How does the amount of time in REM sleep in the beginning of the night, compare to the amount by the

end of the night?

ought that sleep was a passive state, a time when a person's brain and body shut down for the night to rest and recover. But now, researchers know that sleep is a highly active time, a period during which the brain and some physiological processes may be hard at work.

For example, some hormones involved in growth in children, cell repair or digestion are boosted during sleep. Brain pathways involved in learning and memory also increase, according to the National Institutes of Health (NIH).

In fact, the brain is sometimes more active when a person is asleep than when he or she is awake, according to Harvard Medical School. But sleep can also slow down many other physiological processes, from heart rate and breathing to body temperature and blood pressure.