Sleeplessness agitates the brain

Sleep deprivation makes the brain groggy, but as waking hours mount nerve cells grow increasingly jumpy, a new study shows.

This amped-up state may explain why seizures and hallucinations can accompany an all-nighter. More generally, the results help clarify what goes wrong in a brain deprived of shut-eye.

“It’s an important finding,” says neuroscientist Christopher Colwell of UCLA. “Sleep deprivation is an area of huge interest because most of us do not get enough sleep.”

By subjecting six people to a night of sleep deprivation and measuring their brain responses, Marcello Massimini of the University of Milan and colleagues found that people’s brains become more reactive as hours awake accumulate.

To look for signs of altered brain function, the team delivered magnetic pulses to the participants’ skulls that kicked off an electrical response in the nerve cells (an effect like the noise made when a hammer strikes a bell). With electrodes on the scalp, the team measured the strength of this electrical response in the frontal cortex, a brain region that’s involved in making executive decisions.

After a night of sleep deprivation, participants’ electrical responses were stronger than they were the previous day, the scientists report online February 7 in Cerebral Cortex. This overreaction disappeared after a night’s sleep.

The results offer support for a theory of why people sleep: During waking hours, the brain accumulates connections between nerve cells as new things are learned. Sleep, the theory says, sweeps the brain of extraneous clutter, leaving behind only the most important connections.

Enhanced excitability in the brain may explain why sleep deprivation can trigger seizures, events marked by massive nerve cell excitation. When doctors want to induce seizures in patients in the clinic, one of the most effective ways is to keep a person awake all night.

The new results also have an intriguing link to depression. For some people, sleep deprivation can quickly reverse symptoms of depression, an effect that may be due to the brain’s boosted excitability, Massimini says. The team plans on studying people with depression to see if their brains show similar responses to sleep deprivation.