robert_sapolsky's picture
Neuroscientist, Stanford University; Author, Behave
What s the neurobiology of doing good and being good?


I've spent most of my career as a neurobiologist working on an area of the brain called the hippocampus. It's a fairly useful region — it plays a critical role in learning and memory. It's the area that's damaged in Alzheimer's, in alcoholic dementia, during prolonged seizures or cardiac arrest. You want to have your hippocampus functioning properly. So I've spent all these years trying to figure out why hippocampal neurons die so easily and what you can do about it. That's fine, might even prove useful some day. But as of late, it's been striking me that I'm going to be moving in the direction of studying a part of the brain called the prefrontal cortex (PFC).

It's a fascinating part of the brain, the part of the brain that most defines us as humans. There's endless technical ways to describe what the PFC does, but as an informal definition that works pretty well, it's the closest thing we have to a superego. The PFC is what allows us to become potty trained early on. And it is responsible for squeezing our psychic sphincters closed as well. It keeps us from belching loudly at the quiet moment in the wedding ceremony, prevents us from telling our host just what we really think of the inedible meal they've served. It keeps us from having our murderous thoughts turn into murderous acts. And it plays a similar role in the cognitive realm — the PFC stops us from falling into solving a problem with an answer that, while the easier, more reflexive one, is wrong. The PFC is what makes us do the right thing, even if it's harder.

Not surprisingly, it's one of the last parts of the brain to fully develop (technical jargon — to fully myelinate). But what is surprising is just how long it is before the PFC comes fully on line — astonishingly, around age 30. And this is where my question comes in. It is best framed in the context of young kids, and this is probably what has prompted me to begin to think about the PFC, as I have two young children. Kids are wildly "frontally disinhibited," the term for having a PFC that hasn't quite matured yet into keeping its foot firmly on the brake. Play hide and seek with a three year old, loudly, plaintively call, "Where are you," and their lack of frontal function does them in — they can't stop themselves from calling out — Here I am, under the table — giving away their hiding spot. I suspect that there is a direct, near linear correlation between the number of fully myelinated frontal neurons in a small child's brain and how many dominoes you can line up in front of him before he must MUST knock them over.

So my question comes to the forefront in a scenario that came up frequently for me a few years ago: my then three year old who, while a wonderful child, was distinctly three, would do something reasonably appalling to his younger sister — take some stuffed animal away, grab some contested food item, whatever. A meltdown then ensues. My wife or I intervene, strongly reprimanding our son for mistreating his sister. And then the other parent would say, "Well, is this really fair to be coming down on him like this?, after all, he has no frontal function yet, he can't stop himself" (my wife is a neuropsychologist so, pathetically, we actually speak this way to each other). And the other would retort — "Well, how else is he going to develop that frontal function?"

That's the basic question — how does the world of empathy, theory of mind, gratification postponement, Kohlberg stages of moral development, etc., combine with the world of neurotrophic growth factors stimulating neurons to grow fancier connections? How do they produce a PFC that makes you do the harder thing because it's right? How does this become a life-long pattern of PFC function