SAN DIEGO — Quantity, not quality, of sleep may determine how well older people’s brains function the next day, research reported February 21 at the annual meeting of the American Association for the Advancement of Science suggests. For youngsters, though, quality may be more important. The study shows that sleep affects young and old brains differently, and may ultimately lead to new ways to offset age-related cognitive decline.
The link between sleep and learning has been well-established, comments Matthew Walker of the University of California, Berkeley. “It’s critical to sleep before learning. Sleep almost prepares the brain like a dry sponge to soak up new information.”
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Contrary to common beliefs, older adults don’t sleep substantially less than younger adults. From age 35 to 85, people really lose only about an hour of nightly sleep, psychologist Sean Drummond of the University of California, San Diego said at the meeting. Rather, the thing that changes is something called sleep efficiency — a measure of the portion of time spent tossing, turning or lying awake in bed. “The biggest, most common, most robust change is that we spend more time awake in the middle of the night,” Drummond said.
In the new study, 33 adults with a mean age of 67 and 29 adults with a mean age of 27 slept in a lab while Drummond and his colleagues measured the duration and quality of their sleep. The next day, the researchers tested participants’ brain activity and performance on a learning and memory task.
Older adults who had slept for more total time the previous night were able to more accurately remember a list of random nouns than older adults who had slept fewer hours. What’s more, regions of the brain important for learning and memory showed higher activation in fMRI experiments in older adults who had slept more hours.
Sleep quality seemed to have no effect on performance, Drummond said. “For older adults, the absolute minutes of sleep they got last night has a significant influence on performance today,” he said.
On the other hand, in younger folks, the quality of sleep, and not the total amount, affected memory the next day, Drummond found. Young adults who slept in consolidated chunks performed better and had higher brain activity in certain regions than those who woke up frequently during the night, regardless of total minutes slept.
“Sleep last night does impact performance and brain function today, and it does so differently depending on whether you’re in your mid-20s versus your mid-60s,” he said. “Older adults need to get a certain amount of sleep. Young adults need to get that sleep in a consolidated chunk.”
The good news, Drummond said, is that disrupted sleep among the elderly is not harmful in and of itself. Rather, it’s the actual minutes of sleep that need to be watched. Tuning sleep quantity may be a way to prevent common cognitive decline that happens as people age, he said.