Med thumb light switch

While scientists know the purpose of our circadian rhythms and understand how an off-kilter internal clock can wreak havoc on people, they’ve long been baffled by the exact mechanism by which it functions. By studying the suprachiasmatic nucleus — the circadian control center — in the brains of fruit flies and mice, researchers at Northwestern University, however, believe they’ve discovered a switch that brings us in and out of sleep.

A properly functioning body clock adopts roughly the same 24-hour-cycle that dictates our alarm clocks and calendars, primarily because our circadian rhythms align with daily patterns of waning light and darkness. Problems arise when someone’s body clock falls out of sync, either because they have a circadian rhythm disorder or some lifestyle interference like shift-work throws off their schedule. In an effort to help people adapt to and stay on a 24-hour-cycle, chronobiologists have tried to pin down and flesh out the brain mechanisms responsible for running our sleep-wake system.

The Northwestern team, which published their findings this month in the journal Cell, pinpointed a suspected ancient sleep-wake “switch” in the brains of insects and rodents that’s triggered by increased levels of sodium and potassium. Here’s how lead study author Matthieu Flourakis laid out the complex discovery to Van Winkle’s:

“In our study, we show that our internal clock controls the activity of sodium and potassium channels. Higher sodium channel activity result in more sodium currents (more sodium getting into the neurons), this excites the neurons and in turn wakes up the animal. At night, sodium channel activity will be low (low sodium current, lower sodium getting into the cell), but potassium channel activity (more potassium currents) would be high. In this case, more potassium comes out of the cell, which silences (decreases the activity of the circadian neurons) and puts the animal to sleep.”

This could be big. Given that the biological clocks of mice and humans operate nearly identically, the same switch may very well control sleeping and waking in humans, too.

“What is remarkable,” Flourakis told Van Winkle’s via email, “is that this mechanism is conserved throughout evolution, as it is present in insects and mammals.”

The Northwestern team, however, isn’t the first to lay claim to discovering a circadian master switch. Earlier this year, Vanderbilt researchers uncovered a “reset button” in the mouse biological clock. They used a technique called optogenetics to stimulate neurons in the suprachiasmatic nucleus. By altering the neurons’ sensitivity to light, researchers found they could emulate day and night neuronal activity which, presumably, would let them artificially shift the body clock.

How do the discoveries differ, exactly?

“[Vanderbilt researchers] used light and optogenics to artificially stimulate the neurons," said Flourakis. "In our study, we demonstrate how our own internal clock naturally controls the neurons’ activity.”

No, the study doesn’t mean that one day you’ll be told to suck down Morton salt by morning and inhale bananas at night to keep your rhythms in check. But, the knowledge could eventually help scientists fix circadian rhythm disorders.