Although we still have many unanswered questions about why we spend one third of our lives sleeping, we do know that lack of sleep can have many negative effects. In a genetic condition known as fatal familial insomnia, middle-aged people gradually lose the ability to sleep. As the name of the disorder implies, the result of this sleep loss is eventual death. The exact cause of death is unknown, although the disorder is associated with damage to the thalamus (Gallassi et al., 1996).
Sleep, and in particular Stages 3 and 4 of N-REM sleep, plays an important role in repairing the body. Sleep deprivation slows the healing of injuries (Murphy et al., 2007), reduces the activity of the immune system (Zager, Andersen, Ruiz, Antunes, & Tufik, 2007) and results in the production of fewer new neurons in adult brains (Guzman-Marin et al., 2003). The vast majority of the release of human growth hormone, which plays important roles in repairing the body, occurs during Stages 3 and 4 of N-REM sleep (Savine & Sönksen, 2000). Another line of evidence supporting the restorative hypothesis of sleep is the behavior of people following intense physical activity. Runners competing in ultramarathons (races that are twice the length of a normal marathon) experience greater amounts of N-REM sleep the night after their performance. It is possible to selectively deprive volunteers in a sleep laboratory of Stages 3 and 4 N-REM sleep. After a night of such deprivation, volunteers typically complain of muscle and joint pain (Moldofsky & Scarisbrick, 1976). Because time spent in N-REM decreases about one half hour per decade after the age of 50 (Van Cauter, Leproult, & Plat, 2000), it is possible that reduced N-REM is the source of some of the muscle and joint aches and pains experienced by older adults.
Sleep plays a significant role in the consolidation of memories. Staying up all night results in poor memory performance, and two subsequent nights of normal sleep do not make up for the initial sleep deprivation effects (Stickgold & Walker, 2007). Memories for verbal tasks, emotional material, and procedures are all better following a period of sleep than when followed by wakefulness (Gais & Born, 2004; Wagner, Fischer, & Born, 2002; Wagner, Gais, & Born, 2001). Needless to say, students WHO wish to retain the material they’ve studied would be well advised to get a good night’s sleep.