Primate models to understand human aggression.

Although primate studies have yielded models of aggressive behaviors that clinicians encounter in their clinical practice, further studies need to be performed to establish insights into the biological mechanisms that underlie these behaviors. Nonetheless, studies of aggression in rhesus monkeys point to 2 chief categories of aggression--defensive and offensive--and suggest differing underlying neural mechanisms for these types of behaviors. Defensive aggression is fear motivated and related to extreme asymmetric right frontal activity in the brain and high plasma cortisol concentrations. On the other hand, offensive and/or impulsive aggression is associated with low serotonergic activity in the central nervous system, high levels of testosterone, and lower levels of cortisol. Moreover, all forms of aggression in rhesus monkeys appear to be modulated by environmental factors, and marked disruptions to the mother-infant relationship likely confer increased risk.