Rhythms, rhythmicity and aggression.

The relationships between biological rhythms and human aggressive behavior are addressed and discussed in this article: First, circadian rhythms and aggression are considered. Studies of sleep/waking cycle disturbances in aggression are reported. Severe aggression is associated with profound changes in sleep architecture. Causal link is difficult to establish given that sleep disturbance and aggressive behavior could be the symptoms of the same disorder. Specific aggressive behavior developed during sleep is also described. In addition, hormonal circadian rhythm studies are reported. Thus, low cortisol levels, in particular low cortisol variability, are associated with aggressive behavior, suggesting an inhibitory role of cortisol. Testosterone has daily and seasonal fluctuations, but no link with aggression has been established. Neurophysiological underlying mechanisms are discussed in the last part of this article, with a focus on the relationship between brain rhythm and aggression. Increase of slow-wave EEG activities is observed in individuals with aggressive behavior. Epilepsy, as a disease of brain rhythm could be associated with aggressive behavior, in pre, post and inter ictal periodes. Incidence of aggression is not likely more prevalent in epileptic individuals compared to those with other neurological conditions. Ictal changes take the form of profound behavioral changes, including aggressive behavior which has been interpreted as the emergence of "archeical" or innate motor patterns. In this multidisciplinary approach, the main difficulty is the categorization of the differents types of aggression. Finally, taken together, these studies suggest that biological rhythms, especially circadian rhythms, could provide therapeutic benefits to human aggressive behavior. Biological rhythymicity seems to be a necessary permanent training offering interesting perspectives for the adaptation to changes in the field of aggression.