Brain Rules for Aging Well: 10 Principles for Staying Vital, Happy, and Sharp

by John Medina

SUMMARY For clear thinking, get enough (not too much) sleep • Scientists don’t actually know how much sleep you need per night. Nor do we fully understand why you need to sleep. • The sleep cycle is born of a constant tension between hormones and brain regions vying to keep you awake, and hormones and brain regions trying to make you go to sleep. This is called opponent-process theory. • Sleep, we are finding, doesn’t have as much to do with energy restoration as it does with processing memories and flushing out toxins in the brain. • As you grow older, your sleep cycle becomes more fragmented, particularly the part of the cycle during which toxins are flushed out of the brain. • Accruing good sleep habits by middle age (a stable sleep routine; no caffeine, alcohol, or nicotine six hours prior to going to sleep) is the best way to avoid sleep-related cognitive decline in old age.