Heteronomous Rhythms

Abstract

In all experiments discussed so far, human circadian rhythms were running autonomously (i.e., without environmental time cues). It was shown that environmental stimuli, indeed, are able to modify the rhythms, but this influencing did not break, even when effective in a self-control mode, the autonomy of the rhythms. In contrast to this, under natural conditions circadian rhythms are synchronized to the day-night cycle (i.e., to a period of exactly 24.0 hours). Two questions, therefore, arise; what is the mechanism of synchronization and what is the periodic environmental stimulus which is able to synchronize human circadian rhythms? To answer these questions, experiments must be performed where natural zeitgebers are excluded, as in experiments with autonomously running rhythms. Artificial zeitgebers then must be introduced which, in contrast to natural ones, can be manipulated experimentally regarding period, phase, and other parameters. In the first place, the question for the general effects of zeitgebers will be evaluated independently of the kind of zeitgeber that is effective.