By Steve Dent / Source: Engadget

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Have you ever spaced out in the middle of a conversation without dozing off completely? MIT scientists now have a better idea why: only part of your brain is sleeping while the rest stays awake. Neuroscientists always suspected that, but the MIT team proved it in mice by using “optogenetics” to stimulate a part of the brain associated with sleep. They showed that the “thalamic reticular nucleus” (TRN) not only triggers slow sleep waves across the brain, but controls individual regions as well. The research could lead to safer anesthetic techniques and improved drugs for insomniacs.

Optogenetics lets scientists modify mouse brains with algae DNA, making them light-sensitive. They can then hit targeted parts of the brain with lasers and observe the resulting behavior. The MIT team strongly stimulated the TRN (which wraps the thalamus), generating slow waves in the entire cortex (outer brain layer) and putting the mice to sleep. However, when they stimulated the TRN with weaker beams, they produced slow waves in just a small part of the cortex, making the animals “behaviorally act like they’re drowsy,” said research affiliate Laura Lewis. “(We) 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.”

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While science already theorized such behaviour, “the strength of this paper is that it’s the first to use optogenetics to try to dissect the role of part of the (TRN) circuitry in generating slow waves in the cortex,” according to independent researcher Mark Opp. That could help neuroscientists figure out ways to trigger it to produce different types of sleep in subjects, especially more restful deep, non-REM sleep. It could also result in anesthesia drugs that produce more of a sleep-like state so they don’t completely knock out patients — helping eliminate those horrible side effects.

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