Ever wondered why you feel grumpy after a bad night's sleep? Well, researchers from University of California, Berkeley, and Harvard Medical School have resolved the mystery, by discovering that a lack of sleep causes the brain's emotional centers to significantly overreact to negative experiences.
In the first neural investigation into what happens to the emotional brain without sleep, results from the brain imaging study suggest that while a good night's rest can regulate your mood and help you cope with the next day's emotional challenges, sleep deprivation does the opposite by excessively boosting the part of the brain most closely connected to depression, anxiety and other psychiatric disorders.
"It's almost as though, without sleep, the brain had reverted back to more primitive patterns of activity, in that it was unable to put emotional experiences into context and produce controlled, appropriate responses," said Matthew Walker, director of UC Berkeley's Sleep and Neuroimaging Laboratory and senior author of the study.
"Emotionally, you're not on a level playing field," he added.
Walker and his team found that the reason behind the phenomenon is the amygdala, the region of the brain that alerts the body to protect itself in times of danger. Walker said that amygdala goes into overdrive on no sleep, consequently shuting down the prefrontal cortex, which commands logical reasoning, and thus preventing the release of chemicals needed to pacify the fight-or-flight reflex.
Using functioning Magnetic Resonance Imaging (fMRI), Walker and his team found that the amygdala, which is also a key to processing emotions, became hyperactive in response to negative visual stimuli - mutilated bodies, children with tumors and other gory images - in study participants who stayed awake for 35 hours straight. Conversely, brain scans of those who got a full night's sleep in their own beds showed normal activity in the amygdala.
"The emotional centers of the brain were over 60 percent more reactive under conditions of sleep deprivation than in subjects who had obtained a normal night of sleep," Walker said.
The study included 26 healthy people who were assigned to either a normal sleep group or to a sleep deprivation group, where they were kept awake for 35 hours. Afterwards, functional magnetic resonance imaging (fMRI) was used to measure the participants' brain activity. Walker said that the study findings lay the groundwork for further investigation into the relationship between sleep and psychiatric illnesses.
"This is the first set of experiments that demonstrate that even healthy people's brains mimic certain pathological psychiatric patterns when deprived of sleep. Before, it was difficult to separate out the effect of sleep versus the disease itself. Now we're closer to being able to look into whether the person has a psychiatric disease or a sleep disorder," he said.
The study is published in the Oct. 22 issue of the journal Current Biology.