What Is Sleep?

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There was a time when people thought that sleep was simply a time when the body and brain “shut off” for a few hours each night to rest in preparation for the next day. But now scientists understand that neither the body nor the brain “shut down” when we sleep; in fact, they are often working even harder than they do during the day, undergoing processes to restore cells, process information, and improve health.

Circadian rhythm

Much like the daily opening and closing of tamarind tree leaves, the human body follows a natural, (approximately) 24-hour pattern called the circadian rhythm. This rhythm is influenced by the environment (such as lightness or darkness) as well as your genetic makeup and determines your sleep patterns by releasing hormones when it’s time to sleep. Abnormalities in the circadian rhythm can lead to sleep disorders like insomnia.

Stages of sleep

view from above of a man sleeping in bedSleep has two main phases—REM and non-REM. We spend about a quarter of our sleeping lives in the REM phase, which is a period of vigorous brain activity, marked by vivid dreams. This stage may be responsible for consolidating information and processing memories, which is why babies (whose entire days are full of new experiences the brain needs to process) spend twice as much time in REM sleep than adults do.

Non-REM sleep has three to four distinct stages (depending on which experts you ask). These grow gradually deeper throughout the night until it becomes very difficult to be disturbed from sleep. During this time, the body works to gently lower the heart rate, temperature, and breathing rate. 

    The purpose of sleep

    Scientists still haven’t pinpointed a succinct reason why animals need to sleep every night. However, based on research and monitoring the brains of sleeping humans, they have some ideas. Among its many functions, sleep:

    1. Offers the body a chance to recover from wear and tear of daily life. Many researchers have suggested the restorative effects of sleeping. This doesn’t just mean that the body rests during sleep—rather, the cells busily regenerate themselves and the body temperature, heart rate, and breathing drop in order to conserve energy.
    2. Facilitates learning & memory. Not only do you need rest to sustain the attention and concentration necessary to learn new tasks, but according to Harvard’s Division of Sleep Medicine, sleep is a time for the brain to consolidate memories, which makes learning new things easier. People who sleep after learning how to play a video game generally perform much better in the game later than those who stay awake. Even more intriguingly, a recent study in Natural Neuroscience showed that people can even learn completely new behaviors (in this case, to associate unpleasant and pleasant odors with certain sounds) while they are completely asleep.
    3. Plays a role in immune function. Your body produces special proteins called cytokines, which help your immune system fight off infection. According to the U.S. Department of Health and Human Services, more of these proteins are produced during sleep when you are sick, which is one of the reasons you may feel so tired when you have the flu. Rest gives the body the time it needs to produce these infection-fighting proteins and to restore itself to wellness.

    Alcohol and sleep

    While many people believe that having a drink will help them get to sleep faster, alcohol actually increases the number of times you awaken during the night, leaving you tired and sleep-deprived the next day.

    http://www.nigms.nih.gov/Education/Factsheet_CircadianRhythms.htm

    http://healthysleep.med.harvard.edu/

    http://www.sleepfoundation.org/article/sleep-topics/children-and-sleep

    http://www.webmd.com/sleep-disorders/excessive-sleepiness-10/sleep-101

    USDHHS – guide to healthy sleep

    http://ngm.nationalgeographic.com/2010/05/sleep/max-text

    Arzi, A., Shedlesky, L., Ben-Shaul, M., Nasser, K., Oksenberg, A., Hairston, I.S., Sobel, N. (20120). Humans can learn new information during sleep. Natural Neuroscience; 15(10), 1460-5.

    Brawn, T.P., Fenn, K.M., Nusbaum, H.C., Margoliash, D. (2008). Consolidation of sensorimotor learning during sleep. Learning & Memory;15(11):815-9.

    Ganz, F.D. (2012). Sleep and immune function. Critical Care Nurse; 32(2), e19-e25.

    Walker, M.P. (2009). The role of sleep in cognition and emotion. Annals of the New York Academy of Sciences;1156, 168-97.