When You Space Out, Parts of Your Brain go to Sleep

Midday drowsiness might mean you’re already drifting off

Jason Stang/Corbis

If you have ever found yourself spacing out when you are tired, it’s because parts of your brain are going to sleep. A newly-discovered brain circuit triggers pockets of the brain to go to sleep while the rest of it keeps powering through the day, according to a study published this week in the journal eLife. These results could help scientists develop better sleep aids.

For many people, sleep feels like an all-or-nothing situation: Either you are awake or you are asleep. But as it turns out, your brain doesn't just switch off when you go to bed.

When you are asleep, in a coma, or under anaesthesia, a part of the brain called the thalamic reticular nucleus (TRN) starts sending slow brain waves to the brain’s cortex. These “slow waves” are the same signals that trigger deep sleep and may help the brain solidify memories. When slow waves are activated while you’re awake, they still send parts of your brain to sleep, making you feel drowsy, Andrew LeSane writes for Mental Floss.

“When you induce these slow waves across the cortex, animals start to behaviorally act like they’re drowsy. They’ll stop moving around, their muscle tone will go down,” study author Laura D. Lewis says in a statement. “I’m inclined to think that happens because the brain begins to transition into sleep, and some local brain regions become drowsy even if you force yourself to stay awake.”

To test whether the TRN could cause daytime drowsiness, Lewis and her group tried stimulating the region in mice to see whether the rodents would get sleepy. When they triggered the TRN, the mice’s brains produced slow waves, making the mice spacy and drowsy. Not only does this seem to be the reason you might reach for that 3 P.M. coffee, but it suggests that the TRN can send people into a deep, dreamless sleep much like anaesthesia, Samantha Olson writes for Medical Daily.

“The TRN is almost certainly a site of action of many anesthetic drugs, given that a large classes of them act at these synapses and produce slow waves as one of their characteristic features,” study co-author Emery Brown says in a statement.

While anaesthetics are a critical part to many modern medical treatments, scientists still don’t completely understand why they work. But if scientists are able to use the TRN to send people to sleep like their mice, it could help make anaesthetics and sleep drugs that better mimic natural sleep patterns and have fewer side effects.

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