Daniel Kahneman

It turns out that when you’re feeling emotionally or mentally “drained,” you’re more right on with your wording than you know.  You are actually losing real energy, in the form of blood glucose stored (in finite quantities) in the brain. Now, cutting-edge research gives us insight as to how we can grow our stores of mental energy.

In his  book, Thinking, Fast and Slow, renowned psychologist Daniel Kahneman tells the following story about eight judges in Israel:

A disturbing demonstration…was recently reported in the Proceedings of the National Academy of Sciences. The unwitting participants in the study were eight parole judges in Israel. They spend entire days reviewing applications for parole. The cases are presented in random order, and the judges spend little time on each one, an average of 6 minutes. (The default decision is denial of parole; only 35% of requests are approved. The exact time of each decision is recorded, and the times of the judges’ three food breaks–morning break, lunch, and afternoon break–during the day are recorded as well.)

The authors of the study plotted the proportion of approved requests against the time since the last food break. The proportion spikes after each meal, when about 65% of requests are granted. During the two hours or so until the judges’ next feeding, the approval rate drops steadily, to about zero just before the meal. As you might expect, this is an unwelcome result and the authors carefully checked many alternative explanations.

It’s no surprise that we get cranky when we haven’t eaten, but it is surprising and slightly alarming that judgments we assume to be wise and rational correlate with meal times.

The phenomenon is called “ego depletion,” and its implications go beyond simple changes in mood. Any brain activity that takes mental effort, like concentration, willpower, sympathy, and deliberate thought, all drain large amounts of energy from the same glucose stores. Once those store are depleted, we are less capable of mental effort and we fall back on our default, intuitive systems. These systems do not have the ability to filter or exert willpower, causing our behavior to fundamentally change.

We become irritable, easily distracted, capable of less self-control, unmindful of what we say, more likely to succumb to temptation, and show low endurance. Sound familiar? To the brain, being depleted is similar to being drunk.

You are also more susceptible to messaging and suggestion when you are depleted. It takes mental effort to keep of your guard of skepticism, or to hold contradictory ideas in your mind. By this logic, advertising that you encounter late in the day or after a workout would be more effective than it would otherwise.

It’s very interesting to note that various mental activities all deplete the brain in the same way, and that depleting the brain through one activity will lead to lower performance in a different activity. Roy Baumeister is a social psychologist who studies ego depletion. His group conducted a famous demonstration in which participants were asked to stifle their reaction to an emotionally charged movie. Afterwards they were asked to perform a physical endurance test.

The self-control it took to stifle their emotional reaction depleted their mental energy to the point where they performed poorly at the subsequent endurance test. The tired brain, having no more capacity for self-control, threw in the towel early.

So, how can we increase our stores of mental energy?

A group of scientists from Japan have found a new way to study brain energy stores, and have discovered some interesting findings. Brain energy stores are surprisingly difficult to study because the stored energy depletes instantly upon death. According to a February 22 article on the wellness blog of the New York Times, scientists at the Laboratory of Biochemistry and Neuroscience at the University of Tsukuba developed a new method of irradiating rodent brains to freeze glycogen levels at the moment of death.

The following findings will be published in this month’s Journal of Physiology:

University of Tsukuba

When the lab rat underwent a single session of physical exercise, that activity depleted the glycogen levels in the brain. When that rat was allowed to rest and feed, the glycogen not only returned, but it surpassed base levels by as much as 60%. The brain, in effect, “carbed-up.” That effect lasted for about 24 hours, and then the brain glucose stores returned to base levels.

However, when the rodent underwent four weeks of exercise sessions, the actual baseline storage amount increased. The trained-up brains had higher long-term levels of glucose on which to draw energy.