The first evidence that sleep deprivation has a neurological link to anxiety, depression and other psychiatric disorders, has been published in the October edition of the journal Current Biology.
The need for sleep is best illustrated by what happens to us when we are deprived of it. A good night’s sleep regulates mood and helps us to prepare for the following day’s challenges, but anything over 24 hours of sleep deprivation leads to impaired reflexes, difficulties in problem solving and irritation. If sleep is deprived over 48 hours, confusion, misperceptions and task requiring attention become seriously impaired.
Results from the first neural investigation into what happens to the areas of the brain associated with emotions when deprived of sleep, have revealed some interesting issues. Assistant professor Matthew Walker, director of UC Berkeley’s Sleep and Neuroimaging Laboratory stated, "this is the first set of experiments that demonstrate that even healthy people’s brains mimic certain pathological psychiatric symptoms when deprived of sleep".
The study focused on an area of the brain called the amygdala. The amygdala is about the size and shape of an almond and is known to have an important role in the regulation of emotions. Using functioning Magnetic Resonance Imaging (fMRI) the research team found the amygdala became hyperactive in volunteers who had stayed awake for 35 hours and who were then exposed to a series of disturbing visual images. Those who were not sleep deprived showed normal neural activity when shown the same images.
Walker described the effects as, "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".
One of the main functions of the amygdala is to prepare the body to protect itself in times of perceived danger. On sensing danger, or some emotional threat, the amygdala reacts and sends messages to an area of the brain known as the prefrontal cortex. The prefrontal cortex assesses the situation and sends the message to the brain either to react or switch off the fight-or-flight response.
However, in the case of people who have been sleep deprived, the relationship between the amygdala and the prefrontal cortex is bypassed. The amygdala in the no-sleep brain connects directly with the locus coeruleus and noradrenalin is released in order to prepare the body for action. "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.
During his experiments, Walker examined 26 people divided into two equal groups of men and women. The sleep deprived group stayed awake for two days and one night, whilst the control group slept normally. Brain scanning was undertaken at the end of the second day, during which 100 images ranging from neutral to very negative (e.g. mutilated bodies) were shown.
Sleep disorders are commonplace in nearly all psychiatric disorders. Walker states, "we’re closer to being able to look into whether the person has a psychiatric disease or a sleep disorder . . . all signs point to sleep doing something for emotional regulation and emotional processing".
Professor Walker now aims to turn his attention to the two phases of sleep that occur during the night: Rapid Eye Movement (REM) and Non-Rapid Eye Movement (NREM) in an attempt to discover their role, if any, in the process.
Yoo, S., Gujar, N., Hu, P., Jolesz, F.A., Walker, M.P. (2007) The human emotional brain without sleep a prefrontal amygdala disconnect. Current Biology 17: 877-878