Aggression and Brain Asymmetries: A Theoretical Review

Abstract

The relationship between aggression and brain asymmetries has not been studied enough. The association between both concepts can be approached from two different perspectives. One perspective points to brain asymmetries underlying the emotion of anger and consequently aggression in normal people. Another one is concerned with the existence of brain asymmetries in aggressive people (e.g., in the case of suicides or psychopathies). Research on emotional processing points out the confusion between emotional valence (positive-negative) and motivational direction (approach-withdrawal). Because of this, it is not clear whether the frontal asymmetry reflects the valence of the emotion, the direction of the motivation, or a combination of valence and motivation. Appetitive motivations are not always associated with positive affects. Anger (a negative emotion) has been associated with approach motivation and with aggression. Relative left-prefrontal activity is associated with state anger and with aggression. This information would lead to the conclusion that the more violent a culture, the higher the relative proportion of the right-handers. On the other side, there is an exaggerated structural asymmetry in the anterior hippocampus (R>L) in unsuccessful psychopaths. In suicidal persons, the functional insufficiency of the right hemisphere produces a compensatory shift to left hemisphere information processing, showing a reversed asymmetry of typical traits for suicidal people. These findings suggest, therefore, the existence of a certain correlation between brain asymmetries and human aggression.