The Frontal Cortex

There's a new scientific appreciation for the importance of self-control. This trend began with Walter Mischel's astonishing marshmallow experiments, in which the ability of a four-year old to resist the temptation of a second marshmallow turned out to be a better predictor of future academic success than his or her IQ score. In other words, willpower trumped raw intelligence.

But what cortical muscles are behind self-control? An excellent Boston Globe article summarizes some current research and future projects:

Most recently, Yale University researchers found that delaying gratification involves an area of the brain, the anterior prefrontal cortex, that is known to be involved in abstract problem-solving and keeping track of goals. For example: You want to drive across town, so you find your keys, start your car, and navigate the route, all while that critical brain region keeps the overarching trip goal in your mind.

The brain scan findings from 103 subjects suggest that delaying gratification involves the ability to imagine a future event clearly, said Jeremy Gray, a Yale psychology professor and coauthor of the study in the September edition of the journal Psychological Science. You need "a sort of 'far-sightedness,' to put it in a single word," he said.

The problem with relying on the prefrontal cortex (PFC) for self-control, of course, is that the PFC is a relatively feeble bit of brain, at least when compared to the limbic/dopaminergic inputs coming from below. Consider this clever experiment, led by Stanford professor Baba Shiv. (I've blogged about this experiment before.) Shiv was curious whether "cognitive load" could influence self-control, so he gave half of the subjects a two-digit number to memorize (low load), while the other half were given a seven-digit number (high load). Subjects were then instructed to walk to another room in the building. On the way they passed by a table at which they were presented with a choice between a caloric slice of chocolate cake or a bowl of fruit salad. Fifty-nine percent of the people trying to remember seven digits (high load) chose the cake, while sixty-three percent of the two-digit subjects (low load) chose the fruit salad. In other words, having people memorize an extra five digits made them exhibit significantly less self-control.

Why did the number of digits have such a strong effect? Shiv speculates that the effort required to memorize seven numbers drew cognitive resources away from our ability to control our urges. This makes anatomical sense, since working memory and self-control are both located in our prefrontal cortex. Having to remember seven numbers occupied neurons that would otherwise help us decide what to eat, which causes us to become more reliant on our impulsive emotions. While we tend to think of self-control as being an innate trait, it is actually dependent on a range of extrinsic factors, all of which affect the way our brain responds to a given situation.

This model of limited "thinking resources" has now generated a large amount of supporting evidence. Our decisions really are swayed by the computational limits of our brain. For example, in 2003 neuroeconomists noticed that subjects on diets who resisted temptation in the morning (by foregoing the chance to grab snacks from a nearby basket) later ate significantly more ice cream in an ice-cream taste test than subjects who hadn't exercised self-control. They also quit 40 percent earlier when confronted with a difficult math problem. By resisting the morning snacks, they had temporarily "used up" their ability to resist further temptation. (Other variables that seem to exhaust our self-control are alcohol, stress, and sleep deprivation.)

The moral of this data is that we have to pick our battles. Everybody occasionally splurges on the slice of cake, or quickly gives up on a difficult problem. Instead of trying to never be bad, we should focus on being good when it matters. Your PFC gets tired rather quickly.