The brain area largely responsible for willpower, the prefrontal cortex, is located just behind the forehead. While this bit of tissue has greatly expanded during human evolution, it probably hasn’t expanded enough. That’s because the prefrontal cortex has many other things to worry about besides New Year’s resolutions. For instance, scientists have discovered that this chunk of cortex is also in charge of keeping us focused, handling short-term memory and solving abstract problems. Asking it to lose weight is often asking it to do one thing too many.
In one experiment, led by Baba Shiv at Stanford University, several dozen undergraduates were divided into two groups. One group was given a two-digit number to remember, while the second group was given a seven-digit number. Then they were told to walk down the hall, where they were presented with two different snack options: a slice of chocolate cake or a bowl of fruit salad.
Here’s where the results get weird. The students with seven digits to remember were nearly twice as likely to choose the cake as students given two digits. The reason, according to Prof. Shiv, is that those extra numbers took up valuable space in the brain—they were a “cognitive load”—making it that much harder to resist a decadent dessert. In other words, willpower is so weak, and the prefrontal cortex is so overtaxed, that all it takes is five extra bits of information before the brain starts to give in to temptation.
This helps explain why, after a long day at the office, we’re more likely to indulge in a pint of ice cream, or eat one too many slices of leftover pizza. (In fact, one study by researchers at the University of Michigan found that just walking down a crowded city street was enough to reduce measures of self-control, as all the stimuli stressed out the cortex.) A tired brain, preoccupied with its problems, is going to struggle to resist what it wants, even when what it wants isn’t what we need.
Probably why during certain times of the year, like right now, when my brain is over-stimulated by work, I tend to keep my liver busy cleaning wine and other inebriants out of my blood stream. I knew there had to be a scientific reason.
In a 2002 experiment, led by Mark Muraven at the University at Albany, a group of male subjects was asked to not think about a white elephant for five minutes while writing down their thoughts. That turns out to be a rather difficult mental challenge, akin to staying focused on a tedious project at work. (A control group was given a few simple arithmetic problems to solve.) Then, Mr. Muraven had the subjects take a beer taste test, although he warned them that their next task involved driving a car. Sure enough, people in the white elephant group drank significantly more beer than people in the control group, which suggests that they had a harder time not indulging in alcohol.
The implications of this muscle metaphor are vast.…
In a 2007 experiment, Prof. Baumeister and his colleagues found that students who fasted for three hours and then had to perform a variety of self-control tasks, such as focusing on a boring video or suppressing negative stereotypes, had significantly lower glucose levels than students who didn’t have to exert self-control. Willpower, in other words, requires real energy.
- which I own, but haven’t gotten a chance to read yet [↩]