Crazy—or just sleepy?
People who don’t get enough sleep act as if they’re mentally ill, falling prey to wild emotional swings, says a new study. Researchers performed brain scans on two groups of young, healthy people, half of whom were deprived of sleep for just one night. When the subjects were shown a series of images ranging from benign to disturbing (a tarantula on someone’s shoulder, an attacking shark, disfigured burn victims), the people who had slept well the night before acted normally: Their brains interpreted the resulting fear and disgust in context, so they remained relatively calm. But the sleep-deprived brains went haywire, sending lots of panicky signals to the brain stem, which manages primitive fight-or-flight responses. These sleep-deprived people, in fact, exhibited the kind of emotional instability usually seen in the mentally ill, laughing wildly one minute and crying hysterically the next. “The emotional parts of the brain just seem to run amok,” University of California at Berkeley neuroscientist Matthew Walker tells USA Today.

Previous research has found that people with mental illness are often chronically sleep-deprived, and psychologists had assumed that it was the illness causing the sleep problems. Now they think it could be the other way around. The current epidemic of depression and other mental illness among teens, some psychologists say, could be related to the frenetic multitasking and resulting lack of sleep now common in this age group.