Interestingly, low levels of 5HT are related to what is called “impulsive aggression” in monkeys, but not to “planful aggression” (Frankle et al., 2005). Aggressive monkeys who use their aggression well, and thus end up at the top of the group hierarchy, do not have lower 5HT levels. Aggressive monkeys who use aggression in ill-advised, unsuccessful ways and who also have other poor social skills, do have lower 5HT levels. Animal researchers have demonstrated that the PFC brain region shows a high concentration of 5HT receptors in monkeys whose behavior is socially adapted, and low 5HT receptor levels in aggressive, socially uncooperative animals (Raleigh & Brammer, 1993). Frankle et al. (2005) found that low 5HT, particularly in the ACC, is associated with “impulsive aggression” and impaired regulation of negative emotions. In addition, selective 5HT reuptake inhibitors, which serve to increase overall levels of 5HT in the synaptic cleft, have been very effective in regulating emotion, decreasing depression (Arroll et al., 2005) and reducing risky behaviors in a variety of clinical disorders, including borderline personality disorder (Barbe, Rubovsky, Venturini-Andreoli, & Andreoli, 2005).
