Neural mechanisms of aggression

REVIEWS

Aggression is a complex social behaviour that evolved in the context of defending or obtaining resources1.

Although some features of aggression are species-specific, there are broad similarities across species (BOX 1).

Neurobiological experiments show that many of the same neurochemical and anatomical systems are activated during aggressive behaviour in humans and non-human animals, even though the specific behavioural outputs can differ greatly. This Review takes a bottom-up approach to assess how genes and the environment contribute to the functioning of neural mechanisms of aggression. We discuss new data on molecules that are associated with aggression and that have been revealed by pharmacological and gene-targeting techniques, primarily in rodents. We will also examine the neuroanatomical organization of aggression in several contexts. This Review will show that the complex nature of aggressive behaviour necessitates a comprehensive approach that considers both genetic and environmental factors.

Aggressive behaviour

Traditionally, aggression has been defined as overt behaviour that has the intention of inflicting physical damage on another individual2, and the potential for aggressive behaviour exists whenever the interests of two or more individuals conflict. Although aggression can yield competitive advantages, it is time-consuming and can be dangerous. When it is exaggerated, persistent or expressed out of context, it can be considered pathological. Psychiatrists and other care providers are particularly vulnerable to the serious consequences of violent outbursts in their patients, and an overarching goal of research into aggression is to develop interventions that can reduce maladaptive

or pathological aggressive behaviour. In many cases, these interventions must be specifically tailored because of the patients vulnerability, especially in the case of aggressive children or geriatric patients. To understand the mechanisms that underlie aggression, we need more precision in reporting the antecedents and consequences of different types of aggression3. From an ethological perspective, aggression is used for obtaining or defending food or mates from competitors; from a psychiatric perspective, it is thought to be motivated by hypothetical constructs such as anger, irritation, frustration, fear and, in some cases, pleasure4.

Two subtypes of aggression have been identified in humans: the controlledinstrumental subtype and the reactiveimpulsive subtype5. Reactive aggression is considered to be more impulsive (it is usually associated with anger), whereas instrumental aggression is considered to be more purposeful and goal-oriented. The instigation...