People who sleep poorly at night tend to be more forgetful than people who sleep soundly. A good night's sleep is essential for memory consolidation. Although people vary in their need for sleep, six hours seems to be the minimum requirement to ensure that you are alert enough during the day to maintain optimal memory.

A 2000 Harvard study suggests that sleep improves skill learning. The skill, in this case, was performance on a visual discrimination task entailing rapid recognition of a subtle change in a visual pattern. The researchers found that college students who slept at least six hours performed better on the day following the initial learning than those who slept less than six hours. Students who slept eight hours did the best of all.

We believe that sleep benefits memory by enabling the brain to "replay" information that was encountered earlier. Evidence comes from imaging research in which researchers studied brain activity during memory acquisition and during a subsequent sleep phase. The scientists found that the neural pathways that were active during the learning period were reactivated during sleep. We believe that this is memory consolidation at work—that reactivation strengthens the neural pathways that hold the new information.

Sleep may also indirectly benefit memory by decreasing levels of stress hormones. As I mentioned earlier, stress hormones can interfere with memory by damaging the hippocampus. Stress hormones decline during the first few hours of sleep. Experts think that this decline helps the hippocampus operate at peak performance as it goes about its task of consolidating memories. J9_

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