Scientists report that they have found a master switching mechanism for sleep.
When the switch - a tiny clump of cells found deep in the brain - is turned on, all brain cells involved in arousal and awareness are shut down. When the switch is turned off, the brain wakes up.
Most people have experienced the switch, said Dr. Clifford Saper, chief of neurology and neuroscience at Beth Israel Hospital in Boston, who led the research.
You are drowsy. The room is hot, the lecture is boring and you cannot keep your eyes open. The switch turns on, he said, and you are out.
It is not this mechanism, however, that makes people drowsy and starts them on the somnolent slide. That, said Saper, is another mechanism, yet to be discovered, a kind of dimmer switch. The newly discovered clump of cells turns out the lights entirely.
The new finding, described in today’s issue of Science magazine, was demonstrated in rats, but the researchers said it almost certainly applies to humans, too, because the brain circuits that control sleep are highly similar in all mammals.
The work looks “very interesting,” said Dr. Peter Reiner, an associate professor of neuroscience at the University of British Columbia in Vancouver. “This seems to be a master switch. If we can control it, it opens the door to novel ways of modifying sleep and waking states.”
In practical terms, the finding might lead to more efficient medications to treat insomnia and somnolence, Reiner said.
But it remains to be seen how the switch fits into the whole pattern of sleep, which is a complicated state, said Dr. Adrian Morrison, a sleep researcher at the University of Pennsylvania. “What they found,” he said, “is an important node in a larger system.”
Researchers have known that there must be brain cells, or neurons, that turn on only at the onset of sleep. But these cells are not marked with signposts in the brain, Morrison said, and so no one knew where they were or how they were connected to the billions of cells that function when the brain is awake.
Moreover, although there are many small clumps of specialized cells in the brain stem and the forebrain that help orchestrate circadian rhythms - the daily cycles of wakefulness and sleep - it has been a mystery how these cell groups connect to one another, Saper said.