It's no surprise that sleep deprivation is bad for emotional stability -- oh, how it makes you cranky. But until now, scientists haven't really understood why.
In what is the first neural investigation into what happens to the sleep-deprived brain, researchers at UC-Berkeley used functional Magnetic Resonance Imaging (fMRI) to look how activity in the amygdala, a brain region key to processing emotions, is affected by sleep deprivation. When subjects who had stayed awake for 35 hours were shown negative visual stimuli like mutilated bodies, the amygdala become hyperactive compared to subjects who had gotten a full night's sleep. And when the amygdala goes haywire, it consequently shuts down the prefrontal cortex, an area responsible for logical reasoning, preventing the release of chemicals needed to calm down the fight-or-flight reflex.
The amygdala is also closely connected to depression, anxiety and other psychiatric disorders. It could be that without sleep, the brain reverts back to more primitive patterns of activity, unable to put emotional experiences into context and produce controlled, appropriate responses, according to Matthew Walker, director of UC Berkeley's Sleep and Neuroimaging Laboratory and senior author of the study.
The study's findings lay the groundwork for further investigation into the relationship between sleep and psychiatric illnesses. Clinical evidence, for example, has shown that some form of sleep disruption is present in almost all psychiatric disorders; this is the first set of experiments demonstrating that even healthy people's brains mimic certain pathological psychiatric patterns when deprived of their 40 winks.