Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep–wake phase disorder, is the delaying of a person's circadian rhythm compared to those of societal norms. The disorder affects the timing of biological rhythms including sleep, peak period of alertness, core body temperature, and hormonal cycles.
William Charles Dement was an American sleep researcher and founder of the Sleep Research Center at Stanford University. He was a leading authority on sleep, sleep deprivation and the diagnosis and treatment of sleep disorders such as sleep apnea and narcolepsy. For this pioneering work in a previously uncharted field in the United States, he is sometimes referred to as the American father of sleep medicine.
Somnolence is a state of strong desire for sleep, or sleeping for unusually long periods. It has distinct meanings and causes. It can refer to the usual state preceding falling asleep, the condition of being in a drowsy state due to circadian rhythm disorders, or a symptom of other health problems. It can be accompanied by lethargy, weakness and lack of mental agility.
Hypersomnia is a neurological disorder of excessive time spent sleeping or excessive sleepiness. It can have many possible causes and can cause distress and problems with functioning. In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), hypersomnolence, of which there are several subtypes, appears under sleep-wake disorders.
Somnology is the scientific study of sleep. It includes clinical study and treatment of sleep disorders and irregularities. Sleep medicine is a subset of somnology.
The Multiple Sleep Latency Test (MSLT) is a sleep disorder diagnostic tool. It is used to measure the time elapsed from the start of a daytime nap period to the first signs of sleep, called sleep latency. The test is based on the idea that the sleepier people are, the faster they will fall asleep.
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.
Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompassing several sleep disorders where increased sleep is a symptom, or as a symptom of another underlying disorder like narcolepsy, circadian rhythm sleep disorder, sleep apnea or idiopathic hypersomnia.
Sleep medicine is a medical specialty or subspecialty devoted to the diagnosis and therapy of sleep disturbances and disorders. From the middle of the 20th century, research has provided increasing knowledge of, and answered many questions about, sleep–wake functioning. The rapidly evolving field has become a recognized medical subspecialty in some countries. Dental sleep medicine also qualifies for board certification in some countries. Properly organized, minimum 12-month, postgraduate training programs are still being defined in the United States. In some countries, the sleep researchers and the physicians who treat patients may be the same people.
Caffeine-induced sleep disorder is a psychiatric disorder that results from overconsumption of the stimulant caffeine. Caffeine is one of the most widely consumed psychoactive drugs: almost 90% of Americans in a survey consume some type of caffeine each day. "When caffeine is consumed immediately before bedtime or .... throughout the day, sleep onset may be delayed, total sleep time reduced, normal stages of sleep altered, and the quality of sleep decreased." Caffeine reduces slow-wave sleep in the early part of the sleep cycle and can reduce rapid eye movement sleep later in the cycle. Caffeine increases episodes of wakefulness, and high doses in the late evening can increase sleep onset latency. In elderly people, there is an association between use of medication containing caffeine and difficulty in falling asleep.
A sleep study is a test that records the activity of the body during sleep. There are five main types of sleep studies that use different methods to test for different sleep characteristics and disorders. These include simple sleep studies, polysomnography, multiple sleep latency tests (MSLTs), maintenance of wakefulness tests (MWTs), and home sleep tests (HSTs). In medicine, sleep studies have been useful in identifying and ruling out various sleep disorders. Sleep studies have also been valuable to psychology, in which they have provided insight into brain activity and the other physiological factors of both sleep disorders and normal sleep. This has allowed further research to be done on the relationship between sleep and behavioral and psychological factors.
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.
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 period. For years, scientists have been investigating the benefits of napping, including the 30-minute nap as well as sleep durations of 1–2 hours. Performance across a wide range of cognitive processes has been tested.
In chronobiology, a circasemidian rhythm is a physiological arousal cycle that peaks twice in a 24-hour day. It may also be called the semicircadian rhythm. Numerous studies have demonstrated that human circadian rhythms in many measures of performance and physiological activity have a 2-peak daily (circasemidian) pattern. The word, circasemidian, is based upon the Latin words circa ("about"), semi ("half") and dia ("day"). Thus, this is a rhythm that has two cycles per day, and some investigators have referred to it as the semicircadian rhythm. It usually serves to (1) deepen the pre-dawn nadir in body temperature and cognitive performance, (2) create a flat spot during the early afternoon in the daytime increase in body temperature and cognitive performance, and (3) heighten the early-evening peak in body temperature and cognitive performance. Broughton was the first to bring this characteristic of human performance to the attention of researchers.
Irregular sleep–wake rhythm disorder (ISWRD) is a rare form of circadian rhythm sleep disorder. It is characterized by numerous naps throughout the 24-hour period, no main nighttime sleep episode, and irregularity from day to day. Affected individuals have no pattern of when they are awake or asleep, may have poor quality sleep, and often may be very sleepy while they are awake. The total time asleep per 24 hours is normal for the person's age. The disorder is serious—an invisible disability. It can create social, familial, and work problems, making it hard for a person to maintain relationships and responsibilities, and may make a person home-bound and isolated.
Charles Andrew Czeisler is a Hungarian-American physician and sleep and circadian researcher. He is a leading researcher and author in the fields of the effects of light on human physiology, circadian rhythms and sleep medicine.
In the United States, the start school later movement is an interdisciplinary effort by health professionals, sleep researchers, educators, community advocates, parents, students, and other concerned citizens working for school hours that give an opportunity to get more sleep at optimal times. It bases its claims on a growing body of evidence that starting middle and high schools too early in the morning is unhealthy, counterproductive, and incompatible with adolescent sleep needs and patterns. During the second half of the 20th century, many public schools in the United States began shifting instructional time earlier than the more conventional bell time, thought out 9 a.m. Today it is common for American schools to begin the instructional day in the 7 a.m. hour and end about seven hours later, around 2 p.m. Most sleep research suggests that morning classes should begin no earlier than 8:30 a.m. for middle and high school students.
Phyllis C. Zee is the Benjamin and Virginia T. Boshes Professor in Neurology, the director of the Center for Circadian and Sleep Medicine (CCSM) and the chief of the Division of Sleep Medicine (neurology) at the Feinberg School of Medicine, Northwestern University, Chicago. She is also the medical director of Sleep Disorders Center at Northwestern Memorial Hospital.
Adolescent sleep is typically poor in duration and quality. Sleep duration and quality reduce to suboptimal levels, and sleep duration variability and latency increases during adolescence. Sleep recommendations suggest that adolescents should obtain 8–10 hours of sleep per night. Additionally, there is a shift in the body's circadian rhythm such that sleep and wake timings become later during adolescence. Technology, social factors, and physical development are thought to contribute to poor sleep during this time. Poor sleep duration and quality in adolescents has been linked with altered brain functioning and development, poor mental and physical health, as well as higher rates of disease and mortality. The concerns surrounding poor sleep during adolescence has garnered significant public attention, especially concerning policies related to school start times. Many evidences suggest that sleep contributes positively to attention, behavior, and academic achievement for adolescents.
Behavioral sleep medicine (BSM) is a field within sleep medicine that encompasses scientific inquiry and clinical treatment of sleep-related disorders, with a focus on the psychological, physiological, behavioral, cognitive, social, and cultural factors that affect sleep, as well as the impact of sleep on those factors. The clinical practice of BSM is an evidence-based behavioral health discipline that uses primarily non-pharmacological treatments. BSM interventions are typically problem-focused and oriented towards specific sleep complaints, but can be integrated with other medical or mental health treatments. The primary techniques used in BSM interventions involve education and systematic changes to the behaviors, thoughts, and environmental factors that initiate and maintain sleep-related difficulties.
