The researchers conducted the following study to study the relationship between sleep and memory  They were tested for sleep and memory at age 21 and 75 respectively  The subjects were tested for word memory before falling asleep at night  The results showed that older people had about 25 percent worse word memory than younger people  During sleep, the researchers used electroencephalograms to detect sleep and brainwave activity in subjects, and older adults slept 75 percent less slow-wave sleep than younger people on average  The day after eight hours of sleep, the researchers again tested memory of previous words  The results showed that older people had a 55 percent worse score in word memory the next day than younger people
The quality of sleep depends on the length of slow-wave sleep and the length of fast-wave sleep
 As a result, researchers believe that shorter slow-wave sleep times are key to affecting memory in older adults