Sleep Deprivation Leads to Emotional Instability Even in Healthy Subjects

October 25, 2007 — New research sheds important light on the link between sleep deprivation and psychiatric illness. A study appearing in the October 22 issue of Current Biology shows that parts of the brain governing emotional responses were much more active in people who had skipped a night's sleep and were exposed to disturbing images than in a control group of individuals exposed to the same pictures.
"The study provides a new foundation of evidence on which to consider more seriously that sleep may play a significant role in regulating our emotional stability," said Mathew Walker, director of the University of California, Berkeley's Sleep and Neuroimaging Laboratory, and senior author of the study.
"This is the first set of experiments that demonstrate that even healthy people's brains mimic certain pathological psychiatric patterns when deprived of sleep."
Sleep-Deprived Brains More Reactive
Dr. Walker and his colleagues enrolled 26 healthy undergraduates aged 18 to 30 years and separated them into 2 groups with equal numbers of males and females. One group stayed awake for about 35 hours (1 day, 1 night, and the following day) while the control group stayed awake on both days but slept normally at home during the night. At the end of the second day, both groups were shown 100 images that ranged from the emotionally neutral to the highly disturbing (ie, pictures of mutilated bodies and children with tumors) while undergoing brain scanning with functional magnetic resonance imaging (fMRI).
When the researchers quantified and compared brain activity in the amygdala, the area of the brain that oversees emotional reactions, they found significant differences in the brains of the sleep-deprived group when they were exposed to the negative pictures. "Rather than the brain being dulled or suppressed in its activity when you're sleep deprived, we found that the deep emotional centers of the brain were approximately 60% more reactive when you're sleep deprived," Dr. Walker told Medscape Psychiatry.
The amygdala serves to alert the body to protect itself in times of danger, according to background information supplied by UC Berkeley. In the setting of sleep deprivation, the amygdala goes into overdrive in response to emotional images — for example, shutting down the prefrontal cortex, the area of the brain that governs logical reasoning. Instead, it activates the locus coeruleus, which releases noradrenaline to ward off imminent threats to survival, a potentially volatile mix, they note.
Chicken or Egg?
The study provides useful insights into the relationship between sleep disruption and mood and other psychiatric disorders, said Dr. Walker. Almost all psychiatric conditions have some sleep abnormalities, he explains. "In fact, it's difficult to find a psychiatric disorder, particularly ones involving emotion, that don't have some kind of sleep impairment." The issue that has remained unresolved, however, is the exact relationship between sleep and psychiatric illness: does a psychiatric disorder cause sleep impairment, or does a sleep problem cause a psychiatric disorder?
In the past, most people assumed that sleep disorders were an offshoot of psychiatric problems, but this study casts doubt on that assumption, he said. It shows that emotional reactions of healthy but sleep-deprived people are similar to those seen in psychiatric disorders. "The patterns of brain activity that you see in those healthy people who have had a lack of sleep are not dissimilar to the patterns of brain activity that you see in people suffering things like depression and [posttraumatic stress disorder]," said Dr. Walker.
Although the difference in emotional brain responses between the 2 groups in the study averaged 60%, it ranged from as low as 40% to as high as 80%. One of the next steps for researchers, Dr. Walker said, is to determine whether women are more likely to have the greater emotional brain reaction when they're sleep deprived. "That's something we will be looking into," said Dr. Walker.
Researchers already believe that there's a closer relationship between sleep disturbance and depression among women than among men. If that is the case, "it suggests that what we should find in our results is that the females should be responding more abnormality than the males, but we don't know that yet."
What About the Real World?
Another question that remains unanswered is whether the relationship between sleep deprivation and psychiatric disorders exists not just inside the controlled environment of a sleep laboratory but also "in the real world," where people may not be totally sleep deprived but may regularly get only a few hours of sleep a night. "We don't know yet whether there would be the same amplified emotional brain response if we were to put people on a 5-hour sleep schedule for a week, so they accumulate approximately the same amount of sleep deprivation, and then perform the same experiment," he said.
Another element of the real world is shift work. There is anecdotal evidence that people who work overnight shifts might be more emotionally unstable than other workers, said Dr. Walker. "In terms of their mental health, they just don't seem to be functioning very well. I think [with this study], we're starting to see some of the reasons [for this]."
The authors report no relevant financial relationships. The research was supported in part by grants from the National Institutes of Health and the American Academy of Sleep Medicine.
Current Biology 2007;17:95-97.