The Frontal Cortex

Yesterday was Yom Kippur, the Jewish holiday of atonement. It's traditional to fast on Yom Kippur for all the usual religious reasons - not eating is a way to elevate the spirit and purify the mind (or so says the Talmud). It makes the sacred day feel a little less ordinary.

I have to confess: I'm a terrible faster. When I don't eat, my thoughts don't become more ethereal and holy - they become fixated on calories, so that the only thing I can listen to is the impatient gurgling of my stomach. (My belly drowns out the sermon.) I get cranky and tired and squander hours daydreaming about ice cream - my wife tells me that I regress into a five year old. (After a single day of fasting, I'm in awe of Muslims who fast for the entire month of Ramadan. I have no idea how they do it.)

This year, I pledged to act more mature. I promised myself I wouldn't complain about not being able to eat. So how would I distract myself from thoughts of the fridge? I decided to work on an article during the afternoon and pledged to spend a few hours playing with sentences (not very holy, I know.) It didn't take long, however, before I realized that I was wasting my time - I was utterly unable to focus or think in clear thoughts; my prose was even more more garbled than usual. I then decided to read a few papers for work. Once again, my mind rejected the premise: after a few paragraphs of dense prose, I was fast asleep, kidnapped by a nap.

For me, the lesson was rather obvious: my brain needs glucose like my laptop needs alternating current. Even a few hours without food means that I'm running on reserve power; I could feel my executive function (and my frontal lobes) begin to sputter and quit. And then I passed out.

This reminded me of a clever study I describe in How We Decide:

Look, for example, at this experiment led by psychology graduate student E.J. Masicampo and Roy Baumeister, an eminent psychologist at Florida State University. The experiment began with a large group of undergraduates performing a mentally taxing activity that involved watching a video while ignoring the text of random words scrolling on the bottom of the screen. (It takes conscious effort to not pay attention to salient stimuli.) The students were then offered some lemonade. Half of them got lemonade made with real sugar, and the other half got lemonade made with a sugar substitute. After giving the glucose time to enter the bloodstream and perfuse the brain (about fifteen minutes), Baumeister had the students make decisions about apartments. It turned out that the students who were given the drink without real sugar were significantly more likely to rely on instinct and intuition when choosing a place to live, even if that led them to choose the wrong places. [The experiments assessed this by looking at their vulnerability to the "attraction effect," which occurs when a difficult choice is swayed by the presence of an irrelevant decoy option.] The reason, according to Baumeister, is that the parts of the brain responsible for careful, rational deliberation were simply too exhausted to think. They'd needed a restorative sugar fix, and all they'd gotten was Splenda. This research can also help explain why we get cranky when we're hungry and tired: the brain is less able to suppress the negative emotions sparked by small annoyances.

I'd love to see a comparative survey of how decisions change in Muslim countries during Ramadan. Given the Baumeister experiment, you'd expect to see a slight but consistent rise in the sorts of choices that tend to be associated with impulse, instinct and the reliance on lazy heuristics. Are people running more red lights? Making more impulse purchases on their credit card? Engaging in more stereotyping? The irony of fasting is that, although we think we're engaging in act of strict self-control, we're actually making it harder to resist other temptations. For a thorough survey of the relationship between self-control and glucose, check out this extensive review article, "Self-Control Relies on Glucose As A Limited Energy Source: Willpower is More Than A Metaphor".