Experience tells us that sleepless nights can lead to overwrought emotions. Now scientists have uncovered some of the first evidence of how this occurs. Their imaging studies show that lack of sleep can lead to greater activation of the brain’s emotional centers and disrupt the brain circuits that tame emotional responses.
Adequate sleep is essential to good health, yet many Americans don’t get enough. About 75% of adults have symptoms of sleep problems at least a few nights each week, according to the National Sleep Foundation. Countless studies have shown that lack of sleep can interfere with a range of biological processes, including learning and memory and your ability to fight disease. However, research into the physical connections between sleep and emotions has been sparse.
Dr. Matthew Walker and his colleagues at the University of California, Berkeley, and Harvard Medical School set out to examine how sleep loss affects activation of the brain’s amygdala. This primitive brain region triggers emotional responses to potentially threatening, nonverbal cues. The study, published in the October 22, 2007, issue of Current Biology, was funded by NIH’s National Institute of Neurological Disorders and Stroke (NINDS), National Institute of Mental Health (NIMH) and National Center for Research Resources (NCRR), along with the American Academy of Sleep Medicine.
The scientists assigned 26 healthy people to either a normal sleep group or a sleep-deprived group, who were kept awake for about 35 hours straight—about how long you’d be up if you stayed awake all night and into the next afternoon without naps. Functional MRI scans then measured participants’ brain activity while they viewed 100 images. The initial images were emotionally neutral. They later became increasingly unpleasant and disturbing—for example, showing a dirty toilet bowl, a burn victim, a dying patient or mutilated bodies.
Both groups had greater amygdala activation in response to more negative pictures. The intensity and volume of activation, however, was significantly amplified in the sleep-deprived group. “The size of the increase truly surprised us,” Walker said. “The emotional centers of the brain were over 60% more reactive under conditions of sleep deprivation than in subjects who had obtained a normal night of sleep.”
Lack of sleep also seemed to have another effect on the brain’s emotional controls. The amygdalae in the sleep-deprived group appeared to be more strongly connected to the brain’s primitive, impulsive regions and less connected to the more sophisticated and rational prefrontal lobe, which normally keeps emotions and behaviors in check. Malfunctioning brain circuits linking the amygdala to the prefrontal lobe have been associated with depressive symptoms.
“This study demonstrates the dangers of not sleeping enough. Sleep deprivation fractures the brain mechanisms that regulate key aspects of our mental health,” Walker said. “Sleep appears to restore our emotional brain circuits, and in doing so prepares us for the next day’s challenges and social interactions.”