How the brain controls sleep

Oct 20, 2015

Illustration by Jose-Luis Olivares/MIT

By Massachusetts Institute of Technology

Sleep is usually considered an all-or-nothing state: The brain is either entirely awake or entirely asleep. However, MIT neuroscientists have discovered a brain circuit that can trigger small regions of the brain to fall asleep or become less alert, while the rest of the brain remains awake.

This circuit originates in a brain structure known as the thalamic reticular nucleus (TRN), which relays signals to the thalamus and then the brain’s cortex, inducing pockets of the slow, oscillating brain waves characteristic of deep sleep. Slow oscillations also occur during coma and general anesthesia, and are associated with decreased arousal. With enough TRN activity, these waves can take over the entire brain.

The researchers believe the TRN may help the brain consolidate new memories by coordinating slow waves between different parts of the brain, allowing them to share information more easily.

“During sleep, maybe specific brain regions have slow waves at the same time because they need to exchange information with each other, whereas other ones don’t,” says Laura Lewis, a research affiliate in MIT’s Department of Brain and Cognitive Sciences and one of the lead authors of the new study, which appears in the journal eLife.

The TRN may also be responsible for what happens in the brain when sleep-deprived people experience brief sensations of “zoning out” while struggling to stay awake, the researchers say.


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