These slumbering people are recharging their bodies, sweetly dreaming to prepare for a new day. But their brains are buzzing with activity. While we sleep, the part of the brain responsible for memory has a lot of work to do. Researchers have found that during the dreaming phase of sleep, your brain saves procedural memories—how to do the tango, or how to play chess. There is also evidence that during the deepest phase of sleep, your long-term memories are being processed and stored in your brain. The most dramatic evidence of sleep's importance to memory is found in people with obstructive sleep apnea (OSA). Part of their brain can actually shrink away! OSA sufferers are sleep-deprived because a structural defect temporarily blocks their breathing, causing them to wake frequently and gasp for air throughout the night. Their mammillary bodies—globe-like structures in the brain which play a role in long-term memory—get smaller. In addition to memory impairment, those who sleep too little are more likely to be overweight, irritable, less alert or depressed.

So, how much sleep is enough? The National Sleep Foundation recommends that adults get 7 to 9 hours of sleep per night, although individuals have different needs within that range. The most serious health effects from sleep loss occur in those regularly getting less than 5.5 hours a night. To give yourself the best chance at a good night's sleep, swear off alcohol and caffeine too close to bedtime. Keep a regular sleep schedule, even on the weekends. Ease into sleep with soothing, relaxing activities for an hour or so before bedtime, and sleep in a room that is dark, quiet, cool and comfortable. If you feel chronically tired and unfocused no matter how hard you try to sleep, ask your doctor if you might have sleep apnea—a serious condition, more common in obese people, that requires medical intervention.

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