There are time-of-day effects for alertness and performance that become starkly emphasized when we age. Adults after the age of sixty or so begin to show performance differences on a range of neuropsychological tests—memory, problem solving, spatial intelligence, reasoning, fine motor coordination, and athletic performance. Test them in the morning and they are normal; test them in the mid- to late afternoon and they show reduced performance, compared to forty- or fifty-year-olds (as we saw in Chapter 4, on the problem-solving brain). The differences become even more pronounced after age
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