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History and Measurement of Chronotype: – Nathaniel Kleitman summarized sleep knowledge in 1939, proposing the rest-activity cycle. – O. Öquist’s 1970 thesis marked modern research […]

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History and Measurement of Chronotype:
– Nathaniel Kleitman summarized sleep knowledge in 1939, proposing the rest-activity cycle.
– O. Öquist’s 1970 thesis marked modern research into chronotypes.
– Various questionnaires like the Morningness-Eveningness Questionnaire and Munich Chronotype Questionnaire assess chronotypes.
– Composite scales like the Composite Scale of Morningness have been developed for measuring chronotypes.
– The Lark-Owl Chronotype Indicator and Circadian Type Inventory are tools used for assessing sleeping rhythms.

Characteristics and Sleep Patterns of Chronotype:
– Morningness-eveningness follows a normal distribution.
– Chronotype is largely independent of ethnicity, gender, and socioeconomic status.
– Morning types have earlier peak daytime temperatures and sleep/wake timings.
– No significant differences in sleep lengths between morning and evening types.
– Age is a factor to consider in assessing morningness and eveningness.

Diurnal Rhythms, Personality, and Intelligence in Chronotype:
– Diurnal variations include body temperature and pain sensitivity differences between morning and evening types.
– Chronotypes show differences in personality traits, creativity, and intellectual domains.
– Evening chronotypes are associated with higher intelligence levels.
– Genetic variants near genes regulating circadian rhythms and photoreception influence chronotypes.
– Disrupted circadian rhythms can be linked to various diseases and body mass index.

Genetic Variants and Disease Associated with Chronotype:
– 22 genetic variants are linked to chronotype, including variants near genes like RGS16 and PER2.
– Genetic factors play a role in determining chronotype.
– Chronotype is genetically correlated with body mass index.
– Disrupted circadian rhythms are associated with various diseases and may affect susceptibility to diseases.
– Research indicates a genetic link between chronotype and BMI.

Chronotype, Health, and Performance:
– Circadian rhythms influence sleep-wake cycles and health outcomes.
– Response to pain can be influenced by chronotype.
– Morning types show better cognitive performance in the morning, while evening types may peak in the evening.
– Chronotype can impact metabolic health and response to shift work.
– Academic achievement and creative thinking may vary based on individual chronotypes.

Chronotype (Wikipedia)

A chronotype is the behavioral manifestation of underlying circadian rhythm's myriad of physical processes. A person's chronotype is the propensity for the individual to sleep at a particular time during a 24-hour period. Eveningness (delayed sleep period; most active and alert in the evening) and morningness (advanced sleep period; most active and alert in the morning) are the two extremes with most individuals having some flexibility in the timing of their sleep period. However, across development there are changes in the propensity of the sleep period with pre-pubescent children preferring an advanced sleep period, adolescents preferring a delayed sleep period and many elderly preferring an advanced sleep period.

The causes and regulation of chronotypes, including developmental change, individual propensity for a specific chronotype, and flexible versus fixed chronotypes have yet to be determined. However, research is beginning to shed light on these questions, such as the relationship between age and chronotype. There are candidate genes (called CLOCK genes) that exist in most cells in the body and brain, referred to as the circadian system that regulate physiological phenomena (hormone levels, metabolic function, body temperature, cognitive faculties, and sleeping). With the exception of the most extreme and rigid chronotypes, regulation is likely due to gene-environment interactions. Important environmental cues (zeitgebers) include light, feeding, social behavior, and work and school schedules. Additional research has proposed an evolutionary link between chronotype and nighttime vigilance in ancestral societies.

Humans are normally diurnal creatures that are active in the daytime[citation needed]. As with most other diurnal animals, human activity-rest patterns are endogenously regulated by biological clocks with a circadian (~24-hour) period [citation needed]. Chronotypes have also been investigated in other species, such as fruit flies and mice.

Normal variation in chronotype encompasses sleep–wake cycles that are two to three hours later in evening types than morning types. Extremes outside of this range can cause a person difficulty in participating in normal work, school, and social activities. If a person's "lark" or (more commonly) "owl" tendencies are strong and intractable to the point of disallowing normal participation in society, the person is normally considered to have a circadian rhythm sleep disorder.

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