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Abstract
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There has been much interest in the role of serotonin in aggressive behavior during the past two decades, but no simple one-to-one causal relationship has been found between this biological variable and aggression. The influence of serotonin is best analyzed within a broader framework that includes consideration of its role in the inhibition of impulses, the regulation of emotions and social functioning, domains that are closely linked to aggression. Impulsivity and strong emotional states often accompany violent acts. Aggressive individuals are likely to experience general difficulties with impulse control and emotional regulation, and they show impaired social cognition and affiliation. Serotonergic dysfunction will influence aggression differently, depending on the individual's impulse control, emotional regulation, and social abilities. Yet, aggressive acts occur in a broader social context. As such, serotonergic function has an effect not only on the individual but also on the group dynamics, and it is in turn influenced by these dynamics. Whether aggression will occur when serotonin dysfunction is present will depend on individual differences as well as the overall social context.
There has been a great deal of interest concerning the role of central nervous system (CNS) serotonin in aggression. Findings in various areas, including human and animal studies, pharmacological, imaging, and receptor subtyping research indicate the importance of serotonin in certain types of aggressive behaviors. The literature reviewed in this article is pertinent in understanding the relationship between serotonin and aggressive behavior in the context of three important domains related to aggression, namely impulse control, affect regulation, and social functioning.
Extensive literature dating back to the 1960s provides evidence of an association between animal aggression and reduced serotonergic function. Beginning in the late 1970s, studies focused on human aggression, examining violence toward others as well as suicide, which was viewed as a form of violence, i.e., self-directed violence. Serotonergic function was a marker and predictor of both violence and suicide in various populations. However, not all aggressive behaviors were associated with decreased serotonin function and this association needed further characterization. These aggressive behaviors were often maladaptive in some ways, whether impulsive, emotionally driven, or socially dysfunctional. Impulse control, emotional regulation, and social functioning appear to be important qualifiers of the violent behavior associated with serotonin dysfunction. They also serve to characterize further the overall functioning of the violent individuals whose difficulties are rarely limited to aggression alone.
Of these three areas, impulsivity has received the most attention. Serotonin is seen as playing a role in the inhibition of impulses other than aggressive ones. Researchers have investigated the relationship of serotonin to various impulsive behaviors and to "impulsivity" as a trait. The regulation of emotions is relevant to both violence and impulse control. Strong emotional states often accompany violent acts that are considered impulsive. Irritability, temper outbursts, or a greater emotional responsiveness to others are often present in violent or impulsive individuals. Many of these individuals have general problems with emotional self-regulation.
Social functioning is linked to violence in many ways. An aggressive individual is more likely to show various social problems, including impaired social cognition and social affiliation. Dysfunctional aggressive behavior can be viewed as representing one extreme along a continuum of social interactions; the opposite pole consisting of skilled affiliative behaviors and social cooperativeness. However, it is important not to limit the analysis to the person's social characteristics. Aggressive acts occur in a social context. The same characteristics can lead to dissimilar behavioral outcomes, depending on the attributes of other group members. The channeling of impulses and emotions are expressed in a social context and are the products of social interactions. Viewed in this fashion, aggression is a complex phenomenon that must be analyzed at the biological, psychological, and social levels of organization. Basic structures and processes at one level help define the other levels. |