Aggression is controlled in large part by the area in the older part of the brain known as the amygdala (Figure 9.5). The amygdala is a brain region responsible for regulating our perceptions of, and reactions to, aggression and fear. The amygdala has connections with other body systems related to fear, including the sympathetic nervous system, facial responses, the processing of smells, and the release of neurotransmitters related to stress and aggression.
In addition to helping us experience fear, the amygdala also helps us learn from situations that create fear. The amygdala is activated in response to positive outcomes but also to negative ones, and particularly to stimuli that we see as threatening and fear arousing. When we experience events that are dangerous, the amygdala stimulates the brain to remember the details of the situation so that we learn to avoid it in the future. The amygdala is activated when we look at facial expressions of other people experiencing fear or when we are exposed to members of racial outgroups (Morris, Frith, Perrett, & Rowland, 1996; Phelps et al., 2000).
Although the amygdala helps us perceive and respond to danger, and this may lead us to aggress, other parts of the brain serve to control and inhibit our aggressive tendencies. One mechanism that helps us control our negative emotions and aggression is a neural connection between the amygdala and regions of the prefrontal cortex (Gibson, 2002).
The prefrontal cortex is in effect a control center for aggression: when it is more highly activated, we are more able to control our aggressive impulses. Research has found that the cerebral cortex is less active in murderers and death row inmates, suggesting that violent crime may be caused at least in part by a failure or reduced ability to regulate emotions (Davidson, Jackson, & Kalin, 2000; Davidson, Putnam, & Larson, 2000).