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The neuroscience of sleep refers to the effect of sleep on the brain and nervous system in the body. Sleep is an essential for the human body to develop and function healthily and it is regulated by several different mechanisms and neurotransmitters in the central nervous system.
This article will discuss the neuroscience of sleep in more detail, including its regulation and function in the body.
Sleep is a naturally recurring state that is marked by reduced or absent consciousness and sensory activity, and inactivity of most voluntary muscles.
There are two main stages of sleep, known as rapid eye movement (REM) and non-rapid eye movement sleep (NREM) or slow wave sleep (SWS). During REM sleep, the brain activity is similar to that of an awake person whereas there are periods of slow waves and synchronized neuron activity present in NREM sleep.
The timing of sleep is regulated by the circadian rhythm, which is the internal body clock of the body that dictates the urge to sleep according to the surrounding environment and light cues.
The circadian rhythm is controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus, which processes light signals from the optic nerve and triggers the release of certain neurotransmitters. It has an intrinsic time that regulates the changes in body temperature, production of cortisol hormone and release of melatonin, all of which has an effect on sleep.
Acetylcholine is an important neurotransmitter in the regulation of sleep in the Pons and the Basal Forebrain of the brain, helping to increase cortical arousal. Other neurotransmitters involved in the regulation of sleep, include GABA, which promotes sleep, and norepinephrine, serotonin, histamine and orexin, which increase alertness and hinder sleep.
Although sleep is considered to be an essential function, it is not entirely clear why it is required, beyond the prevention of sleep deprivation and related consequences. There are, however, several physiological processes that occur in the brain and central nervous system during sleep that are important for bodily functions, although its exact role is still being uncovered.
During REM sleep, for example, the activity of the brain is similar to that of a person who is awake, suggesting that it is not a dormant period and has a specific function. It is during this stage of sleep that vivid dreaming is likely to occur, which is proposed to be a mechanism to replay and process mental stimuli in order to extract meaning and create memories.
It is currently believed by many sleep researchers that the process of sleep is required to systemize the debris in the brain that builds up while an individual is awake. In particular, beta-amyloid in a protein associated with Alzheimer’s disease that is thought to cause harm to the brain tissue and memory function over time. During sleep, channels in the brain allow the cerebrospinal fluid to flush this debris out of the brain tissue, reducing the buildup of toxins and the likelihood of neurodegenerative disease.
It is probable that the purpose and function of sleep in the brain and central nervous system is much deeper that what we are currently aware of and, as sleep research continues to progress, we will continue to discover more about this field.