A pattern centered around behavioral, biochemical, or physiological fluctuation whose period is shorter than a circadian rhythm. These periods usually range from several minutes to hours. Ultradian rhythms can be a part of a circadian rhythm. For example, humans have a 90 minute ultradian cycle of within the circadian sleep-wake cycle. 

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- Circadian rhythms
- Infradian rhythms
- Ultradian rhythms
- Free-running

Types of biological rhythms and clocks

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

A pattern centered around behavioral, biochemical, or physiological fluctuation whose period is longer than a circadian rhythm. Frequency of occurrence is less than once per day. Examples include the menstrual cycle, or seasonal shifts in body weight.

- Circannual 

Infradian rhythms

Ultradian rhythms

A rhythm of behavior shown by an animal deprived of external cues about time of day, where the animal maintains its own cycle. Not exactly 24 hours long. Otherwise known as the natural rhythm, it is not just a reflection of external cues. 

Free-running

A pattern centered around behavioral, biochemical, or physiological fluctuation that repeats every 24 hours. Major value of a circadian rhythm is synchronizing behaviors and body states with environmental changes, providing temporal organization. 

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