Behave - The Biology of Humans at Our Best and Worst by Robert M. Sapolsky

a beta-ranking male baboon loses a fight to the alpha, and he chases the omega male;

giving ulcers can help you avoid getting them.

“Sometimes I’ll stop sooner than I planned, but not because it hurts; it’s not something I notice. It’s as an act of kindness to my knees.”

Layer 1: An ancient part of the brain, at its base, found in species from humans to geckos. This layer mediates automatic, regulatory functions. If body temperature drops, this brain region senses it and commands muscles to shiver. If blood glucose levels plummet, that’s sensed here, generating hunger. If an injury occurs, a different loop initiates a stress response.

Layer 2: A more recently evolved region that has expanded in mammals. MacLean conceptualized this layer as being about emotions, somewhat of a mammalian invention. If you see something gruesome and terrifying, this layer sends commands down to ancient layer 1, making you shiver with emotion. If you’re feeling sadly unloved, regions here prompt layer 1 to generate a craving for comfort food. If you’re a rodent and smell a cat, neurons here cause layer 1 to initiate a stress response.

Layer 3: The recently evolved layer of neocortex sitting on the upper surface of the brain. Proportionately, primates devote more of their brain to this layer than do other species. Cognition, memory storage, sensory processing, abstractions, philosophy, navel contemplation. Read a scary passage of a book, and layer 3 signals layer 2 to make you feel frightened, prompting layer 1 to initiate shivering. See an ad for Oreos and feel a craving—layer 3 influences layers 2 and 1. Contemplate the fact that loved ones won’t live forever, or kids in refugee camps, or how the Na’vis’ home tree was destroyed by those jerk humans in Avatar (despite the fact that, wait, Na’vi aren’t real!), and layer 3 pulls layers 2 and 1 into the picture, and you feel sad and have the same sort of stress response that you’d have if you were fleeing a lion.

The hypothalamus, a limbic structure, is the interface between layers 1 and 2, between core regulatory and emotional parts of the brain.

Consistent with that, the hypothalamus gets massive inputs from limbic layer 2 structures but disproportionately sends projections to layer 1 regions. These are the evolutionarily ancient midbrain and brain stem, which regulate automatic reactions throughout the body.

The sympathetic nervous system (SNS) mediates the body’s response to arousing circumstances, for example, producing the famed “fight or flight” stress response. To use the feeble joke told to first-year medical students, the SNS mediates the “four Fs—fear, fight, flight, and sex.”

Meanwhile, the parasympathetic nervous system (PNS) arises from different midbrain/brain-stem nuclei that project down the spine to the body. In contrast to the SNS and the four Fs, the PNS is about calm, vegetative states. The SNS speeds up the heart; the PNS slows it down. The PNS promotes digestion; the SNS inhibits it (which makes sense—if you’re running for your life, avoiding being someone’s lunch, don’t waste energy digesting breakfast).

The cortex is the gleaming, logical, analytical crown jewel of layer 3. Most sensory information flows there to be decoded. It’s where muscles are commanded to move, where language is comprehended and produced, where memories are stored, where spatial and mathematical skills reside, where executive decisions are made.

The greatest lateralization occurs in the cortex; the left hemisphere is analytical, the right more involved in intuition and creativity.

The amygdala/aggression link pops up in two notorious cases of violence. The first concerns Ulrike Meinhof, a founder in 1968 of the Red Army Faction (aka the Baader-Meinhof Gang), a terrorist group responsible for bombings and bank robberies in West Germany. Meinhof had a conventional earlier life as a journalist before becoming violently radicalized. During her 1976 murder trial, she was found hanged in her jail cell (suicide or murder? still unclear). In 1962 Meinhof had had a benign brain tumor surgically removed; the 1976 autopsy showed that remnants of the tumor and surgical scar tissue impinged on her amygdala.7 A second case concerns Charles Whitman, the 1966 “Texas Tower” sniper who, after killing his wife and mother, opened fire atop a tower at the University of Texas in Austin, killing sixteen and wounding thirty-two,

He left notes by the bodies of his wife and his mother, proclaiming love and puzzlement at his actions: “I cannot rationaly [sic] pinpoint any specific reason for [killing her],” and “let there be no doubt in your mind that I loved this woman with all my heart.” His suicide note requested an autopsy of his brain, and that any money he had be given to a mental health foundation. The autopsy proved his intuition correct—Whitman had a glioblastoma tumor pressing on his amygdala.

fear activates the amygdala in humans, with more activation predicting more behavioral signs of fear.

Research shows that rejecting an offer is an emotional decision, triggered by anger at a lousy offer and the desire to punish.

Tags: #emotion #anger

Instead, these findings suggest that the amygdala injects implicit distrust and vigilance into social decision making.23 All thanks to learning. In the words of the authors of the study, “The generosity in the trust game of our BLA-damaged subjects might be considered pathological altruism, in the sense that inborn altruistic behaviors have not, due to BLA damage, been un-learned through negative social experience.” In other words, the default state is to trust, and what the amygdala does is learn vigilance and distrust.

the opposite of love is not hate, it’s indifference.

What does the frontal cortex do? Its list of expertise includes working memory, executive function (organizing knowledge strategically, and then initiating an action based on an executive decision), gratification postponement, long-term planning, regulation of emotions, and reining in impulsivity.

the frontal cortex makes you do the harder thing when it’s the right thing to do.

The frontal cortex is the last brain region to fully mature, with the most evolutionarily recent subparts the very last. Amazingly, it’s not fully online until people are in their midtwenties.

Importantly, increase cognitive load on the frontal cortex, and afterward subjects become less prosocial*—less charitable or helpful, more likely to lie.

During REM sleep, when dreaming occurs, the frontal cortex goes off-line, and dream scriptwriters run wild. Moreover, if the frontal cortex is stimulated while people are dreaming, the dreams become less dreamlike, with more self-awareness.

The functions of the cognitive dlPFC are the essence of doing the harder thing.56 It’s the most active frontocortical region when someone forgoes an immediate reward for a bigger one later. Consider a classic moral quandary—is it okay to kill one innocent person to save five? When people ponder the question, greater dlPFC activation predicts a greater likelihood of answering yes (but as we’ll see in chapter 13, it also depends on how you ask the question).

In one version you pull a lever, diverting the trolley onto a side track. This saves the five, but the trolley kills someone who happened to be on this other track; 70 to 90 percent of people say they would do this. In the second scenario you push the person in front of the trolley with your own hands. This stops the trolley, but the person is killed; 70 to 90 percent say no way. The same numerical trade-off, but utterly different decisions.

As with much about the frontal cortex, it’s context, context, context.

Reward, pleasure, and happiness are complex, and the motivated pursuit of them occurs in at least a rudimentary form in many species. The neurotransmitter dopamine is central to understanding this.

Food evokes dopamine release in hungry individuals of all species, with an added twist in humans. Show a picture of a milkshake to someone after they’ve consumed one, and there’s rarely dopaminergic activation—there’s satiation.

In one study a subject would play an economic game with someone, where a player is rewarded under two circumstances: (a) if both players cooperate, each receives a moderate reward, and (b) stabbing the other person in the back gets the subject a big reward, while the other person gets nothing. While both outcomes increased dopaminergic activity, the bigger increase occurred after cooperation.*

for a medieval peasant, this must have been the loudest human-made sound they ever experienced, awe-inspiring in now-unimaginable ways. No wonder they signed up for the religion being proffered. And now we are constantly pummeled with sounds that dwarf quaint organs. Once, hunter-gatherers might chance upon honey from a beehive and thus briefly satisfy a hardwired food craving. And now we have hundreds of carefully designed commercial foods that supply a burst of sensation unmatched by some lowly natural food. Once, we had lives that, amid considerable privation, also offered numerous subtle, hard-won pleasures. And now we have drugs that cause spasms of pleasure and dopamine release a thousandfold higher than anything stimulated in our old drug-free world.

But our frequent human tragedy is that the more we consume, the hungrier we get. More and faster and stronger. What was an unexpected pleasure yesterday is what we feel entitled to today, and what won’t be enough tomorrow.

If you know your appetite will be sated, pleasure is more about the appetite than about the sating.

the hub of fear, aggression, and arousal centered in the amygdala; the hub of reward, anticipation, and motivation of the dopaminergic system; and the hub of frontal cortical regulation and restraint of behavior.

Often we’re clueless about this because animals can sense things in ranges that we can’t, or with sensory modalities we didn’t know exist.

By one hundred milliseconds, brain function already differs in two depressing ways, depending on the race of the face (as shown with neuroimaging). First, in a widely replicated finding, the amygdala activates. Moreover, the more racist someone is in an implicit test of race bias (stay tuned), the more activation there is.8

Viewing a black individual evokes less of an N200 waveform than does seeing someone white. The greater the P200/N200 ratio (i.e., the greater the ratio of I’m-feeling-threatened to Hold-on-a-sec), the greater the likelihood of shooting an unarmed black individual.

There’s also subliminal cuing about beauty.18 From an early age, in both sexes and across cultures, attractive people are judged to be smarter, kinder, and more honest. We’re more likely to vote for attractive people or hire them, less likely to convict them of crimes, and, if they are convicted, more likely to dole out shorter sentences.

The shape of women’s faces changes subtly during their ovulatory cycle, and men prefer female faces at the time of ovulation.

However, sniffing terrified sweat (but not contented sweat) caused amygdaloid activation, a bigger startle response, improved detection of subliminal angry faces, and increased odds of interpreting an ambiguous face as looking fearful. If people around you smell scared, your brain tilts toward concluding that you are too.

As a repeating theme, pain does not cause aggression; it amplifies preexisting tendencies toward aggression. In other words, pain makes aggressive people more aggressive, while doing the opposite to unaggressive individuals.

Various studies, predominantly by Roy Baumeister of Florida State University, show that when the frontal cortex labors hard on some cognitive task, immediately afterward individuals are more aggressive and less empathic, charitable, and honest.

The mythic elements of the Genovese case prompt the quasi myth that in an emergency requiring brave intervention, the more people present, the less likely anyone is to help—“There’s lots of people here; someone else will step forward.”

testosterone is far less relevant to aggression than usually assumed.

But testosterone makes people overconfident and overly optimistic, with bad consequences. In one study, pairs of subjects could consult each other before making individual choices in a task. Testosterone made subjects more likely to think their opinion was correct and to ignore input from their partner. Testosterone makes people cocky, egocentric, and narcissistic.

Testosterone boosts impulsivity and risk taking, making people do the easier thing when it’s the dumb-ass thing to do.7 Testosterone does this by decreasing activity in the prefrontal cortex and its functional coupling to the amygdala and increasing amygdaloid coupling with the thalamus—the source of that shortcut path of sensory information into the amygdala. Thus, more influence by split-second, low-accuracy inputs and less by the let’s-stop-and-think-about-this frontal cortex.

rising testosterone levels increase aggression only at the time of a challenge.

Remarkably, watching your favorite team win raises testosterone levels, showing that the rise is less about muscle activity than about the psychology of dominance, identification, and self-esteem.

Testosterone levels rise, reaching the brain. If this occurs because someone is challenging you, you head in the direction of aggression.

The challenge hypothesis has a second part to it. When testosterone rises after a challenge, it doesn’t prompt aggression. Instead it prompts whatever behaviors are needed to maintain status. This changes things enormously.