Word: braine
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...still hypothetical, but Tononi thinks he has evidence to back it up. "In slow-wave activity, all the neurons fire for half a second," he explains. "Then they're totally silent for half a second." For complex bioelectrical reasons, that turns out to be a perfect way for the brain to lower the strength of the connections between its neurons. Intermittent firing makes the connections leaner and more efficient and may even allow the weakest ones to drop out, clearing the mind so that it can learn something new in the morning...
Perhaps the brain just needs to restore itself. "We've all had the experience of going to bed with a problem, getting a good night's sleep and waking up in the morning, and there's a solution," says Dr. Gregory Belenky, who recently retired as head of sleep research at the Walter Reed Army Institute of Research in Silver Spring, Md., and is now at Washington State University at Spokane. But instead of thinking that extra information processing is going on during sleep, he says it makes as much sense to suggest that depleted circuits are just being rejuvenated...
...brain, like the rest of the body, runs on glucose, Belenky explains. Using computerized scanners that provide images in real time, he and his colleagues have shown that the brain's ability to use glucose drops off dramatically after being awake 24 hours, indicating a decrease in brain activity--despite the fact that there's still plenty of glucose available. The biggest drops occur in exactly those areas of the cortex that anticipate and integrate emotion and reason. After 24 hours, however, the drop-off stabilizes. "But performance doesn't level off," Belenky notes. "It continues to tank...
...addition to refueling the brain, sleep seems to detoxify it. Animals with a high metabolic rate, like field mice and bats, use a lot of calories and generate a lot of destructive molecules called free radicals. "The brain is particularly susceptible to this because neurons, by and large, don't regenerate," says Jerome Siegel, a neuroscientist at UCLA and the Veterans Affairs Medical Center in Los Angeles. Maybe sleep provides necessary downtime so that the brain can deal with all those free radicals...
Some of the most provocative sleep research doesn't have anything to do with the brain at all. A few years after researchers isolated a natural hormone they called leptin, which tells the brain that the body has enough fatty tissue, Eve Van Cauter and her colleagues at the University of Chicago began to wonder whether sleep deprivation has any effect on the amount of leptin in the blood. They soon discovered that after just a couple of days in which 12 male volunteers were allowed to get only four hours of sleep a night, their leptin levels fell sharply...