Vol 5 n° 4 - Chronobiology and Mood Disorders
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he rhythmic (as opposed to linear) expression of biological variables and the temporal organization of these rhythms  represent  an  adaptation  of  organisms  to  the rhythmic changes in the external environment. Periodic oscillations (rhythms) have been documented in biologi- cal variables in a whole spectrum of living organisms (from unicellular to multicellular).1,2 However, this phenomenon is not merely a reaction to environmental changes; it is generally held that the rhythms are governed by an active system capable of self-sustained oscillations (endogenous rhythms).1 Consequently, the shape of rhythms and the S t a t e   o f   t h e   a r t 3 2 7 Copyright © 2003 LLS SAS.  All rights reserved www.dialogues-cns.org Concepts in human biological rhythms Alain Reinberg, MD, PhD; Israel Ashkenazi, PhD Keywords:   biological   rhythm;   temporal   organization;   de synchronization; allochronism; dyschronism; shift work; affective disorder Author  affiliations: Unité de  Chronobiologie, Fondation Adolphe de Rothschild,  Paris,  France  (Alain  Reinberg);  Department  of  Human  Genetics and Molecular Medicine, School of Medicine, Tel Aviv University, Ramat Aviv, Israel Address  for  correspondence:  Alain  Reinberg,  Unité  de  Chronobiologie, Fondation Adolphe de Rothschild, 29 rue Manin, 75940 Paris Cedex 19, France (e-mail: areinberg@wanadoo.fr) T Biological rhythms and their temporal organization are adaptive phenomena to periodic changes in environmen- tal factors linked to the earth’s rotation on its axis and around the sun. Experimental data from the plant and ani- mal kingdoms have led to many models and concepts related to biological clocks that help describe and understand the mechanisms of these changes. Many of the prevailing concepts apply to all organisms, but most of the experi- mental data are insufficient to explain the dynamics of human biological clocks. This review presents phenomena that are mainly characteristic of—and unique to—human chronobiology, and which cannot be fully explained by concepts and models drawn from laboratory experiments. We deal with the functional advantages of the human temporal organization and the problem of desynchronization, with special reference to the period (t) of the circa- dian rhythm and its interindividual and intraindividual variability. We describe the differences between right- and left-hand  rhythms  suggesting  the  existence  of  different  biological  clocks  in  the  right  and  left  cortices. Desynchronization of rhythms is rather frequent (one example is night shift workers). In some individuals, desyn- chronization causes no clinical symptoms and we propose the concept of “allochronism” to designate a variant of the human temporal organization with no pathological implications. We restrict the term “dyschronism” to changes or alterations in temporal organization associated with a set of symptoms similar to those observed in subjects intol- erant to shift work, eg, persisting fatigue and mood and sleep alterations. Many diseases involve chronic depriva- tion of sleep at night and constitute conditions mimicking that of night shift workers who are intolerant to desyn- chronization. We also present a genetic model (the dian-circadian model) to explain interindividual differences in the period of biological rhythms in certain conditions. © 2003, LLS SAS Dialogues Clin Neurosci. 2003;5:327-342.