-- 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.
"Maybe we need to consider whether or not it's the sleep abornomality in some ways contributing to or causing the disorder," he says.
His reasoning, he says, is based on the fact that those studied didn't have psychiatric conditions.
"We imposed a sleep abnormality and the reaction from the emotional brain does not look dissimilar from certain psychiatric conditions," he says.
Carskadon, whose work has influenced changes in the start times of schools across the country, is particularly concerned about what this could mean for adolescents, who are often sleep-deprived and who are being diagnosed with depression in much greater numbers than in the past.
"What we don't know is whether early sleep deprivation then projects out to things like major depressive disorder or bipolar illness and whether we're really setting up our kids for these major problems as they grow up," she says.
She says college students need 8.4 hours of sleep a night, yet some data shows that even if they sleep 8 hours, performance decreases. Younger adolescents need at least 9 hours, she says.
Carskadon says young people don't get needed sleep because their internal clock changes after puberty and allows adolescents to stay up longer because it takes longer for sleepiness to build.
Orlando pediatrician Veenod Chulani, director of the division of adolescent medicine at Arnold Palmer Hospital for Children, says a lot of vital developmental processes in teenagers occur during sleep, yet most teens don't get enough.
"What the study does is provides a biological finding to support what we do see clinically," says Chulani, who studies sleep issues related to hypertension, diabetes and obesity.
Dinges, of Penn, says additional research is needed because this study doesn't indicate how the participants actually behaved.
'We don't know how well this data ties to the experiences that people have," he says. "It's one thing to process something that's more negative when you're tired. It's another thing to feel more negative when you're tired and the third thing is to behave more negatively when you're tired."
Walker says his study adds to the mounting evidence in brain science that sleep isn't a luxury but a biological necessity.
Sleep "resets the emotional barometer and prepares us for our next day's emotional challenges," he says." "To get the best quality out of the time you're awake, you actually need sleep."