For psychiatrists, having too much or too little sleep can be a sign of mood disorders, such as depression. As a rule, doctors say sleep problems make almost every illness worse.
Sleep disturbance is also one of the symptoms on the checklists for diagnosis of both depression and bipolar disorder in the Diagnostic and Statistical Manual of Mental Disorders.
Scientists know sleep is important -- animals do it daily -- but it's still an enigma.
During the first phase, the brain is in deep, slow-wave sleep, with alternating periods of rapid-eye movement (REM) or dream sleep, which is marked by faster brain waves. As the night progresses, REM sleep becomes more frequent.
During the day the neurons in the cortex, or cognitive part of the brain, are active, but during sleep the neurons quiet down.
Using brain imaging, the San Diego researchers found a small area of the cerebral cortex in the front of the brain -- the anterior cingulate cortex -- which was overactive in depressed patients. But after those patients were robbed of sleep, those levels quieted.
Interestingly, antidepressants such as tricyclics and SSRI's block REM sleep. And families with a rare genetic defect that extends REM sleep into earlier in the sleep cycle are more prone to depression, according to Sejnowski.
Scientists see the same effect after sleep deprivation in some healthy individuals. The occasional all-nighter, as all college students know, can sometimes cause a temporary state akin to euphoria.
Emily, a 21-year-old senior at Syracuse University who does not suffer from depression, lost an entire night's sleep last summer.
"I couldn't fall asleep for the life of me," she said. "By the time it got to be three in the morning, I just wasn't tired at all. I just laid in bed until about five."
But instead of feeling shattered and depressed at dawn, Emily, a journalism and political science major, said her mood began to lift and she put on her running shoes.
"It was one of the best runs of my life," she said. "I felt like I had a full night's sleep. I ran two extra miles than I normally do around the campus. I went through neighborhoods multiple times because I just didn't feel tired enough to stop."
"I was more numb or immune to the feeling of pain," said Emily. "This time, it took me longer to reach that point of exhaustion."
In studies, she implanted a pacemaker-like device in the chest with wires that deliver electrical stimulation to a part of the brain that is close to the anterior cingulate cortex, disrupting neural activity.
Unlike electroconvulsive shock treatment (ECT), the electrical current is gentler and does not cause an epileptic fit.
The patients in Mayberg's study are treatment resistant, even with ECT, and struggled with major depressive episodes for at least one year or more.
"These people are very, very sick," she said. "They are stuck and can't get out of it. They are off the map."
The procedure "allows the brain to go back to normal," said Mayberg, a professor of psychiatry and neurology. "While we get an immediate behavioral change in the operating room, the antidepressant effects require several months to become apparent, and continued stimulation is required to maintain it longterm."