Understanding the Body’s Sleep Thermostat

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What makes people sleep? What causes people to wake?

One half of that answer involves circadian rhythm, the biological process that follows a 24-hour sleep-wake cycle. The other is the sleep homeostat, which scientists at the University of Oxford in Oxford, England, are studying.

“The sleep homeostat measures something—and we don’t know what that something is—that happens in our brains while we are awake, and when that something hits a certain ceiling, we go to sleep. The system is reset during sleep, and the cycle begins anew when we wake up,” says Gero Miesenböck, a neuroscientist at the University of Oxford, in a news release.

Researchers looked at a cluster of fruit fly brain cells that work as the homeostatic sleep switch, which turns on when the body needs rest and shuts off when its time to wake.

They discovered an ion channel, a type of molecular gateway that controls the electrical signals that allow brain cells to communicate. They named the ion channel Sandman, the release notes.

When they disrupted sleep by introducing dopamine, Sandman moved from the center of the cells to the outside, which caused the neurons to shut off and the flies to wake.

Researchers also discovered they could turn off the ion channel and the flies would remain asleep.

“In principle, this is a device that’s similar to the thermostat on the wall of your living room,” says Jeff Donlea, lead author of the study. “But instead of measuring temperature and turning on the heat when it is too cold, this device turns on sleep when your sleep need exceeds a set point.”

Miesenböck adds: “The billion-dollar question in all of this is: What is the equivalent of temperature in this system? In other words, what does the sleep homeostat measure? If we knew the answer, we’d be one giant step closer to unraveling the mystery of sleep.”

The research was published in Nature in August.