Sleep onset latency
Encyclopedia
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.
reports early development of the concept, and of the first test for it, the Multiple Sleep Latency Test
(MSLT), in his book The Promise of Sleep. Dement and colleagues including Mary Carskadon
had been seeking an objective measure of daytime sleepiness to help assess the effects of sleep disorders. In the course of evaluating experimental results, they realized that the amount of time it took to fall asleep in bed was closely linked to the subjects' own self-evaluated level of sleepiness. "This may not seem like an earthshaking epiphany, but conceiving and developing an objective measure of sleepiness was perhaps one of the most important advances in sleep science," Dement and coauthor Christopher Vaughn write of the discovery.
When they initially developed the MSLT, Dement and others put subjects in a quiet, dark room with a bed and asked them to lie down, close their eyes and relax. They noted the number of minutes, ranging from 0 to 20, that it took a subject to fall asleep. If a volunteer was still awake after 20 minutes, the experiment was ended and the subject given a maximal alertness/minimal sleepiness rating. When scientists deprived subjects of sleep, they found sleep latency levels could drop below 1, i.e., subjects could fall asleep in less than a minute. The amount of sleep loss was directly linked to changes in sleep latency scores.
The studies eventually led Dement and Carskadon to conclude that "the brain keeps an exact accounting of how much sleep it is owed". Not getting enough sleep during any given period of time leads to a phenomenon called sleep debt
, which lowers sleep latency scores and makes sleep-deprived individuals fall asleep more quickly.
, the "father of sleep research." The subject reclines in a quiet, darkened room and drapes a hand holding a spoon over the edge of the bed or chair, placing a plate on the floor beneath the spoon. After checking the time, the subject tries to relax and fall asleep. When sleep is attained, the spoon will fall and strike the plate, awakening the subject, who then checks to see how much time has passed. The number of minutes passed is the sleep onset latency at that particular hour on that particular day.
Dement advises against doing these evaluations at night when sleep onset latency can naturally be lower, particularly in older people. Instead, he suggests testing sleep onset latency during the day, ideally at 10:00 a.m., 12:30 p.m. and 3:00 p.m. A sleep onset latency of 0 to 5 minutes indicates severe sleep deprivation, 5 to 10 minutes is "troublesome," 10 to 15 minutes indicates a mild but "manageable" degree of sleep debt, and 15 to 20 minutes is indicative of "little or no" sleep debt.
| Minutes | Sleepiness |
|---|---|
| 0–5 | Severe |
| 5–10 | Troublesome |
| 10–15 | Manageable |
| 15–20 | Excellent |
Sleep latency studies
Pioneering Stanford University sleep researcher William C. DementWilliam C. Dement
William Charles Dement is a pioneering US sleep researcher, and founder of the Sleep Research Center, the world's first sleep laboratory, at Stanford University. He is a leading authority on sleep, sleep deprivation, and the diagnosis and treatment of sleep disorders such as sleep apnea and...
reports early development of the concept, and of the first test for it, the Multiple Sleep Latency Test
Multiple Sleep Latency Test
The Multiple Sleep Latency Test 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...
(MSLT), in his book The Promise of Sleep. Dement and colleagues including Mary Carskadon
Mary Carskadon
Mary A. Carskadon, Ph.D., is a Professor in the Department of Psychiatry and Human Behavior at the Warren Alpert Medical School of Brown University. She is also the Director of the at E.P. Bradley Hospital. She is considered to be an expert on sleep and circadian rhythms during childhood and...
had been seeking an objective measure of daytime sleepiness to help assess the effects of sleep disorders. In the course of evaluating experimental results, they realized that the amount of time it took to fall asleep in bed was closely linked to the subjects' own self-evaluated level of sleepiness. "This may not seem like an earthshaking epiphany, but conceiving and developing an objective measure of sleepiness was perhaps one of the most important advances in sleep science," Dement and coauthor Christopher Vaughn write of the discovery.
When they initially developed the MSLT, Dement and others put subjects in a quiet, dark room with a bed and asked them to lie down, close their eyes and relax. They noted the number of minutes, ranging from 0 to 20, that it took a subject to fall asleep. If a volunteer was still awake after 20 minutes, the experiment was ended and the subject given a maximal alertness/minimal sleepiness rating. When scientists deprived subjects of sleep, they found sleep latency levels could drop below 1, i.e., subjects could fall asleep in less than a minute. The amount of sleep loss was directly linked to changes in sleep latency scores.
The studies eventually led Dement and Carskadon to conclude that "the brain keeps an exact accounting of how much sleep it is owed". Not getting enough sleep during any given period of time leads to a phenomenon called sleep debt
Sleep debt
Sleep debt or sleep deficit is the cumulative effect of not getting enough sleep. A large sleep debt may lead to mental and/or physical fatigue....
, which lowers sleep latency scores and makes sleep-deprived individuals fall asleep more quickly.
Home testing of sleep latency
For home-testing for an unusually low sleep latency and potential sleep deprivation, the authors point to a technique developed by Nathaniel KleitmanNathaniel Kleitman
Nathaniel Kleitman was Professor Emeritus in Physiology at the University of Chicago. Author of the seminal 1939 book Sleep and Wakefulness, he is recognized as the father of American sleep research...
, the "father of sleep research." The subject reclines in a quiet, darkened room and drapes a hand holding a spoon over the edge of the bed or chair, placing a plate on the floor beneath the spoon. After checking the time, the subject tries to relax and fall asleep. When sleep is attained, the spoon will fall and strike the plate, awakening the subject, who then checks to see how much time has passed. The number of minutes passed is the sleep onset latency at that particular hour on that particular day.
Dement advises against doing these evaluations at night when sleep onset latency can naturally be lower, particularly in older people. Instead, he suggests testing sleep onset latency during the day, ideally at 10:00 a.m., 12:30 p.m. and 3:00 p.m. A sleep onset latency of 0 to 5 minutes indicates severe sleep deprivation, 5 to 10 minutes is "troublesome," 10 to 15 minutes indicates a mild but "manageable" degree of sleep debt, and 15 to 20 minutes is indicative of "little or no" sleep debt.