How Our Brain Chemicals Synchronize During Sleep

What is it about?

Neuromodulators are chemicals in the brain that help control brain states, such as being awake or asleep. Traditionally, scientists believed that certain neuromodulators—like norepinephrine and serotonin—are released a lot when we are awake and much less during sleep. Recent research has shown that during non-REM sleep, these brain chemicals are not simply “off,” but are released slowly and rhythmically—about once every 30 to 50 seconds—creating very slow brain waves. An important open question has been whether different neuromodulators follow this rhythm together or act independently during sleep. In this study, we used advanced recording techniques to measure the release of norepinephrine, serotonin, and acetylcholine in two brain areas across sleep and wake states. We found that during non-REM sleep, these chemicals rise and fall together in a synchronized pattern. This coordination becomes stronger just before the brain wakes up. When we chemically blocked either the serotonin or norepinephrine system, the rhythmic release of the other neuromodulators disappeared. Likewise, when we artificially activated serotonin or norepinephrine neurons during non-REM sleep, it triggered the release of the other brain chemicals even without waking the animal. Overall, our findings show that the brain carefully coordinates the rhythmic release of multiple neuromodulators during sleep.

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Photo by Guilherme Coelho on Unsplash

Photo by Guilherme Coelho on Unsplash

Why is it important?

Our findings reveal a previously unknown way that different brain chemical systems work together during sleep. This teamwork may help the brain carefully control sleep and support important brain activities that happen while we sleep.