Genetic and Neurobiological aspects of Anger and Aggressiveness.

To date, research on anger and human aggression is one of the most challenging fields for genetics and neurobiology. Nevertheless, its objects continue to be inconsistently defined and to generate incomplete theoretical models. Moreover, most studies on anger and its related constructs, such as aggression, impulsivity and violence, are generally based on specific samples (e.g. patients with personality disorders or violent offenders). Notwithstanding, twin and family studies suggest that some forms of human aggression, particularly irritable/impulsive aggression, may have substantial heritability. Gene-environment interactions are supposed to play a major role in the development of aggression and antisocial behaviors, in the sense that individuals with a biological risk for aggression may be particularly vulnerable to the effect of psychosocial adversity. For example, genes for the serotonin transporter and monoamine oxidase type A (MAO-A) may interact with childhood maltreatment and early adverse experiences to predispose to violence. Serotonin in particular is supposed to be an important factor in regulating aggressive-impulsive behaviors. Subjects with impulsive aggression were found to have reduced serotonin function in the orbitofrontal cortex and anterior cingulate cortex, considered as key areas regulating aggressive behaviors. This may lead to an imbalance between the “top-down” control provided by the orbital frontal cortex and anterior cingulate cortex, and excessive “bottom-up” triggered by limbic regions, such as the amygdala and insula. Functional magnetic resonance imaging (fMRI) studies also suggest that patients who often experience anger and aggression dyscontrol may be particularly sensitive to emotional provocation in the direction of aggression (e.g. faces with angry expressions). This chapter will focus on the neurobiological, genetic and neuro-psychological aspects of anger with the purpose to give a comprehensive, integrative theoretical model of this emotion and its correlates, aggression and impulsivity.