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October 29 - December 9, 2023
By early adolescence, the brain is a fairly close approximation of the adult version, with adult densities of neurons and synapses, and the process of myelinating the brain already achieved. Except for one brain region which, amazingly, won’t fully mature for another decade. The region? The frontal cortex, of course. Maturation of this region lags way behind the rest of the cortex—to some degree in all mammals, and dramatically so in primates.[29]
By definition, if the frontal cortex is the last part of the brain to develop, it is the brain region least shaped by genes and most shaped by environment.
If this is the brain region central to doing the right thing when it’s the harder thing to do, no genes can specify what counts as the right thing. It has to be learned the long, hard way, by experience.
What sorts of influences effect maturation?
Parenting, of course.
Peer socialization,
Environmental influences.
Cultural beliefs and values,
If we are evolutionary biologists thinking about human behavior, by definition we’re also being behavior geneticists, developmental neurobiologists, and neuroplasticians (spell-check just went crazy). This is because evolving means changes in what variants of genes you find in organisms and thus the ways in which they shape brain construction.
In the words of legal scholar Pete Alces, there is “no remaining gap between nature and nurture for moral responsibility to fill.”
the view forcefully argued by philosopher Neil Levy in his 2011 book, Hard Luck: How Luck Undermines Free Will and Moral Responsibility (Oxford University Press). He focuses on two categories of luck. One, present luck, examines its role in the difference between driving while so drunk that, when coupled with events in the seconds to minutes before, you would have killed someone if they had happened to be crossing the street, and the bad luck of being in that state and actually killing someone.
“it is not ontology that rules out free will, it is luck (his emphasis).”[*] In his view, not only does it make no sense to hold us responsible for our actions; we also had no control over the formation of our beliefs about the rightness and consequences of that action or about the availability of alternatives. You can’t successfully believe something different from what you believe.[*]
Neil Levy.
“Do Pedophiles Deserve Sympathy?” Psychologist James Cantor of the University of Toronto reviewed the neurobiology of pedophilia. The wrong mix of genes, endocrine abnormalities in fetal life, and childhood head injury all increase the likelihood. Does this raise the possibility that a neurobiological die is cast, that some people are destined to be this way? Precisely. Cantor concludes correctly, “One cannot choose to not be a pedophile.” But then he does an Olympian leap across the Grand Canyon–size false dichotomy of compatibilism. Does any of that biology lessen the condemnation and
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Bragging for the frontal cortex, it’s the newest part of the brain; we primates have, proportionately, more of it than other mammals; when you examine gene variants that are unique to primates, a disproportionate percentage of them are expressed in the frontal cortex. Our human frontal cortex is proportionately bigger and/or more complexly wired than that of any other primate.
it’s the last part of the brain to fully mature, not being fully constructed until your midtwenties; this is outrageously delayed, given that most of the brain is up and running within a few years of birth.
Frontal cortex.
the most interesting part of the frontal cortex—the prefrontal cortex (PFC)—is proportionately even larger than the rest of the frontal cortex, and more recently evolved.[*],[10] As a reminder, the PFC is central to executive function, decision-making. We saw this in chapter 2, where, way up in the chain of Libetian commands, there was the PFC making decisions up to ten seconds before subjects first became aware of that intent. What the PFC is most about is making tough decisions in the face of temptation—gratification postponement, long-term planning, impulse control, emotional regulation.
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“Doing the right thing” requires two different skills from the PFC. There’s sending the decisive “do this” signal along the path from the PFC to the frontal cortex to the supplementary motor area (the SMA of chapter 2) to the motor cortex. But even more important, there is the “and don’t do that, even if that’s the usual” signal. Even more than sending excitatory signals to the motor cortex, the PFC is about inhibiting habitual brain circuits. To hark back again to chapter 2, the PFC is central to showing that we lack both free will and the conscious veto power of free won’t.[11]
Neuroimaging studies show the PFC reining in more emotional brain regions in the name of doing (or thinking) the right thing. Stick a volunteer in a brain scanner and flash up pictures of faces. And in a depressing, well-replicated finding, flash up the face of someone of another race and in about 75 percent of subjects, there is activation of the amygdala, the brain region central to fear, anxiety, and aggression.[*] In under a tenth of a second.[*] And then the PFC does the harder thing. In most of those subjects, a few seconds after the amygdala activates, the PFC kicks in, turning off the
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The PFC handles April 15; the limbic system, February 14. The former makes you grudgingly respect Into the Woods; the latter makes you tearful during Les Mis, despite knowing that you’re being manipulated. The former is engaged when juries decide guilt or innocence; the latter, when they decide how much to punish the guilty.[19] But—and this is a truly key point—rather than the PFC and limbic system either being in opposition or ignoring each other, they are usually intertwined. In order to do the correct, harder thing, the PFC requires a huge amount of limbic, emotional input.
the dorsolateral PFC (dlPFC), the definitive rational decider in the frontal cortex. Like a Russian nesting doll, the cortex is the newest part of the brain to evolve, the frontal cortex is the newest part of the cortex, the PFC is the newest part of the frontal cortex, and the dlPFC is the newest part of the PFC. The dlPFC is the last part of the PFC to fully mature. The dlPFC is the essence of the PFC as tight-assed superego. It’s the most active part of the PFC during “count the months backward” tasks, or when considering temptation. It is fiercely utilitarian—more dlPFC activity during a
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(a) grit, character, backbone, tenacity, strong moral compass, willing spirit winning out over weak flesh, are all produced by the PFC; (b) the PFC is made of biological stuff identical to the rest of your brain; (c) your current PFC is the outcome of all that uncontrollable biology interacting with all that uncontrollable environment.
Fatigue also depletes frontal resources. As the workday progresses, doctors take the easier way out, ordering up fewer tests, being more likely to prescribe opiates (but not a nonproblematic drug like an anti-inflammatory, or physical therapy). Subjects are more likely to behave unethically and become less morally reflective as the day progresses, or after they’ve struggled with a cognitively challenging task. In an immensely unsettling study of emergency room doctors, the more cognitively demanding the workday (as measured by patient load), the higher the levels of implicit racial bias by the
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researchers studied a group of judges overseeing more than a thousand parole board decisions. What best predicted whether a judge granted someone parole versus more jail time? How long it had been since they had eaten a meal. Appear before the judge soon after she’s had a meal, and there was a roughly 65 percent chance of parole; appear a few hours after a meal, and there was close to a 0 percent chance.[*],[28]
all sorts of things often out of your control—stress, pain, hunger, fatigue, whose sweat you’re smelling, who’s in your peripheral vision—can modulate how effectively your PFC does its job. Usually without your knowing it’s happening. No judge, if asked why she just made her judicial decision, cites her blood glucose levels. Instead, we’re going to hear a philosophical discourse about some bearded dead guy in a toga.
traumatic brain injury (TBI—à
Roughly half the people incarcerated for violent antisocial criminality have a history of TBI, versus about 8 percent of the general population; having had a TBI increases the likelihood of recidivism in prison populations.
Chapter 3 provided the basic facts: (a) when you’re an adolescent, your PFC still has a ton of construction ahead of it; (b) in contrast, the dopamine system, crucial to reward, anticipation, and motivation, is already going full blast, so the PFC hasn’t a prayer of effectively reining in thrill seeking, impulsivity, craving of novelty, meaning that adolescents behave in adolescent ways; (c) if the adolescent PFC is still a construction site, this time of your life is the last period that environment and experience will have a major role in influencing your adult PFC;[*] (d) delayed
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an enriched, stimulating environment during adolescence has great effects on the resulting adult PFC and can reverse some of the effects of childhood adversity. For example, an enriched environment during adolescence causes permanent changes in gene regulation in the PFC, producing higher adult levels of neuronal growth factors like BDNF. Furthermore, while prenatal stress causes reductions in BDNF levels in the adult PFC (stay tuned), adolescent enrichment can reverse this effect. All changes that impair the PFC’s ability for impulse control and gratification postponement. So if you want to
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“whatever adolescence has handed you,” replace adolescence with childhood, and underline the paragraph eighteen more times. Whaddaya know, the sort of childhood you had shapes the construction of the PFC at the time and the sort of PFC you’ll have in adulthood.[*]
childhood abuse produces kids with a smaller PFC, with less gray matter and with changes in circuitry: less communication among different subregions of the PFC, less coupling between the vmPFC and the amygdala (and the bigger the effect, the more prone the child is to anxiety). Synapses in the brain are less excitable; there are changes in the numbers of receptors for various neurotransmitters and changes in gene expression and patterns of epigenetic marking of genes—along with impaired executive function and impulse control in the child.
Childhood abuse produces an adult PFC that is smaller, thinner, and with less gray matter, altered PFC activity in response to emotional stimuli, altered levels of receptors for various neurotransmitters, weakened coupling between both the PFC and dopaminergic “reward” regions (predicting increased depression risk), and weakened coupling with the amygdala as well, predicting more of a tendency to respond to frustration with anger (“trait anger”). And once again, all of these changes are associated with an adult PFC that isn’t at its best.[43]
lower socioeconomic status predicts a less stimulating environment for a child—all those enriching extracurricular activities that can’t be afforded, the world of single mothers working multiple jobs who are too exhausted to read to their child. As one shocking manifestation of this, by age three, your average high-socioeconomic status kid has heard about thirty million more words at home than a poor kid, and in one study, the relationship between socioeconomic status and the activity of a child’s PFC was partially mediated by the complexity of language use at home.[47]
A crucial point about genes related to brain function (well, pretty much all genes) is that the same gene variant will work differently, sometimes even dramatically differently, in different environments. This interaction between gene variant and variation in environment means that, ultimately, you can’t say what a gene “does,” only what it does in each particular environment in which it has been studied.
The section on adolescence considered why dramatic delayed maturation of the PFC evolved in humans and how that makes that region’s construction so subject to environmental influences.
East Asian collectivism is generally thought to arise from the communal work demands of floodplain rice farming. Recent Chinese immigrants to the United States already show the Western distinction between activating your vmPFC when thinking about yourself and activating it when thinking about your mother. This suggests that people back home who were more individualistic were the ones more likely to choose to emigrate, a mechanism of self-selection for these traits.[57]
No matter how thinly you slice it, each unique biological state was caused by a unique state that preceded it.
two ways people mistakenly believe they’ve found free will in chaotic systems. First is the idea that if you start with something simple in biology and, unpredictably, out of that comes hugely complex behavior, free will just happened. Second is the belief that if you have a complex behavior that could have arisen from either of two different preceding biological states and there’s no way to ever tell which one caused it, then you can get away with claiming that it wasn’t caused by anything, that the event was free of determinism.
reductionism, the idea that to understand something complicated, break it down into its component parts, study them, add your insights about each component part together, and you will understand the complicated whole. And if one of those component parts is itself too complicated to understand, study its eensy subcomponent parts and understand them.
chaos theory is a horrible name, insofar as it is about the opposite of nihilistic chaos and is instead about the patterns of structure hidden in seeming chaos.
A cell, a brain, a person, a society, was more like the chaoticism of a cloud than the reductionism of a watch.[1]
So a bunch of thinkers find free will in the structure of chaoticism. Compatibilists and incompatibilists debate whether free will is possible in a deterministic world, but now you can skip the whole brouhaha because, according to them, chaoticism shows that the world isn’t deterministic.
critical mistake running through all of this: determinism and predictability are very different things. Even if chaoticism is unpredictable, it is still deterministic.
The previous two chapters can basically be distilled to the following: —“Break it down to its component parts” reductionism doesn’t work for understanding some vastly interesting things about us. Instead, in such chaotic systems, minuscule differences in starting states amplify enormously in their consequences. —This nonlinearity makes for fundamental unpredictability, suggesting to many that there is an essentialism that defies reductive determinism, meaning that the “there can’t be free will because the world is deterministic” stance goes down the drain. —Nope. Unpredictable is not the same
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The Traveling Slime Mold. Here’s the thing that makes the audience shout for more—the wall outlines the coastline around Tokyo; the slime was plopped onto where Tokyo would be, and the oat flakes corresponded to the suburban train stations situated around Tokyo. And out of the slime mold emerged a pattern of tubule linkages that was statistically similar to the actual train lines linking those stations. A slime mold without a neuron to its name, versus teams of urban planners.[13]
Each cell in your body is at most only a few cells away from a capillary, and the circulatory system accomplishes this by growing around forty-eight thousand miles of capillaries in an adult.
