Sleep-Wake Cycle Biorhythms and Circadian Rhythms

Time also springs from within. There is no doubt that at the micro- as well as at the macro level, life’s rhythms have distinct periodicities embedded in the text of genetic materials. We are aware of sleep-wake cycles and the endogenous rhythms of breathing, heartbeats, and pulses. Plus, we have all seen sine waves of EEGs (alpha brain waves/second) or EKGs (heartbeats/minute) depicted on oscilloscopes, if only on TV, so we are not unfamiliar with bodily rhythms.

Diagnosticians are trained to examine sine waves for both period and amplitude as signs of departures from normal patterns and for cues to disruptions and dysrhthmias. Estimates are that there are over two dozen semiautonomous rhythms ranging from metabolic, hormonal, and neurological activity to composite processes like eating and sleeping.

To a certain extent, each helps shape our sense of time. In the argot of science it would be more appropriate to talk about periodicities, cycles, or oscillations, but rhythms will do for our purposes. These biorhythms are part of what Minkowski (1970) intended when he referred to as lived time. It is not merely that these rhythms mark life’s passage, but that chemical, electrical, and physical oscillations comprise life itself. From cortical neurons to thermal regulation or cognitive reckoning each process has a certain cadence. Whether we are sensitive to rhythms on a routine basis, we may be jolted into awareness when they become desynchronized. The much-storied jet lag or the malaise sometimes associated with shift work are cases in point, but only two of the more obvious examples. It is not too much of an overstatement to say maintaining the cadences is essential to maintaining life—as the beat declines, so, too, does life’s vitality—until it is sapped.

Circadian Rhythms

The category of rhythms occurring in 24-hour cycles are called circadian. There are also longer and shorter endogenous cycles. Many plants and animals have circadian rhythms, and most of us are at least vaguely aware of the diurnal opening and closing of flowers, leaf movement, photosynthesis, or nocturnal animals reflecting oscillating photo or thermal cycles. In humans, circadian rhythms have to do with sleep-wake cycles, thermal treatment regulation, and so on that begin as early as the prenatal phase. A slightly less obvious cycle has to do with optimal cognitive processing normally thought of as attentiveness. In everyday parlance, we speak of “morning people” or “night owls” to characterize people who operate better on one end or the other of the day. Though wakefulness and attentiveness are highly sensitive to external stimuli, they are ready examples of the regularities of our being: there is a time for being attentive and a time for rest.

Many of these rhythms are mediated by environmental conditions and can be reset by light cues, for example, gradually shifting to an alternative cycle if there is reason to do so. To illustrate: scientists know that brain waves can be affected by an array of external stimuli, such as photic activity that can disrupt normal patterns. There may be other environmental factors as well that also affect our internal rhythms. Scientists have barely begun to attend to the possible influences from the earth’s magnetism, gravity, barometric pressure, or atmospheric radiation (Orme, 1969).