Why do our brains need sleep instead of staying active all night?

Sleep is essential because the brain uses it for memory consolidation and for maintaining healthy function across many networks. During sleep, the brain reorganizes information from the day and supports processes linked to learning and emotional regulation. Lack of sleep makes the prefrontal cortex less effective, which hurts focus, impulse control, and judgment. Sleep research over the last century has made it clear that sleep is not wasted time; it is active maintenance for the brain.