Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and inhibition of nearly all voluntary muscles during rapid eye movement (REM) sleep, and reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli, but more reactive than a coma or disorders of consciousness, with sleep displaying different, active brain patterns.
Jet lag is a physiological condition that results from alterations to the body's circadian rhythms caused by rapid long-distance trans-meridian travel. For example, someone flying from New York to London, i.e. from west to east, feels as if the time were five hours earlier than local time, and someone travelling from London to New York, i.e. from east to west, feels as if the time were five hours later than local time. The phase shift when traveling from east to west is referred to as phase-delay of the circadian circle, whereas going west to east is phase-advance of the circadian circle. Most travelers find that it is harder to timezone adjust when traveling to the east. Jet lag was previously classified as one of the circadian rhythm sleep disorders.
A circadian rhythm, or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism and responds to the environment. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in animals, plants, fungi and cyanobacteria.
Chronobiology is a field of biology that examines timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος, and biology, which pertains to the study, or science, of life. The related terms chronomics and chronome have been used in some cases to describe either the molecular mechanisms involved in chronobiological phenomena or the more quantitative aspects of chronobiology, particularly where comparison of cycles between organisms is required.
Seasonal affective disorder (SAD) is a mood disorder subset, in which people who have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year, most commonly in winter. Common symptoms include sleeping too much, having little to no energy, and overeating. The condition in the summer can include heightened anxiety.
Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep–wake phase disorder, is a delaying of a person's circadian rhythm, compared to those of the general population and societal norms. The disorder affects the timing of sleep, peak period of alertness, the core body temperature, rhythm, hormonal as well as other daily cycles. People with DSPD generally fall asleep some hours after midnight and have difficulty waking up in the morning. People with DSPD probably have a circadian period significantly longer than 24 hours. Depending on the severity, the symptoms can be managed to a greater or lesser degree, but no cure is known, and research suggests a genetic origin for the disorder.
The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep. It is sometimes called the ultradian sleep cycle, sleep–dream cycle, or REM-NREM cycle, to distinguish it from the circadian alternation between sleep and wakefulness. In humans, this cycle takes 70 to 110 minutes.
Biphasic sleep is the practice of sleeping during two periods over the course of 24 hours, while polyphasic sleep refers to sleeping multiple times—usually more than two. Each of these is in contrast to monophasic sleep, which is one period of sleep within 24 hours. Segmented sleep and divided sleep may refer to polyphasic or biphasic sleep, but may also refer to interrupted sleep, where the sleep has one or several shorter periods of wakefulness, as was the norm for night sleep in pre-industrial societies. A common form of biphasic or polyphasic sleep includes a nap, which is a short period of sleep, typically taken between the hours of 9 am and 9 pm as an adjunct to the usual nocturnal sleep period. Napping behaviour during daytime hours is the simplest form of polyphasic sleep, especially when the nap(s) are taken on a daily basis.
Non-24-hour sleep–wake disorder is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in a society". Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light–dark cycle in nature. Although this sleep disorder is more common in blind people, affecting up to 70% of the totally blind, it can also affect sighted people. Non-24 may also be comorbid with bipolar disorder, depression, and traumatic brain injury. The American Academy of Sleep Medicine (AASM) has provided CRSD guidelines since 2007 with the latest update released in 2015.
A zeitgeber is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
Circadian rhythm sleep disorders (CRSD), also known as circadian rhythm sleep-wake disorders (CRSWD), are a family of sleep disorders which affect the timing of sleep. CRSDs arise from a persistent pattern of sleep/wake disturbances that can be caused either by dysfunction in one's biological clock system, or by misalignment between one's endogenous oscillator and externally imposed cues. As a result of this mismatch, those affected by circadian rhythm sleep disorders have a tendency to fall asleep at unconventional time points in the day. These occurrences often lead to recurring instances of disturbed rest, where individuals affected by the disorder are unable to go to sleep and awaken at "normal" times for work, school, and other social obligations. Delayed sleep phase disorder, advanced sleep phase disorder, non-24-hour sleep–wake disorder and irregular sleep–wake rhythm disorder represents the four main types of CRSD.
In sleep science, sleep onset latency (SOL) is the length of time that it takes to accomplish the transition from full wakefulness to sleep, normally to the lightest of the non-REM sleep stages.
Norman E. Rosenthal is a South African author, psychiatrist and scientist who in the 1980s first described seasonal affective disorder (SAD), and pioneered the use of light therapy for its treatment
A nap is a short period of sleep, typically taken during daytime hours as an adjunct to the usual nocturnal sleep period. Naps are most often taken as a response to drowsiness during waking hours. A nap is a form of biphasic or polyphasic sleep, where the latter terms also include longer periods of sleep in addition to one single period.
Rütger Wever was a German scientist, known for his significant contributions to the field of Chronobiology, including some of the first experiments on humans in time isolated environments.
Michael Terman is an American psychologist best known for his work in applying the biological principles of the circadian timing system to psychiatric treatments for depression and sleep disorders. This subspecialty is known as Chronotherapeutics.
Studies, which include laboratory investigations and field evaluations of population groups that are analogous to astronauts, provide compelling evidence that working long shifts for extended periods of time contributes to sleep deprivation and can cause performance decrements, health problems, and other detrimental consequences, including accidents, that can affect both the worker and others.
The bunker experiment was a scientific experiment that began in 1966 to test whether humans, like other species, have an intrinsic circadian clock. It was started by Jürgen Aschoff and Rütger Wever of the Max Planck Institute for Behavioral Physiology and later taken over by Jürgen Zulley. Participants lived in a bunker for multiple weeks while scientists measured their daily rhythms in many variables. The main conclusion of the experiment was that humans have an intrinsic clock with a period greater than 24 hours. The experiment also established many features of this clock and paved the way for future circadian studies.
Familial sleep traits are heritable variations in sleep patterns, resulting in abnormal sleep-wake times and/or abnormal sleep length.
Charmane Eastman is an American academic research scientist whose career has focused on studying circadian rhythms and their relationships to sleep, jet lag, and shift work. She has also studied winter depression, more properly known as seasonal affective disorder (SAD). Of special focus are the effects of bright light and melatonin on circadian rhythms.
