Cortisol, a index of hypothalamic-pituitary-adrenal (HPA) axis arousal, affects limbic structures and the autonomic nervous system (Raine, 1993). Cortisol levels have shown positive relationships with shyness and withdrawal (Kagan, Reznick, & Snidman, 1977), and also with anxiety, depression, and introversion (Dabbs & Hopper, 1990). Dabbs, Jukovich, and Frady (1991) suspect that cortisol will thereby inhibit violence through social withdrawal and depression.
A number of aggression-based studies have reported a relationship between depleted cortisol levels in habitual violent offenders (Virkkunen, 1985), adolescents with conduct disorder (Susman, Dorn, & Chrousos, 1991; Lahey & McBurnett, 1992), and in aggressive schoolchildren (Tennes & Kreye, 1985). A three-city longitudinal study (Lahey, Loeber, Stouthamer-Loeber, Christ, Green, Russo, Frick, & Dulcan, 1990; McBurnett, Lahey, Frick, Risch, Loeber, Hart, Christ, & Hanson, 1991; Walker, Lahey, Russo, Frick, Christ, McBurnett, Loeber, Stouthamer-Loeber, & Green, 1991) investigated the relationships between aggressive conduct disorder, anxiety, and cortisol levels. Aggressive non-anxious conduct disorder subjects proved to have markedly lower cortisol levels than their anxious conduct disorder counterparts. It would appear that cortisol levels are predictive of violent aggressive behavior in subjects with conduct disorder, where those subjects with higher levels are prone towards an anxious non-violent state rather than an non- anxious aggressive one.
Cortisol itself seems to have a mediating effect on other aggression related biochemicals. Dabbs, Jurkovic, and Frady (1991) investigated salivary testosterone and cortisol in incarcerated male offenders. As the previous testosterone studies would predict, a significant positive relationship was found between aggression and testosterone levels. While there was no main effect between cortisol and aggression in this study, there was a significant interaction between cortisol, testosterone, and aggression. Cortisol appears to act as a moderator between testosterone and violence, where high levels of cortisol inhibit testosterone levels and thereby inhibit aggression. Studies investigating alcoho- related aggression also found a similar testosterone-cortisol relationship. Lindman, Pahlen, Ost, and Ericksson (1992) found significantly different testosterone-cortisol levels with subjects who had committed a violent act while intoxicated versus their won testosterone-cortisol levels while sober. Cortisol levels were significantly lower, while testosterone levels were significantly higher, when the men were intoxicated. Apparently the fluctuation in levels while intoxicated eliminated the cortisol related aggression inhibition factors. The evidence is clear. Biochemistry is related to aggressive behavior. It would appear that testosterone is the primary biochemical factor, while cortisol is a mediator of testosterone levels that inhibits aggressive behavior. However, the idea that these biochemicals are the lone causal factors behind aggression is unlikely. Recent neurochemical research has suggested that the physiological correlates of aggressive behavior may be far more complex.
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