Self-Control and the Prefrontal 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.

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I love this post and like many of your posts find it applicable to my own life, but i find it curious that you focus on self-control only in regard to not doing something and avoid discussing a more active self-control. I find that i'm good at saying to no to a lot of things i don't need (unnecessary spending, the one more drink, etc.) but i'm terrible when it comes to things that require action (working on grad school apps for example) even though both have to do with long-term goals. How are the two related? How are they different?

By matthew chapman (not verified) on 23 Oct 2008 #permalink

This is one of those beautiful psychological experiments that makes me go "OH! So that's why I act that way!". It also seems kind of obvious in retrospect, but I doubt I would have ever put it together like that.

Maybe this is why doing a PhD seems to be more about persistance than intellect per se... ability to apply intellect depends on self-discipline being applied appropriately.
I do wonder about the marshamallow kids though. It may be that the sorts of kids who can deny themseles marshmallows are also the sorts to be more teacher-pleasing (thus benefiting their grades), but would not be able to exercise self-discipline outside of a context where somebody is watching.
Did the people in this study know they were being observed in their snacking choices?

Our neuropyschologist recently was addressing this very issue with us about our daughter who has FAS (fetal alcohol syndrome.) In my daughter's case we puzzled over her strange behaviors, she would occasionally stop using her words and bark like a dog for her communication style. She would obsessively eat things that weren't food, mostly paper. She would pull a strand of hair out of her head and run it through her mouth over and over and over.

The neuropsych suggested that at these times our daughter's functioning was centered in her mid brain and the frontal cortex was "offline." The neuropysch stressed that we needed to find a way to stop overtaxing the frontal cortex so she wouldn't retreat to her mid brain. We adjusted the school demands, we adjusted the home demands and voila', we've seen a great reduction in those strange behaviors. In fact many of them have completely disappeared.

The hope for our daughter, is that if we can keep her functioning in her frontal cortex at a low level of demand, we can increase her overall ability to function on a daily basis. This research seems to point exactly in that direction, reduce the load and the frontal cortex performs better.

We go a step further in our hope. If she spends more time in her frontal cortex then maybe she's building more pathways, which could lead to higher functioning. We can't reverse the organic damage but maybe we can build a brain that can work around it.

"Fifty-nine percent of the people trying to remember seven digits (high load) chose the cake, while sixty-three percent..."

That seems very inconclusive to me. Unless a large number of people was used, looks like a statistical fluctuation.

Looks like it was 59% one way in one group, and 63% the other way in the other group, a 22% spread.

The Shiv experiment seems to corroborate our day-to-day experience (at least for many of us I'm sure). Yet I can't help but wonder if the actual reason for the decrease in self-control after subsequent "uses" is really excess stress on the lower limbic/dopaminergic structures rather than merely running out of "thinking resources". In other words, couldn't the experiment be seen in the light of participants undergoing emotional stress rather than intellectual depletion? If participants could somehow manage to lower their stress when faced with temptation AND when faced with having to remember something, I would speculate they might easily have a higher intellectual threshold.

I wonder how much of that "delayed gratification" is actually slower decision making process. I suspect that there's a learning/planning speed vs depth trade-off in the neocortex, related to average connectivity range among minicolumns. If your planning / decision-making is relatively slow, you'd automatically focus on longer-range consequences. I have some speculations on these trade-offs in my knol: http://knol.google.com/k/boris-kazachenko/cognitive-focus-cortical-mini…

I tend to see patterns and applications for information.

What immediately came to mind were the problems in our society with substance abuse (bad choices!). Substance abuse can also include food.

Although there are probably many other reasons, our stress filled and hurried lives as we race from one commitment to another, and the previously unimagined amount of information that we are bombarded with, including by choice through television, radio, signage, cell phones and the Internet could account for some of these problems.

Very interesting finding. Thanks.
Judy Rey

The first paragraph of the article says "...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..." but it wasn't the ability to resist the temptation of a second marshmallow at all. It was the ability to resist the temptation of a FIRST marshmallow in order to get a SECOND marshmallow.

At that point, presumably, resistance to temptation breaks down completely and both marshmallows are consumed.

There are probably many other reasons, our stress filled and hurried lives as we race from one commitment to another, and the previously unimagined amount of information that we are bombarded with, including by choice through television, radio, signage, cell phones and the Internet could account for some of these problems.

but it wasn't the ability to resist the temptation of a second marshmallow at all. It was the ability to resist the temptation of a FIRST marshmallow in order to get a SECOND marshmallow.

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Grrrr.... Mike and Amy are more correct here. There is no way offering a sugar glucose hit to a taxed brain should be compared to the lesser glucose hit of fruit. The taxed brain is what is making the decision and perhaps it needed glucose fast... and was taking care of its needs, which is what we really need to discover about out brains.

What really bothers me about science being taken as absolutes is that is what stagnates further and meaningful research. The brain controls us until we learn how our brain works, so do not make people believe what may not be true.

Take this as an interesting tidbit of science, but not necessarily a "truth." When they have mapped the brain and how we can stimulate areas ourselves, cheaply scan it, heal it, feed it, rejuvenate it, eat to strengthen it, in crease blood blow to and through it, control it, etc... (read Dr Amen's books for a lot more insight then this type of article) then we might be able to have aha moments on the brain.

Until then it is still far to much a mystery to pretend this study has more meaning then a brain needing a glucose hit.

By youniquelikeme (not verified) on 29 Apr 2011 #permalink

Correction: "too" much a mystery.

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