Psychiatric chrono-epidemiology: its relevance to the study of aggression

Chrono-epidemiology is the study of the distribution of health events according to time. The time intervals taken into account have cyclic patterns and include circadian, weekly, seasonal, and circannual rhythms. In the behavioural field, chrono-epidemiology can be and has been applied to studies concerning the causes of death (suicide and homicide), clinical events such as admissions to and contacts with mental healthcare services, and the seasonal distribution of crime involving the use of violence. Frequently reported findings include clear circadian and seasonal rhythms present in the phenomenon of suicide (rhythms more evident in the case of violent suicide); seasonal rhythms in the expression of aggression by patients hospitalised for mental illness; and a circannual recurrence of crimes with a violent component. The intrinsic circadian and seasonal rhythms of some neuronal systems, particularly those of serotonin, involved in the control of mood and impulses, are thought to favour the behavioural rhythms observed, although the contribution of socio-environmental factors, such as the fluctuation of supportive networks according to time, is also acknowledged. By demonstrating non-casual recurrence of certain behaviour and by exploring the socio-biological basis of the rhythms beneath these recurrences, chrono-epidemiology may offer important etiologic and preventive clues to the understanding of the biological and environmental correlates of aggressive behaviour.