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Research and theories of sleep

To talk about a concept, we mustfirst be clear on its definition. Psychologists describe sleep as an altered state of consciousness. It is a resting state in which an individual becomes relatively quiescent and relatively unaware of the environment. During sleep, which is in part a period of rest and relaxation, most physiological functions such as body temperature, blood pressure, and rate of breathing and heartbeat decrease. The amount of sleep needed depends on both the individual and the environment.
With the invention of the "Electroencephalogram" or an "EEG" as it is more commonly known has made it possible to monitor the brain’s electrical activity. The EEG picks up and records electrical activity through electrodes attached to the scalp. The reading of a waking person is clearly different than that of a sleeping person.
The EEG pattern of our brain during waking periods is very rapid, irregular and low on voltage. This means that many neurons are firing at different intervals and at different times, with different strengths too. This type of irregular electrical activity in the brain during wakefulness is called beta waves or beta activity.
When we are relaxed, sitting in the sofa watching T.V. without any mental arousal, the EEG records a waveform called alpha waves or alpha activity, slower than beta waves. These two waves (alpha and beta) represent the irregular firing pattern of large areas of the brain. Brain activity is desynchronised while in alpha and beta activity.
Sleep on the other hand is not a random process; instead, it is a very organized one. Through EEG readings Sleep has been separated into five stages. Stage 1-4 (non-REM sleep) followed finally by REM sleep. Once REM sleep is achieved, the cycle reverses itself and goes back though stages IV, III, II and again to III, IV and REM. Throughout the night, this cycle occurs at 90 to 100 minute intervals.

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