Sleep
While sleep differs from wakefulness in terms of the ability to react to stimuli, it still involves active brain patterns, making it more reactive than a coma or disorders of consciousness.
[5] Sleep is a highly conserved behavior across animal evolution,[6] likely going back hundreds of millions of years,[7] and originating as a means for the brain to cleanse itself of waste products.
In areas with reduced activity, the brain restores its supply of adenosine triphosphate (ATP), the molecule used for short-term storage and transport of energy.
In other words, sleeping persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events.
[15] Key physiological methods for monitoring and measuring changes during sleep include electroencephalography (EEG) of brain waves, electrooculography (EOG) of eye movements, and electromyography (EMG) of skeletal muscle activity.
It is the main occasion for dreams (or nightmares), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone,[20] and suspension of homeostasis.
[17] Awakening can mean the end of sleep, or simply a moment to survey the environment and readjust body position before falling back asleep.
[29] Determinants of alertness after waking up include quantity/quality of the sleep, physical activity the day prior, a carbohydrate-rich breakfast, and a low blood glucose response to it.
[31][26] The suprachiasmatic nucleus (SCN), a brain area directly above the optic chiasm, is presently considered the most important nexus for this process; however, secondary clock systems have been found throughout the body.
If an entrained human is isolated in a bunker with constant light or darkness, he or she will continue to experience rhythmic increases and decreases of body temperature and melatonin, on a period that slightly exceeds 24 hours.
Under natural conditions, light signals regularly adjust this period downward, so that it corresponds better with the exact 24 hours of an Earth day.
Exposure to even small amounts of light during the night can suppress melatonin secretion, and increase body temperature and wakefulness.
[27] Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts), long-distance travel, and the influence of universal indoor lighting.
Process S is driven by the depletion of glycogen and accumulation of adenosine in the forebrain that disinhibits the ventrolateral preoptic nucleus, allowing for inhibition of the ascending reticular activating system.
[38] Sleep deprivation tends to cause slower brain waves in the frontal cortex, shortened attention span, higher anxiety, impaired memory, and a grouchy mood.
Adenosine levels increase in the cortex and basal forebrain during prolonged wakefulness, and decrease during the sleep-recovery period, potentially acting as a homeostatic regulator of sleep.
The siesta habit has recently been associated with a 37% lower coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep.
[47] Short naps at mid-day and mild evening exercise were found to be effective for improved sleep, cognitive tasks, and mental health in elderly people.
[67] The timing is correct when the following two circadian markers occur after the middle of the sleep episode and before awakening:[37] maximum concentration of the hormone melatonin, and minimum core body temperature.
[73][74][75] Researchers have found that sleeping 6–7 hours each night correlates with longevity and cardiac health in humans, though many underlying factors may be involved in the causality behind this relationship.
This can look differently among families, but will generally consist of a set of rituals such as reading a bedtime story, a bath, brushing teeth, and can also include a show of affection from the parent to the child such a hug or kiss before bed.
[95] Sleep may facilitate the synthesis of molecules that help repair and protect the brain from metabolic end products generated during waking.
[101][102] This assumption is based on the active system consolidation hypothesis, which states that repeated reactivations of newly encoded information in the hippocampus during slow oscillations in NREM sleep mediate the stabilization and gradual integration of declarative memory with pre-existing knowledge networks on the cortical level.
These are elusive and mostly unpredictable first-person experiences which seem logical and realistic to the dreamer while they are in progress, despite their frequently bizarre, irrational, and/or surreal qualities that become apparent when assessed after waking.
In a preliminary study, dreamers were able to consciously communicate with experimenters via eye movements or facial muscle signals, and were able to comprehend complex questions and use working memory.
[143] A varied diet containing fresh fruits and vegetables, low saturated fat, and whole grains may be optimal for individuals seeking to improve sleep quality.
These choices are shaped by a variety of factors, such as climate, protection from predators, housing type, technology, personal preference, and the incidence of pests.
In medieval Irish tradition, in order to become a filí, the poet was required to undergo a ritual called the imbas forosnai, in which they would enter a mantic, trancelike sleep.
[158] The American author Washington Irving's short story "Rip Van Winkle", first published in 1819 in his collection of short stories The Sketch Book of Geoffrey Crayon, Gent.,[159][164] is about a man in colonial America named Rip Van Winkle who falls asleep on one of the Catskill Mountains and wakes up twenty years later after the American Revolution.
Insights about differences of the living sleeping brain to its wakeful state and the transition period may have implications for potential explanations of human subjective experience, the so-called hard problem of consciousness, often delegated to the realm of philosophy, including neurophilosophy[165][166][167][168] (or in some cases to religion and similar approaches).
