When you're sleep deprived, cognition is one of the first functions to decline. Shortchange yourself on sleep by staying up late, continue this night after night, and you ultimately shortchange your memory. And if the problem is not resolved, your memory -- and your brain -- will not be functioning in the best way possible.
In this excerpt from our Johns Hopkins Memory Bulletin, neurologists Marilyn Albert, Ph.D. and Guy McKann, M.D. answer questions about sleep and how it affects the brain and memory.
Q. How much sleep does an adult need each night?
A. As people get older, a decrease begins in both the total time sleeping and the amount of time spent in the stage of sleep associated with dreaming. A newborn sleeps 16 hours per day. In contrast, the baby's 30-year-old mother sleeps six hours per day (if she's lucky), and only one quarter of this time, or two hours, is occupied by the deepest stage of sleep.
Starting in middle age (between 45 and 60), not only does the amount of sleep per night start to decrease, but also the character of sleep changes. People at these ages spend less time in the stage of sleep associated with dreaming and more time in the lighter stages.
As people get older, they are more likely to shift the time when they sleep, some going to bed and to sleep earlier and waking up earlier. Others are the opposite, staying up late into the night and sleeping much of the day. When people are in their 80s, these changes are even more pronounced. Their total time asleep per day may be only six or seven hours, including time spent in daytime naps. Even though a person may take several naps a day, the total time sleeping in naps is rarely over an hour. The idea that older individuals should sleep soundly for eight to 10 hours is clearly wrong.
As a rule of thumb, one hour of sleep is required for two hours of being awake. As we get older, that ratio becomes closer to 45 minutes of sleep to each two hours awake. In other words, throughout the day you gradually accumulate a "sleep debt." By the end of a 16-hour day, a younger person owes the "sleep bank" eight hours. In contrast, an older person has a sleep debt of only about six hours. By the end of a week, you may have accumulated a sleep debt of eight to 10 hours.
Q. What are the effects of sleep deprivation?
A. If you don't allot enough time for sleep, you become sleep deprived. Besides being sleepy during the daytime, sleep-deprived people often have problems with their thinking. They are slower to learn new things, they may have problems with memory, and their ability to make judgments may be faulty, enough so that they may think they are really starting to "lose it" when the problem is really not enough sleep.
Elderly people do not recover from sleep deprivation as quickly as younger people. In experimental situations where people are kept awake for 24 hours, those in their 70s take at least a day longer to recover from their subsequent daytime sleepiness than younger people. Gender may also make a difference in the time it takes to recover from sleep deprivation; women seem to be able to recover faster than men.
