exactly.

Plus, they lack the physiological arousal we talked about at the very beginning.

They don't have that empathetic stress response.

If I show you a picture of a crying child, you feel a pang of distress.

A psychopath feels nothing.

They are physically detached from the emotional weight of their actions.

Which brings us to the final major topic of the chapter, stress.

The silent killer.

We use the word stress for everything, but the book makes a clear distinction between the two systems involved.

The fast one and the slow one.

Exactly.

The fast system is the sympathetic nervous system.

This is the adrenal medulla dumping epinephrine adrenaline.

This is the jump response.

It's over in minutes.

And the slow system.

That's the HPA axis, hypothalamus pituitary adrenal cortex.

This releases the hormone cortisol and cortisol is for the long haul.

It mobilizes your glucose stores so you can survive a famine or a long arduous trek.

But we aren't trekking across the savanna.

We're worrying about emails.

And that is the fundamental problem of modern life.

Our bodies treat a stressful inbox like a physical predator.

The text details this amazing study on parachute jumpers.

A pretty high stress environment.

The ultimate.

On their first day, their cortisol and epinephrine were just off the charts.

They were terrified.

But as they kept jumping day after day, the stress hormones dropped.

They habituated to the experience.

But their testosterone did something weird, right?

Yeah.

On the later jumps, their testosterone spiked before they jumped.

Their body shifted from a state of I am going to die to I am the master of the sky.

They chemically transitioned from being the victim of a situation to being its conqueror.

But not everyone adapts like that.

Why do some people crumble under stress while others seem to get stronger?

This is the stress immunization concept.

This is, for me, the most profound part of the entire chapter.

They were looking at rat pups and they found that pups who were handled by humans, which is a mild stressor for them, grew up to be more resilient adults.

So what doesn't kill you makes you stronger.

That's what they thought.

But they were wrong.

It wasn't the stress.

It was what happened after the stress.

When the researchers put the pups back in the cage, their mothers would lick and groom them intensely to comfort them.

So it was the comfort that mattered, not the stress.

Yes.

Pups that were stressed but not comforted by their mothers didn't get the benefit.

In fact, they grew up to be more anxious.

And this actually changes their DNA.

It changes the expression of the DNA.

This is epigenetics.

The mother's tongue, the physical act of grooming released chemicals in the pups brain that removed these silencer markers from their DNA.

It permanently turned up the volume on their stress regulation genes.

So the mother's love literally recoded the baby's brain software for life.

That's a perfect way to put it.

And the text draws a very dark parallel to humans.

They examined the brains of suicide victims who had documented histories of childhood abuse.

They found the same epigenetic markers as the neglected rats.

Their brains had been chemically locked into a state of high stress vulnerability.

The environment of their childhood was physically written into their biology.

That is, that's incredibly heavy.

But it explains so much about public health.

It leads right into the final topic.

Psychoneuroimmunology, the link between the mind and the immune system, leads to think they were totally separate.

But stress, specifically cortisol, actively suppresses the immune system.

Which is why you always get sick after finals week.

Precisely.

Or why type A personalities were thought to get heart attacks.

Though the text corrects that common misconception.

It's not type A.

It's not being hardworking or ambitious.

Hostility.

Yes.

The data points to one specific trait.

Being angry, mistrustful and cynical is the real killer.

If you view the world as a constant battle, your body stays in a constant state of inflammation and high blood pressure.

And on the flip side, having a sense of turpice actually protects you.

It does.

If you feel your life has meaning, you are statistically less likely to die from heart disease, even after you've been diagnosed.

Your mindset acts as a genuine shield for your heart.

So let's zoom out.

We have covered a lot of ground here, from a woman with the stone amygdala who fights off knife wielders, to the rats that laugh when you tickle them, to the epigenetic programming of our stress responses by our mothers.

It's a dense landscape.

But I think the main takeaway is crystal clear.

Emotions are not just ghosts in the machine.

They are the machine.

Every single feeling you have, the terror, the love, the petty envy when your rival fails, it's a firing pattern.

It's a chemical release, a biological event that has been honed by millions of years of evolution.

We are walking, talking, feeling biological algorithms.

And that leads me to my final thought for you listening today.

We now know that forcing a smile can trick your brain into feeling happiness.

We know that a mother's touch can literally rewrite a child's gene expression.

We know that your sense of purpose can keep your heart beating.

The line gets very, very blurry.

Exactly.

So if the mind can physically alter the structure and function of the body and the body's physical state dictates the mind, where do you actually begin?

Are you the architect of your own biology or are you just its passenger?

That's the question that keeps neuroscientists awake at night.

Thank you for taking this deep dive with us.

It's been a real pleasure exploring Chapter 15 of behavioral neuroscience with you all.

A big thank you from the last minute lecture team.

Stay curious and try to stay calm.

We'll catch you on the next one.