Researchers have examined the role of neurotransmitters in aggression in animals and humans, but they have been unable to identify a single cause. Findings reveal that sero-tonin plays a major inhibitory role in aggressive behavior; therefore, low serotonin levels may lead to increased aggressive behavior. This finding may be related to the anger attacks seen in some clients with depression. In addition, increased activity of dopamine and norepineph-rine in the brain is associated with increased impulsively violent behavior. Further, structural damage to the limbic system and the frontal and temporal lobes of the brain may alter the person’s ability to modulate aggression; this can lead to aggressive behavior (Siever, 2008).
Infants and toddlers express themselves loudly and intensely, which is normal for these stages of growth and development. Temper tantrums are a common response from toddlers whose wishes are not granted. As a child matures, he or she is expected to develop impulse control (the ability to delay gratification) and socially appropriate behavior. Positive relationships with parents, teachers, and peers; success in school; and the ability to be responsible for oneself foster development of these qualities. Children in dysfunctional families with poor parenting, children who receive inconsistent responses to their behavior, and children whose families are of lower socioeconomic status are at increased risk for failing to develop socially appro-priate behavior. This lack of development can result in a person who is impulsive, easily frustrated, and prone to aggressive behavior.
Leary, Twenge, and Quinlivan (2006) found a relation-ship between interpersonal rejection and aggression. Rejec-tion can lead to anger and aggression when that rejection causes the individual emotional pain or frustration, or is a threat to self-esteem. Aggressive behavior was often seen as a means of re-establishing control, improving mood, or achieving retribution.