Human circadian rhythms. Synchronization and dyschronism

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 24 h 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.