At bedtime, you shut down your computer, smartphone, and busy schedule—but for your brain, the workday’s just getting started. In fact, your brain remains highly active throughout your sleep so it can perform a host of functions that keep you humming through the day:
Cerebral spinal fluid is pumped more quickly throughout the brain while you sleep. It acts like a vacuum cleaner, whisking away waste products, such as molecular detritus that brain cells make and toxic proteins that can lead to dementia over time. So you wake up with, quite literally, a clean slate.
The brain restores information that wasn’t ingrained during the day—such as, say, the password you vowed to remember. Experts call this consolidation, and it’s important for protecting against further information loss as well as boosting your ability to learn while you’re awake. It can even enhance your language skills and hand-eye coordination.
That’s especially true for emotional ones: Your brain chooses and enhances the experiences that are most valuable to you—your child’s graduation speech, for example. What’s more, it downgrades memories that aren’t as important (like what was served at graduation dinner).
The brain replays the memories of your daily to-dos, and helps to reestablish the order in which those things occurred. This happens during the deepest stage of sleep.
In the deepest stage of sleep, stage 4, the part of your brain that’s responsible for relaying nerve impulses throughout the spinal cord sends a message to turn off motor neurons, causing temporary paralysis. Why? So you don’t find yourself trying to recreate the stories that are running through your mind when you’re asleep.