Cranky and irritable?
Your brain is trying to tell you something: It's sleepy.
You might have guessed it, but now researchers have real proof. The first neurological probe into the emotional brain without sleep has found evidence that sleep deprivation causes our emotions to go haywire, says a study from the University of California, Berkeley, and Harvard Medical School.
"Most people think when you're sleep-deprived what happens to the brain is that it becomes sleepy and less active," says Matthew Walker, the study's senior author who is an assistant professor of psychology at UC Berkeley and a former Harvard sleep researcher.
But Walker, who directs Berkeley's Sleep and Neuroimaging Laboratory, says the brain imaging study published online today in the journal Current Biology found the emotional centers of the brain to be "60% more reactive."
The study also suggests that lack of sleep elevates activity in the emotional centers of the brain most closely associated with psychiatric disorders such as depression and may help explain the link between the often disrupted sleep of those with such disorders.
Lack of sleep has been found to impair the physical and mental functions of the body, including the immune system, metabolism, learning and memory. A report released last year by the Institute of Medicine, which advises the federal government, found a relationship between sleep deprivation and increased risks of hypertension, diabetes, obesity, depression, heart attack and stroke.
Sleep researchers not associated with this study say this use of functional MRI is important because it provides a neurological basis for what has largely been anecdotal.
"It's been hard to document," says David Dinges, a sleep scientist at the University of Pennsylvania School of Medicine. "With imaging, we're beginning to understand how the brain changes when our lifestyles deprive us of sleep. Going without adequate sleep is very common in the world. It's important for us to identify what happens in the brain when we do that. It does change areas of the brain activity in a way that we are not properly able to manage our emotions."
Mary Carskadon, a professor of psychiatry and human behavior at Brown University who has studied adolescents and sleep deprivation, says the new study is compatible with findings from her sleep lab.
"This is first one I know of that's used imaging," she says. "It's been hard to see these interactions in real time, but functional MRI allows one to do that. It really does seem to point to this highlighting of the negative when you don't have sleep."
Walker's team of researchers studied 26 people ages 18 to 30, divided into two groups of equal numbers of men and women. The sleep-deprived group was awake 35 hours, while the other group slept normally at night and was awake by day.
Using the brain scans, the researchers showed the participants a series of images, beginning with neutral examples, such as a basket on a table, and becoming increasingly negative and disturbing, such as snakes and gory mutilations. The responses of both groups showed up as hot spots, but Walker says the sleep-deprived showed stronger responses because the prefrontal area of the brain that normally sends out inhibiting signals wasn't able to keep emotions in check, Walker says.
While the thinking about psychiatric disorders has been that the disorder caused the poor sleep, Walker says now, he's not so sure.