Sleep and Memory

October 8, 2006 Most adults need seven to ten hours of sleep a night. However, a recent poll by the National Sleep Foundation found 40 percent of American adults are getting less than seven hours of sleep/night on weekdays. On average, most people are sleeping 6.8 hours per weekday night and 7.4 hours on a weekend night. Lack of quality sleep can take a toll on the body and mind. People who are sleep-deprived have more difficulty paying attention and staying focused. Reaction time is slowed and decision making skills can be impaired. Sleepiness can affect mood and lead to strained family relationships and poor school or work performance. Annually, sleepy drivers are believed to cause more than 100,000 automobile accidents. The National Sleep Foundation estimates daytime sleepiness costs this country about $100 billion. Memory There are several different types of memory. Short term memory works like a temporary file and has limited capacity. As new information comes in, old information can be lost or "forgotten." Long-term memory can be divided into two different categories. Procedural memory refers to the ability to store and retrieve information related to perception, motor and verbal skills and cognitive thought. Examples of procedural memory are learning to ride a bike or play the piano. Declarative memory refers to factual information that can be consciously recalled. It can be further divided into "episodic memory" (i.e., remembrance of situations, like a first date or vacation) and "semantic memory" (factual information, like addition skills, vocabulary or history). The Role of Sleep in Memory Research has shown that sleep is essential to learning and memory. The exact role of sleep in memory isnt known. However, scientists believe that, during sleep, the brain actively processes, reinforces and relocates new information. At Brigham and Women`s Hospital in Boston, investigators tested the effects of sleep on declarative memory (the ability to remember "facts"). Participants were asked to memorize a series of 20 paired words during evening hours. The next morning (12 hours later), the subjects were given a recall test. Prior to the recall, half of the participants were given a second group of paired words to study. These new words were introduced in an attempt to "distract" the brain, or create interference in recall of the first set of words. To study the effects of sleep, another group of participants was given the first set of words at the beginning of the day and tested later in the day. The researchers found sleep had an important influence on the ability to recall the first set of words. In the non-interference group (those who didnt have to learn the second set of words), participants who slept after learning the first set of words had a slightly higher recall rate than those in the non-sleep group (who learned the words the same morning). In the interference group, those who slept had significantly higher rates of recall than the non-sleep learners. Neurologist Jeffrey Ellenbogen, M.D., says this is the first study to show the benefits of sleep for declarative memory. He says the study may be a "wake-up" call to students who often spend all night studying for exams. Sleep appears to be an important tool for the brain to make stronger connections for stored facts. Those who stay up all night to cram for an exam may perform decently on the next days test. However, later recall of the information may be impaired because the brain hasnt had enough time to "set" those facts. 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