Behave: The Biology of Humans at Our Best and Worst - Robert M. Sapolsky  ## Metadata - Author: **Robert M. Sapolsky** - Full Title: Behave: The Biology of Humans at Our Best and Worst - Category: #books ## Highlights - What occurred in the prior seconds to minutes that triggered the nervous system to produce that behavior? This is the world of sensory stimuli, much of it sensed unconsciously. ([View Highlight](https://read.readwise.io/read/01j3dtcgzgx56c5m6dsedpx9pb)) - We start by considering the brain’s macroorganization, using a model proposed in the 1960s by the neuroscientist Paul MacLean.[1](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber16) His “triune brain” model conceptualizes the brain as having three functional domains ([View Highlight](https://read.readwise.io/read/01j3dvqwq3adfk8sq6vevcvyef)) - 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. ([View Highlight](https://read.readwise.io/read/01j3dvr3qvmx58pesx6sfbv048)) - 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. ([View Highlight](https://read.readwise.io/read/01j3dvr9pd9b4szt558ftztp6h)) - 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. ([View Highlight](https://read.readwise.io/read/01j3dvrrvcm9eenb8r0aqhqhev)) ## New highlights added July 23, 2024 at 7:49 AM - But if you asked amygdala experts what behavior their favorite brain structure brings to mind, “aggression” wouldn’t top their list. It would be fear and anxiety.[9](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber24) Crucially, the brain region most involved in feeling afraid and anxious is most involved in generating aggression. ([View Highlight](https://read.readwise.io/read/01j3dwy5ncvcbq5mwqd65awvar)) - Powerful support for an amygdaloid role in fear processing comes from post-traumatic stress disorder (PTSD). In PTSD sufferers the amygdala is overreactive to mildly fearful stimuli and is slow in calming down after being activated.[13](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber28) Moreover, the amygdala expands in size with long-term PTSD. ([View Highlight](https://read.readwise.io/read/01j3dx1qjjs5y9e2dvjrede1kw)) - The amygdala/hippocampus interface. Naturally, the amygdala talks to other limbic structures, including the hippocampus. As reviewed, typically the amygdala learns fear and the hippocampus learns detached, dispassionate facts. ([View Highlight](https://read.readwise.io/read/01j3exyafys8tdcg8admw79mdy)) - Motor outputs. There’s a second shortcut regarding the amygdala, specifically when it’s talking to motor neurons that command movement.[30](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber45) Logically, when the amygdala wants to mobilize a behavior—say, fleeing—it talks to the frontal cortex, seeking its executive approval. But if sufficiently aroused, the amygdala talks directly to subcortical, reflexive motor pathways. ([View Highlight](https://read.readwise.io/read/01j3exxn4qcwqyrtbsryz0zcd3)) - Arousal. Ultimately, amygdala outputs are mostly about setting off alarms throughout the brain and body. ([View Highlight](https://read.readwise.io/read/01j3exwyaq7615p76peqt3wjbd)) - Among humans, the larger someone’s social network (measured by number of different people texted), the larger a particular PFC subregion (stay tuned). ([View Highlight](https://read.readwise.io/read/01j3eywcb2de9q1v0basnwf5v7)) - And there’s another nonpathological circumstance where the PFC silences, producing emotional tsunamis: during orgasm. ([View Highlight](https://read.readwise.io/read/01j3ez4kp8mjg71cd4mwm3ne2w)) - The functions of the cognitive dlPFC are the essence of doing the harder thing.[56](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber71) It’s the most active frontocortical region when someone forgoes an immediate reward for a bigger one later. ([View Highlight](https://read.readwise.io/read/01j3ez7q2rjzyzgwkw27ekx3yc)) ## New highlights added July 23, 2024 at 1:26 PM - We do something even beyond this unprecedented gratification delay: we use the dopaminergic power of the happiness of pursuit to motivate us to work for rewards that come *after we are dead*—depending on your culture, this can be knowing that your nation is closer to winning a war because you’ve sacrificed yourself in battle, that your kids will inherit money because of your financial sacrifices, or that you will spend eternity in paradise. It is extraordinary neural circuitry that bucks temporal discounting enough to allow (some of) us to care about the temperature of the planet that our great-grandchildren will inherit. Basically, it’s unknown how we humans do this. We may merely be a type of animal, mammal, primate, and ape, but we’re a profoundly unique one. ([View Highlight](https://read.readwise.io/read/01j3fk2gta0t9djqhnc96fhm2f)) ## New highlights added July 23, 2024 at 9:21 PM - Starting with a 1979 study, low levels of serotonin in the brain were shown to be associated with elevated levels of human aggression, with end points ranging from psychological measures of hostility to overt violence. ([View Highlight](https://read.readwise.io/read/01j3gfax7stbawad2cj9bwqj6t)) ## New highlights added July 25, 2024 at 8:13 AM - The shape of women’s faces changes subtly during their ovulatory cycle, and men prefer female faces at the time of ovulation. ([View Highlight](https://read.readwise.io/read/01j3k3vcm4yjzj6senjmwt42wd)) - Back to amygdaloid activation in whites subliminally viewing black faces. Chad Forbes of the University of Delaware shows that the amygdala activation increases if loud rap music—a genre typically associated more with African Americans than with whites—plays in the background. The opposite occurs when evoking negative white stereotypes with death metal music blaring. ([View Highlight](https://read.readwise.io/read/01j3k41wj0e7wfm786jew5gq05)) - As noted, rodent pheromones carry information about sex, age, reproductive status, health, and genetic makeup, and they alter physiology and behavior. ([View Highlight](https://read.readwise.io/read/01j3k49hry4b41bppnhg43704b)) - women preferring the smell of high-testosterone men. ([View Highlight](https://read.readwise.io/read/01j3k4a6czmaxdcvj0nmkg2yhq)) - How do your feelings and your body’s automatic (i.e., “autonomic”) function interact? It seems obvious—a lion chases you, you feel terrified, and thus your heart speeds up. James and Lange suggested the opposite: you subliminally note the lion, speeding up your heart; then your conscious brain gets this interoceptive information, concluding, “Wow, my heart is racing; I must be terrified.” In other words, you decide what you feel based on signals from your body. ([View Highlight](https://read.readwise.io/read/01j3k4z1edq2g9wd7p2he101t9)) - There’s support for the idea—three of my favorites are that (a) forcing depressed people to smile makes them feel better; (b) instructing people to take on a more “dominant” posture makes them feel more so (lowers stress hormone levels); and (c) muscle relaxants decrease anxiety (“Things are still awful, but if my muscles are so relaxed that I’m dribbling out of this chair, things must be improving”). ([View Highlight](https://read.readwise.io/read/01j3k50qmj6vxc5dzbfeb7tx3r)) - One of my favorite examples concerns the Prisoner’s Dilemma, the economic game where participants decide whether to cooperate or compete at various junctures.[29](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber156) And behavior is altered by “situational labels”—call the game the “Wall Street Game,” and people become less cooperative. Calling it the “Community Game” does the opposite. Similarly, have subjects read seemingly random word lists before playing. Embedding warm fuzzy prosocial words in the list—“help,” “harmony,” “fair,” “mutual”—fosters cooperation, while words like “rank,” “power,” “fierce,” and “inconsiderate” foster the opposite. ([View Highlight](https://read.readwise.io/read/01j3k5j0zz9zd47v4qc4e7bmcv)) - Verbal primes also impact moral decision making.[33](private://read/01j3aaad80t3aar7bhc4wvy6a5/#EndnoteNumber160) As every trial lawyer knows, juries decide differently depending on how colorfully you describe someone’s act. Neuroimaging studies show that more colorful wording engages the anterior cingulate more. Moreover, people judge moral transgressions more harshly when they are described as “wrong” or “inappropriate” (versus “forbidden” or “blameworthy”). ([View Highlight](https://read.readwise.io/read/01j3m3a5fenbhks12b34d8t7y4)) - 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.” The bystander effect does occur in nondangerous situations, where the price of stepping forward is inconvenience. However, in dangerous situations, the more people present, the *more* likely individuals are to step forward. Why? Perhaps elements of reputation, where a larger crowd equals more witnesses to one’s heroics. ([View Highlight](https://read.readwise.io/read/01j3m3pyb9yb47jmfa0zhgvcxq)) - Thus, aggression is typically more about social learning than about testosterone, and differing levels of testosterone generally can’t explain why some individuals are more aggressive than others. So what does testosterone actually do to behavior? ([View Highlight](https://read.readwise.io/read/01j3m5fd33s6qjsx0n0qq8hfgd)) ## New highlights added July 27, 2024 at 8:14 AM - Moderate, transient stress (i.e., the good, stimulatory stress) promotes hippocampal LTP, while prolonged stress disrupts it and promotes LTD—one reason why cognition tanks at such times. ([View Highlight](https://read.readwise.io/read/01j3sc5kej3wnyfbb9vk4vt5d5)) ## New highlights added July 28, 2024 at 8:25 PM - Again, there’s the psychosocial angle—inequality means less social capital, less trust, cooperation, and people watching out for one another. ([View Highlight](https://read.readwise.io/read/01j3x6wtqf8rbx9c3aq53ba7zp)) - A similar conclusion comes in the 2011 book *The Better Angels of Our Nature: Why Violence Has Declined*, by Harvard’s Steven Pinker. ([View Highlight](https://read.readwise.io/read/01j3x88fv3kdb7xr03zkazynrc)) ## New highlights added July 29, 2024 at 11:02 PM - Epigenetic environmental effects on the developing brain are hugely exciting. Nonetheless, curbing of enthusiasm is needed. Findings have been overinterpreted, and as more researchers flock to the subject, the quality of studies has declined. Moreover, there is the temptation to conclude that epigenetics explains “everything,” whatever that might be; most effects of childhood experience on adult outcomes probably don’t involve epigenetics and (stay tuned) most epigenetic changes are transient. ([View Highlight](https://read.readwise.io/read/01j401bxwxnq9b3cyf3p7qgbyy)) ## New highlights added July 30, 2024 at 10:49 PM - don’t ask what a gene does; ask what it does in a particular context. ([View Highlight](https://read.readwise.io/read/01j42kjvskx4ffwc3e7vzq0z42)) ## New highlights added July 31, 2024 at 10:31 PM - Frans de Waal: “culture” is how we do and think about things, transmitted by nongenetic means. ([View Highlight](https://read.readwise.io/read/01j454eya0bd5sx1fz44z2ktkx))