Maintenance time
Why Do We Sleep?
Sleep is when the body repairs itself and the brain files what happened.
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Step 1 of 5
Every animal does it, despite the danger.
Being unconscious for hours is enormously risky. That it evolved anyway, everywhere, means it must be doing something essential.
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Step 2 of 5
The brain sorts and stores memories.
During sleep the day's experiences are replayed and the ones worth keeping are moved into long-term storage. The rest fade.
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Step 3 of 5
The body does its repairs.
Growth hormone peaks during deep sleep. Muscle repair, tissue growth and immune work all happen most strongly while you are out.
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Step 4 of 5
The brain also gets washed out.
Channels between brain cells widen during sleep, letting fluid flush waste products away. It is a rinse cycle that only runs at night.
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Step 5 of 5
It runs in repeating cycles.
Roughly every 90 minutes you pass from light sleep to deep sleep to dreaming and back. Different repairs happen in different stages.
Going without sleep impairs you comparably to being drunk, and you get worse at noticing that you are impaired.
The short version
Sleep is when memories are sorted, the body repairs and the brain is flushed clean — too valuable to skip.
Try it yourself
Learn something new, then test yourself before bed and again after sleeping. Sleeping usually improves the score.
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