BRAIN ASYMMETRY AND AGGRESSION

Relationship between Brain Asymmetry and Affect Regulation and Aggression

Relationship between Brain Asymmetry and Affect Regulation and Aggression

Chapter IV: Results & Discussion

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 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, therefore, suggest the existence of a certain correlation between brain asymmetries and human aggression.

History shows that humanity has the ability to allocate resources on several levels for starting and supporting wars. At present, western societies are living a moment of important terrorist pressure. The Basque terrorism in our own country (Ramirez & Sullivan, 1987) and the international terrorism on the Twin Towers in New York in 2001 and, more recently, on trains in Madrid and London, are only a few unfortunate examples of this fact. On the other side, newspapers report too often about fighting on the streets or domestic violence. All these actions refer to an unchained aggression with which we must daily coexist. It is important to emphasize that aggression refers to a specific behavior, namely a reaction to a situation, stimuli or particular emotion. According to these life circumstances, it seems logical to suppose that aggression is present in human nature and, consequently, about a possible existence of relationships between human brain and aggression. Moreover, since the scientific literature indicates existence of brain asymmetries and laterality functioning (see: Fox, 1991), one could wonder whether there was any relation between these and aggression.

Fig. 1. Experimental Stimuli and Paradigm. (a) Patients with brain asymmetry and control subjects were trained in the recognition of five visual patterns. Patterns were presented in random order and subjects responded with an identification key press (see text). (b) Stimulus presentation was followed—after a variable stimulus-to-mask onset asynchrony (SOA)—by a mask stimulus. (c) The temporal sequence of events.

Our argument in favor of a possible relation between brain asymmetries and human aggression is based on three ...