Sleep doesn’t help old folks remember

WASHINGTON — For young people, snoozing means big gains in memory. But in older folks some of sleep’s memory-boosting abilities are erased, a new study finds.

Sleep has been shown in a wide variety of studies to increase people’s ability to recall words and objects and to improve physical skills. But that boost may be available only to the young, Lauri Kurdziel and Rebecca Spencer of the University of Massachusetts Amherst reported November 13 at the Society for Neuroscience annual meeting.

Previously, the researchers had shown that a night of sleep improved young people’s ability to learn a series of button presses similar to playing a piano. Adults in the over-50 age group didn’t get a bump in performance from sleeping. But that difference may have been due to older folks’ slower reaction times.

A new study, though, suggests that it’s sleep’s memory benefits that are reduced with age. Kurdziel and Spencer had a group of 18- to 30-year-olds and a group of 50- to 80-year-olds learn a sequence of colored doors that would lead them through 10 virtual rooms. The researchers then tested the participants’ memories 12 hours later, either in the evening of the same day or after a night of sleep.

Young people who took the test after being awake all day made about 10 errors on average, but a night of sleep nearly halved the number of mistakes. In the over-50 group, a night of sleep didn’t help. The people made just as many errors after sleeping all night as they did if they took the test after being awake for 12 hours.

The reason older people have trouble learning new tricks may be due to fragmented sleep patterns, said Kurdziel. Older people sometimes wake up more in the night (often to go to the bathroom), but also as people age, their sleep cycles get shorter. Although older and younger people get the same amount of sleep overall, older people spend less time per cycle in each of sleep’s stages. Particularly important in this case may be that older people spend less time in sleep stage 2, in which the day’s events are played back and committed to memory. It could be that older people just don’t have enough time to replay and remember the entire sequence of door choices, Kurdziel said.

The study suggests that researchers need to identify the reason sleep cycles speed up and sleep becomes more fragmented with age, said Barbara Sahakian, a neuroscientist and clinical psychologist at the University of Cambridge in England. “It’s difficult to do much about it at this stage without knowing what’s driving it.”