The PFC is famously the last part of the brain to mature; it’s not fully constructed in humans until we’re in our mid-20s. Not because it’s harder to build—it’s made of the same components as the rest of the brain, which has been largely functional for the past couple of decades. Rather, Sapolsky claims that it matures late specifically to enable it to become the brain region most influenced by the experiences we have in those first two decades—to learn from those experiences and have them shape us. Grit, pluck, willpower, stick-to-it-iveness, and self-restraint are controlled by the PFC and are shaped by the environment we grew up in. And that’s an environment we do not choose or control.
“What the PFC is most about is making tough decisions in the face of temptation—gratification postponement, long-term planning, impulse control, emotional regulation,” he writes. “The PFC is essential for getting you to do the right thing when it is the harder thing to do.”
Difficult decisions take a ton of mental energy. That’s not a metaphor; the PFC consumes an immense amount of cellular energy. So much so that if you’re hungry, tired, stressed, or lack resilience because you were born poor, which gave you chronically elevated glucocorticoid levels, your PFC simply does not have the juice to make good decisions when it matters. Sapolsky points out that “a substantial percentage of people incarcerated for violent crime have a history of concussive head trauma to the PFC.”
An ambitious goal
“This book has a goal,” Sapolsky writes. “To get people to think differently about moral responsibility, blame, and praise.” Although the world is wholly deterministic, we can, and have, learned to change our views and behaviors—both on the individual and the societal levels. We learn and we change when our environment modulates the same molecules, genes, and neuronal pathways that controlled our original views and behaviors. Incidentally, these are the same molecules, genes, and neuronal pathways modulated when a sea slug learns to avoid being shocked by a researcher—i.e., not free will.
