[Synchronization and dyschronism of human circadian rhythms].

Properties of biological rhythms are presented briefly as well as the conventional model dealing with the synchronizing effects of the day/night (or Light/Dark) alternation on the suprachiasmatic nuclei (SCN) the master-clock, which is supposed to control all our rhythms. However, apart from the SCN role, a set of experimental arguments supports the existence of biological clocks in the brain cortex. The synchronization of the latter (resetting them and making their period = 24 h) may be achieved not only by the periodicity of physical Light/Dark signals but also by the periodicity of social signals involving perceptions with eyes, ears, nose and skin. Distribution of peaks and troughs of biological rhythms in the 24h scale reveals the organism's temporal order. Its alteration (dyschronism) results from a phase shift and/or a change in the period length of a rhythm with regard to the others. In human beings, dyschronism is a trivial phenomenon. It appears even if synchronizers are present, with interindividual differences. It is likely that dyschronism induces a set of symptoms in sensitive subjects, prone to react to it.