Different things happening in the brain during nonREM and during wakefulness and REM sleep.
The brain wave activity slows down during nonREM sleep. The signals become big and slow waves, like gentle ocean waves. This is when your body rests and repairs itself. You’re not dreaming much here.
When you’re awake, your brain is very active. It sends lots of fast signals because you’re thinking, moving, and paying attention. In REM sleep, your brain looks almost as busy as when you’re awake! The signals are fast and mixed up.
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