Neuroscience of sleep

The neuroscience of sleep is the study of the neuroscientific and physiological basis of the nature of sleep and its functions. Traditionally, sleep has been studied as part of psychology and medicine. The study of sleep from a neuroscience perspective grew to prominence with advances in technology and proliferation of neuroscience research from the second half of the twentieth century.

The fact that organisms daily spend hours of their time in sleep and that sleep deprivation can have disastrous effects ultimately leading to death, demonstrate the importance of sleep. For a phenomenon so important, the purposes and mechanisms of sleep are only partially understood, so much so that as recently as the late 1990s it was quipped: "The only known function of sleep is to cure sleepiness". However, the development of improved imaging techniques like EEG, PET and fMRI, along with high computational power have led to an increasingly greater understanding of the mechanisms underlying sleep.

The fundamental questions in the neuroscientific study of sleep are:

Other areas of modern neuroscience sleep research include the evolution of sleep, sleep during development and aging, animal sleep, mechanism of effects of drugs on sleep, dreams and nightmares, and stages of arousal between sleep and wakefulness.

Rapid eye movement sleep (REM), non-rapid eye movement sleep (NREM or non-REM), and waking represent the three major modes of consciousness, neural activity, and physiological regulation. NREM sleep itself is divided into multiple stages – N1, N2 and N3. Sleep proceeds in 90-minute cycles of REM and NREM, the order normally being N1 → N2 → N3 → N2 → REM. As humans fall asleep, body activity slows down. Body temperature, heart rate, breathing rate, and energy use all decrease. Brain waves get slower and bigger. The excitatory neurotransmitter acetylcholine becomes less available in the brain. Humans often maneuver to create a thermally friendly environment—for example, by curling up into a ball if cold. Reflexes remain fairly active.

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