Everyone knows that a bad sleep equals a bad mood. Now a study that probes the inner workings of the brain tells us why.
U.S. scientists recently found that sleep deprivation triggers activity in parts of the brain responsible for emotions and rationality.
“People who are sleep-deprived will react more emotionally. Now we have a neural basis for this,” said lead author Dr. Matthew Walker, director of the Sleep and Neuroimaging Laboratory at the University of California, Berkeley.
Results of his study were published in this week's issue of the scientific journal Current Biology.
The study suggests that too little sleep could even be a catalyst for psychiatric illness. This finding has particular significance at a time when sleep deficits are said to have reached epidemic proportions.
For the study, 26 healthy young adults were divided into two groups. One group stayed awake all day, all night and all the next day (35 hours), and the other group got a normal sleep during the night. Subjects then underwent brain scans while they looked at 100 images that were increasingly negative, starting with neutral photos of spoons or baskets and moving to disturbing pictures of mutilated bodies and children with tumours.
Brain activity while viewing the stressful images was dramatically different between those who had slept and those who had not. The difference occurred in the amygdala, a part of the brain responsible for emotional responses.
“In those who are sleep-deprived, the amygdala goes into a hyperdrive situation so that it is approximately 60 per cent more reactive than [in] those who got a good night's sleep,” said Dr. Walker, who published the research with colleagues from Harvard medical school.
Lack of sleep also inhibits the activity of the medial-prefrontal cortex of the brain, which normally puts the brakes on the amygdala, he said.
“This part of the brain tries to quiet down our emotional reactions. When we get a good night's sleep, that is nice and intact, but when that connection is severed, the emotional brain is allowed to run amok.”
Bottom line: You're wired to be cranky when you're tired.
Though this was a small study, it may have large implications in the mental health realm. It showed that depriving healthy people of sleep causes patterns in the brain similar to those seen in cases of depression and post-traumatic stress disorder. This suggests that a lack of shut-eye can actually cause psychiatric illness.
“Almost all psychiatric conditions are associated with abnormality of sleep, but it was always a chicken-and-egg scenario,” said Dr. Walker. “Does the lack of sleep cause the psychiatric condition or does the psychiatric condition cause the lack of sleep? This study makes us consider more strongly the role of sleep in contributing to psychiatric disorders.”
Dr. Jeffrey Lipsitz, medical director of the Sleep Disorders Centre of Metropolitan Toronto, said the study helps explain why people who are sleep-deprived may appear to be “on a short fuse.”
“I am not at all surprised by the observation, though perhaps by the magnitude of the effect,” he said.
Most worrisome is when this emotional, hair-trigger response occurs in people who have positions of power or who work in safety-critical occupations. Disasters such as the Exxon Valdez oil spill and the Chernobyl nuclear power plant explosion have been blamed on lack of sleep in those in charge.“Road crashes, errors and inefficiencies on the job, workplace accidents, disability claims, absenteeism, and high staff turnover are just some of the very costly consequences that have been attributed to poor quality or inadequate sleep,” Dr. Walker said.
He added that sleep deprivation – and its intrinsic irrationality – could have deadly consequences in a military field of action.
Dr. Lipsitz calls lack of sleep “a public health epidemic.” One in seven Canadians is an insomniac, and almost half of our population admits to voluntarily cutting down on sleep, according to Statistics Canada.
Dr. Lipsitz suggests that a healthy adult needs 81/4 to 81/2 hours of sleep a night. “On average, nobody is getting that.”
So, are we more emotionally volatile than our grandparents were? We may well be.
“Over the last 100 years, there has been a trending decrease in sleep,” noted Dr. Walker. “What we are led to believe in society is that people are increasingly more irrational. So there are two diverging lines.” His recent study provides a biological clue linking the two phenomena.
Dr. Walker's team is planning further studies in more “real life” scenarios, such as what happens in the brain when you sleep for only five hours a night for a whole week.
Special to The Globe and Mail
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