Sleep can improve memory

Three outliers were identified and removed; one high scoring subject assigned to the sleep and two lower scoring subjects assigned to no sleep. After removing outliers, 19 sleep subjects and 18 no- sleep subjects remained.

The number correct on the letter-number control task at initial testing was 6. The letter-number correct score on the second administration was 6. When the three outliers are included, the number correct for recall of the paired-associates was statistically greater for the sleep group 7.

The paired-associate test is one of the standard tests of declarative memory and has been previously used to study declarative memory and the effects of sleep on declarative memory in adults and children [3].

All subjects were evaluated at the same two times of day, approximately 9 AM and 9 PM, using standardized conditions. Performance on the paired-associate test was significantly affected by sleep in our adolescent sample. Correct performance on the letter-number working memory task LN requires that the letters and numbers presented to the subject must be encoded and then correctly manipulated.

The equal performance at both sessions and between groups on the LN supports the view that equal registration and encoding of the memoranda was comparable at both time points and between groups. Performance on the working memory control task did not change with the second session for either group, suggesting that the time of day had no effect on performance on the working memory control task.

Consequently, the observed difference in paired-associate performance, i. Memory consolidation has been reported to be affected by sleep [1] , [2] , [8] , [9]. Both REM and slow-wave sleep have been associated with improved memory [3] — [5]. Slow wave sleep particularly enhances declarative memory. Our results are consistent with Gais et al.

Naps improve declarative memory regardless of time of nap [16] and closely resembled memory improvement after an eight-hour night of sleep [17]. In reviewing the timing of sleep and circadian rhythms, Diekelmann et al. Voderholzer et al. The paired-associate test begins as a working memory task and after a period of time with consolidation becomes a declarative memory task. Correct performance on the letter-number test and the paired-associate tests are dependent upon encoding the memoranda.

A limitation of this study is that we did not test for encoding strength by immediate recall after the administration of the paired-associate test. The letter-number test requires attention and encoding. An element of immediate recall is to prove that the subject was attending. It is likely that if immediate recall following each presentation was obtained, higher accuracy rates would have been observed.

Recent studies have demonstrated that salience increases declarative memory performance [13] , [19]. Nevertheless, our data demonstrate that sleep improves memory consolidation even in conditions where encoding has not been reinforced. Neither time of day or sleep affected the performance on the letter-number test suggesting that the material was being learned and encoded. There is no evidence that memory consolidation depends on time of day independent of sleep.

The lack of interference during sleep has been considered as a possible cause of the beneficial effects of sleep on declarative memory, i. Our design tested subjects on non-school days, thus mitigating the effects of interference of memory consolidation during the day by learning competition and other demands of a normal school day. Gais et al. In a review of controversy regarding whether absence of interference accounts for memory improvement during sleep, Ellenbogen at al. Diekelmann et al.

Children have high amounts of slow wave sleep and sleep in general. Sleep has been shown to improve declarative and procedural memory in children and older age groups. Subjects were asked about their sleep and confirmed that they had a typical night sleep, consisting of 8—10 hours of sleep, average for adolescents [20]. We did not, however, specifically measure sleep. A cross-over design would have provided additional confirmation at the individual subject level in contrast to our parallel group design.

Our study was limited as the sample was opportune, from a California middle school, and was not epidemiologically based. No subjects approached declined to participate. No accelerated or failing students were included, although this was not a strict exclusion criterion.

The sample population reflected the general school population in this geographic area, although Asians were underrepresented Our sample size was relatively small and limited to early adolescence, ages 10—14, although twice the sample of Prehn-Kristensen et al. The 10—14 age group was deliberately chosen because of the importance of declarative memory on adolescent school performance and related social functioning [21].

Marked changes in sleep and sleep architecture are a defining feature of adolescence [22]. Disorders of adolescence frequently disrupt sleep. Twenty-five to forty percent of adolescents have sleep disorders that can have an important effect on daytime school and consequent social functioning [23].

Sleep disorders are even more prevalent in adolescents with psychiatric disorders and developmental disabilities [24]. It is important to have data on the effects of normal sleep on declarative memory in normal adolescents to better understand the consequences of lack of sleep and abnormal sleep patterns.

We lose our ability to make sound decisions because we can no longer accurately assess the situation, plan accordingly, and choose the correct behavior. Judgment becomes impaired.

Being chronically tired to the point of fatigue or exhaustion means that we are less likely to perform well. Lapses in focus from sleep deprivation can even result in accidents or injury. For more information about how sleep deprivation affects performance, see Sleep, Performance, and Public Safety. Low-quality sleep and sleep deprivation also negatively impact mood, which has consequences for learning. Alterations in mood affect our ability to acquire new information and subsequently to remember that information.

Although current research suggests that sleep is essential for proper memory function, there are unanswered questions, as in any area of active scientific inquiry. For example, certain medications will significantly, if not entirely, suppress REM sleep. However, patients taking these medications do not report any memory impairment.

Exploration and debate continue. Mice exhibit an increase in REM sleep after completing a new course through a maze. Not all researchers are convinced that sleep plays as prominent a role in memory consolidation as others believe.

In experiments in which animals completed a course through a complicated maze, the animals' amount of REM sleep increased after performing the task.

Some researchers believe that the increase in REM sleep reflects an increased demand on the brain processes that are involved in learning a new task.

Other researchers, however, have suggested that any changes in the amount of REM sleep are due to the stress of the task itself, rather than a functional relationship to learning.

Researchers are likewise split with regard to the impact of sleep deprivation on learning and memory. For example, rats often perform much worse on learning tasks after being selectively deprived of REM sleep.

Some scientists have argued that the observed differences in learning are not actually due to the lack of REM sleep, but may be due to the animals not being as well rested because they were deprived a portion of their sleep.

Although open questions and debate remain, the overall evidence suggests that adequate sleep each day is very important for learning and memory. Getting adequate sleep the first night after learning a new skill is important for improving memory and performance.

Print this issue. When you learn something new, the best way to remember it is to sleep on it. It also helps to link new memories to earlier ones. You might even come up with creative new ideas while you slumber. What happens to memories in your brain while you sleep? And how does lack of sleep affect your ability to learn and remember?

NIH-funded scientists have been gathering clues about the complex relationship between sleep and memory. Their findings might eventually lead to new approaches to help students learn or help older people hold onto memories as they age. Matthew Walker, a sleep scientist at the University of California, Berkeley.

While you snooze, your brain cycles through different phases of sleep, including light sleep, deep sleep, and rapid eye movement REM sleep, when dreaming often occurs. The cycles repeat about every 90 minutes. The non-REM stages of sleep seem to prime the brain for good learning the next day.