Ultradian rhythmicity involves biological processes that repeat one or more times within a 24-hour period. Their period is shorter than a full day and exhibits a very wide variety. For example, the period length ranges from a few milliseconds to several hours. Extremely diverse can also be the mechanism and function of ultradian rhythmicity.
What is ultradian rhythmicity?
One of the most interesting ultradian rhythms has period lengths of about four hours and is exemplified in infants. Before they can sleep through the night, they are hungry and awake after about four hours. The ultradian rhythm occurs, for example, in physiological processes such as breathing, blood circulation, hormone production, sleep cycles, the beating of the heart and cell division. It can also be measured concretely in behavioral processes and the eating habits of humans. In contrast to the ultradian rhythm, the period length of the circadian rhythm is one day and that of the infradian rhythm is over one day. Ultradian oscillations and other movements take place in all known biological systems and can be traced down to the level of cells and bacteria. A significant example are the leaf movements of plants, which repeat themselves with regularity. The daily routine of birds, which follows a fixed rhythm, can be observed very well. Cows on the pasture also do not chew at random, but are animated to do so by a clock in their brain. Field mice, on the other hand, eat in very specific cycles that are controlled exclusively by the precaution against starvation. The pituitary gland (hypophysis) in humans secretes its hormones in an absolutely fixed ultradian rhythm. This ultradian rhythm is controlled by various biochemical processes in the cells, which also proceed cyclically. The biosynthesis of protein is an example of these processes, which run like clockwork. Often, those rhythmic processes are even more or less independent of external temperature influences.
Function and task
One of the most interesting ultradian rhythms has period lengths of about four hours and is exemplified in infants. Before they can sleep through the night, they are hungry and awake after about four hours. Nothing can stop them from this. Adults, too, have generally divided their daily diet in such a way that three to four hours pass between each meal. In the ultradian rhythm, the change between the different sleep stages of humans also takes place. Here the period is usually 70 to 110 minutes. Accordingly, a healthy person goes through four to seven sleep cycles per night, in which different deep and shallow forms of sleep alternate according to a certain pattern (REM-Non-REM sleep). Depending on the stage of sleep, the electrical responsiveness of the brain varies significantly. Likewise, body temperature and blood pressure are in a constant state of change throughout the sleep phases. According to this principle, every person experiences regular ups and downs in his or her physical and mental performance even when awake during the light hours of the day. Here, for example, sleepiness around midday represents the ultradian rhythm change.
Diseases and ailments
Mania and depression are in a two-day alternating rhythm in many bipolar-impaired people, research has shown. Similar ratios are thought to occur in patients with schizophrenia. In these cases, the release of the chemical dopamine is out of balance. Under normal conditions, dopamine regulates a four-hour ultradian rhythm. The organism is accustomed to this and has adjusted to it. However, if the rhythm generator dopamine gets out of whack, entire reaction chains and physiological processes can suddenly change. The four-hour ultradian period then sometimes jumps to a rhythm of 48 hours, for example. Causes for these abrupt swings can be minimal switch settings in the genetic control mechanism of humans. Influences from the environment or from medications are often responsible for changes of this kind. They are perceived by the body’s dopamine-dependent rhythm generator and translated into biochemical clock changes.These in turn influence a wide variety of psychological disorders, but also, for example, the habitual sleep rhythm. Chronobiology, a relatively young branch of science, studies the temporal structuring and resulting behavioral patterns of organisms. It considers circadian, one-day periodic rhythms to be the most important in human physiology. However, it is increasingly clear that the shorter-term, ultradian rhythmicity is becoming more significant specifically for human health. Due to the sharp increase in the use of psychotropic drugs and the growing number of mental impairments or diseases, ultradian rhythmicity in particular is facing many difficulties. The lifestyle and the view of life are developing to an increasing degree diametrically to the so-called biological clock, which is given to man for his existence. This clock is built of all three rhythms (ultra-, circa- and infradian). The more a person neglects this, the greater his risk of disease becomes. For example, the increased lack of light of many people takes extremely negative influence on a healthy physiology. Chronobiology also clearly points out that too many trips across different time zones are detrimental to the human biorhythm in the long term. If more and more regularity is lost in daily life, for example by neglecting habitual eating times and adequate sleeping times, physical and mental strength inevitably decline.
