According to Tierney, the latter situation was a key one examined recently. In a report this year, two researchers looked into the decisions judges make, in an effort to account for why they rendered different judgments for defendants with identical records. After looking at the usual suspects (racism, other biases), they started to zero in on the time of day the judges made their decisions, and found that judges who made their rulings early in the day were far more likely to grant parole than those who saw a defendant late in the day. Looking even more closely, they found that if you were unlucky enough to appear before a judge just before the noon break, or just before closing time, you would likely have your parole plea rejected; if you saw the judge at the beginning of the day, or right after lunch, you were more likely to get your parole granted. The cause: decision fatigue. As the researchers noted, “the mental work of ruling on case after case, whatever their individual merits, wore them down.”
What this and other experiments have demonstrated is that each of us possesses “a finite store of mental energy for exerting self-control.” And self-control requires that old bugaboo “will power”—a form of mental energy that can, and often is, exhausted. If you’ve spent your day resisting desire—whether it’s a yen for a cigarette, a candy bar, or a trip onto the internet—you’re less capable of resisting other temptations. Nor is this just a curious finding. What researchers argue is that this kind of decision fatigue is “a major—and hitherto ignored—factor in trapping people in poverty.” People who are poor, that is, constantly have to make that hardest of decisions, the trade-off (can I afford this? can I afford that? Should I pay the gas bill or buy good food?), and such decisions sap their energies for other efforts like school, work or improving their job prospects. This is confirmed by images that have long been used to condemn the poor for their failure of effort: welfare mothers buying junk food, or indulging in snacks while shopping. Far from being a condemnation of “weak character,” however, such activities often indicate decision fatigue, which the poor experience more than the rich because of the increased number of trade-offs their lives require, and hence the decreased willpower left them to resist impulse buying.
The big surprise in this research, though, comes with the brain studies. Everyone knows that the brain is a great consumer of sugar, or glucose, for energy. But what no one had expected was the specific connection between glucose supply and willpower. In a series of experiments, researchers tested this by refueling the brains of some subjects performing tasks with sugary lemonade (glucose), and some with lemonade sweetened with diet sweetener (no glucose.) The results were clear: those who got the glucose found their willpower restored, and thus their ability to exercise self-control augmented. They made better choices, and even when asked to make financial decisions, they focused on long-term strategy rather than opting for a quick payoff. In short, more mental energy allowed them to persist in whatever task was at hand. Even more to the point, the researchers found that the effect of glucose was specific to certain areas of the brain. As Tierney puts it:
Your brain does not stop working when glucose is low. It stops doing some things and starts doing others. It responds more strongly to immediate rewards, and pays less attention to long-term prospects.
This is critical information, especially in our choice-and-distraction-filled culture. Yet another study in Germany, where subjects were monitored by frequently reporting their activity via their Blackberries, concluded that people at work spend as much as 4 hours a day “resisting desire.” The most common of these desires were “urges to eat and sleep, followed by the urge for leisure” (i.e. taking a break by playing a computer game, etc.). Sexual urges were next on the list, slightly higher than checking Facebook or email. The most popular general type of desire was to find a distraction—and of course, the workplace of large numbers of people these days centers on the computer, that click-of-the-mouse distraction machine.
And the trouble with all this is that willpower depletion doesn’t manifest with a specific symptom, like a runny nose, or a pain in the gut. As Tierney says:
Ego depletion manifests itself not as one feeling but rather as a propensity to experience everything more intensely. When the brain’s regulatory powers weaken, frustrations seem more irritating than usual. Impulses to eat, drink, spend and say stupid things feel more powerful.
Perhaps this is why tired politicians so often say, and do stupid things. Not to mention the howlers of our physicians, our generals, our corporate execs, and our media pundits. Perhaps, too, it explains why Ronald Reagan always kept a jar of jellybeans on his desk—though it is true that his decision-making stemmed from a malady of a different sort.
In any case, the lesson from all this might be: take breaks. Eat candy (or better still, protein). And don’t make important decisions when you’re exhausted (like responding to that nasty email). Most decisions can wait, and will profit from a glucose-rich, rather than a glucose-depleted brain.