ultradianrytmer

Ultradian rytmer (ultradian rhythms) are recurrent biological cycles with a period shorter than 24 hours. They occur across physiology and behavior and can interact with circadian rhythms to shape daily patterns.

In humans, the most familiar ultradian rhythm appears in sleep. The sleep cycle repeats roughly every 90 to 110 minutes, cycling through stages of non-REM and REM sleep. Hormonal activity also often follows ultradian patterns. Growth hormone is released in pronounced pulses about every 1.5 to 2 hours during deep sleep, while cortisol and other hormones show shorter pulsatile release throughout the day and night.

Beyond sleep and hormones, ultradian processes include digestive activity, fluctuations in appetite-related hormones, and variations in autonomic arousal and core body temperature. These rhythms can be detected with electroencephalography, hormonal assays, heart rate variability, and temperature monitoring.

Mechanisms underlying ultradian rhythms involve multiple oscillator systems, including neural pacemakers in the hypothalamus and brainstem, peripheral clocks, and feedback loops within the hypothalamic-pituitary axis. The study of ultradian rhythms is parallel to research on circadian rhythms (roughly 24 hours) and infradian rhythms (longer than a day), highlighting how shorter cycles influence sleep, endocrinology, metabolism, and behavior across species.