Polyphasic sleep or segmented sleep is the system of sleeping during multiple periods over the course of 24 hours, in contrast to monophasic sleep, a single period of sleep within 24 hours. Polyphasic usually means more than two periods of sleep, as distinct from biphasic (or diphasic, bifurcated, or bimodal) sleep, meaning two periods of sleep. The term polyphasic sleep was first used in the early 20th century by psychologist J. S. Szymanski, who observed daily fluctuations in activity patterns. While today monophasic sleep is the norm, historical analysis suggests that polyphasic nighttime sleep was common practice across societies before industrialization. Scientific experiments and observational studies have supported a theory of biphasic sleep in humans. Polyphasic sleep is common in many animals, and is believed to be the ancestral sleep state for mammals, although simians are monophasic. A common practice of biphasic sleep is a nap, a short period of daytime sleep in addition to nighttime sleep. An example of involuntary polyphasic sleep is the circadian rhythm disorder irregular sleep–wake syndrome. The term polyphasic sleep is also used by an online community that experiments with alternative sleeping schedules in an attempt to increase productivity. There is no scientific evidence that this practice is effective or beneficial.
Historical examples
Biphasic sleep (also referred to as segmented sleep, or bimodal sleep) is a pattern of sleep which is divided into two segments, or phases, in a 24-hour period.
First sleep and second sleep One biphasic sleep pattern, sometimes described as segmented sleep, involved sleeping in two phases, separated by about an hour of wakefulness. This pattern was common in preindustrial societies, and it was most common to sleep early ("first sleep"), wake around midnight, and return to bed later ("second sleep"). Along with a nap in the day, it has been argued that this is the natural pattern of human sleep in long winter nights. A case has been made that maintaining such a sleep pattern may be important in regulating stress. Historian A. Roger Ekirch has argued that before the Industrial Revolution, interrupted sleep was dominant in Western civilization. Ekirch asserts that the intervening period of wakefulness was used to pray and reflect, and to interpret dreams, which were more vivid at that hour than upon waking in the morning. This was also a favorite time for scholars and poets to write uninterrupted, whereas still others visited neighbors, engaged in sexual activity, or committed petty crime. This period of wakefulness was known as "the watch". Ekirch draws evidence from more than 500 references to a segmented sleeping pattern in documents from the ancient, medieval, and modern world. Other historians, such as Craig Koslofsky, have endorsed Ekirch's analysis. Ekirch suggests that it is due to the modern use of electric lighting that most modern humans do not practice interrupted sleep. Some have proposed that a sleep pattern based on the historical biphasic sleep schedule might be beneficial, but there is no widespread agreement on this. A 2015 study of three non-industrial equatorial societies showed that all three experienced monophasic nighttime sleep, but the authors' conclusions were questioned by Ekirch.
Single nap (siesta)
Another classic cultural example of a biphasic sleep pattern is the siesta, a nap taken in the early afternoon, often after eating lunch. Such a period of sleep is a common tradition in some countries, particularly those with a warm climate, where it allows people to avoid sunshine and heat during the hottest part of the day; many businesses in these countries open early in the morning (again to avoid the heat), close at 1 p.m. so employees can go home for a siesta, reopen at 3 p.m., and close at around 8 p.m. Historically common throughout the Mediterranean and Southern Europe, it is the traditional daytime sleep of China, Cyprus, Malta, Greece, India, Italy, Portugal, South Africa, Spain, and (through Spanish influence) the Philippines and Hispanic America. In modern times, fewer Spaniards take a daily siesta, ostensibly due to more demanding work schedules.
Modern proposals
The Everyman schedule involves sleeping 3 hours during the night ("core sleep"), and taking three 20-minute naps during the day. This totals 4 hours of sleep in a 24-hour period. The Uberman sleep schedule consists of a 30-minute nap every four hours, totaling 3 hours of sleep in a 24-hour period. Other variations of this sleep pattern involve 8 naps throughout the day, or 20-minute sleep intervals as opposed to 30 minutes. Buckminster Fuller described a regimen consisting of 30-minute naps every six hours. The short article about Fuller's nap schedule in Time in 1943, which referred to the schedule as "intermittent sleeping", says that he maintained it for two years, and notes that "he had to quit because his schedule conflicted with that of his business associates, who insisted on sleeping like other men." This schedule is likely the most extreme type of polyphasic sleep schedule, totaling only two hours of sleep in a 24-hour period.
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