The basic rest–activity cycle (BRAC) is a physiological arousal mechanism in humans proposed by

Nathaniel Kleitman Nathaniel Kleitman (April 26, 1895 – August 13, 1999) was an American physiologist and sleep researcher who served as Professor Emeritus in Physiology at the University of Chicago. He is recognized as the father of modern sleep research, an ...

, hypothesized to occur during both

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...

and

wakefulness Wakefulness is a daily recurring Human brain, brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world. Being awake is the opposite of ...

. Empirically, it is an

ultradian rhythm In chronobiology, an ultradian rhythm is a recurrent period or cycle repeated throughout a 24-hour day. In contrast, circadian rhythms complete one cycle daily, while infradian rhythms such as the human menstrual cycle have periods longer than a ...

of approximately 90 minutes (80–120 minutes) characterized by different levels of excitement and rest. The cycle is mediated by the human biological clock. It is most readily observed in stages of sleep, for example,

rapid eye movement sleep Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...

(REM) and the delta activity cycle. When awake, brainwaves are faster during the first half of the cycle which corresponds to feeling alert and focused. During the last 20 minutes brainwaves slow and as the body feels dreamy or tired. In this phase the body is being readied for the alertness that comes at the beginning of the following cycle. Kleitman hypothesized that the short-term 50 minute ultradian cycle of infants observed by researchers Denisova and Figurin ensured that a newborn infant would have frequent opportunities to respond to the stimulus of hunger pangs by waking up and crying, and would therefore get adequate nutrition. This hypothesis influenced him to consider BRAC as a fundamental human physiological process. Kleitman concluded that BRAC tended to lengthen with age based on research published from Ohlmeyer and Brilmeyer. As early as 1977, other investigators argued that there was no evidence for a "basic rest-activity cycle" outside of sleep cycles. More recent meta-analysis of studies suggest overwhelming evidence for ultradian cycles during wakefulness (affecting things like focus or reaction time) but that the daytime cycles operate via different mechanisms than those causing REM-NREM cycles at night. Despite research centering on the nocturnal evidence, the BRAC is often used as a time management and productivity tool.

References

Human biology Chronobiology {{neuroscience-stub