EVidence for dorsolateral and orbital prefrontal cortical involvement in the expression of aggressive behavior

Numerous studies have implicated the role of the prefrontal cortex in the expression of aggressive behavior. However, the nature of this relationship remains poorly understood. As such, the purpose of this article is to review both the animal and human literature pertaining to prefrontal cortical functioning and aggression in an attempt to help clarify this relationship. Particular attention is paid to differentiating the functions of the dorsolateral and the orbital regions of the prefrontal cortex in the expression of aggression. Evidence was garnered from four different types of studies: 1) those examining aggressive behavior in animals following ablations to the prefrontal cortex; 2) those examining aggressive behavior in humans following surgical and accidental lesions to the prefrontal cortex; 3) those examining prefrontal cortical functioning in individuals with psychiatric disorders characterized by aggression; and 4) those relating prefrontal cortical functioning to human aggressive behavior in laboratory situations. The general conclusion of this article is that the dorsolateral region of the prefrontal cortex is more likely to be involved in the expression of physical aggression whereas the orbital region is more likely to be involved in the expression of what is termed herein “disinhibited-nonaggressive” behavior. © 1995 Wiley-Liss, Inc.     

Variation in aggressive behavior and anatomo-physiological correlates generated by crowding without physical contact in the house mouse

Behavioral, physiological (i.e., endocrine), and anatomical consequences of crowding in mice were studied in a situation where animals were in auditory, visual, olfactory, and tactile contact but restrained from full physical interactions, to prevent overt aggression. Males that cohabited with females undisturbed by neighboring conspecifics showed greater propensity to attack same-sex intruders and had higher plasma testosterone levels than did their “crowded” counterparts, that is, males cohabiting with females and housed adjacent to other male/female pairs. In this respect, the latter animals resembled submissive males. However, a significant increase in weight of androgen-dependent target organs (i.e., seminal vesicles and preputial glands) was found in crowded males. These data indicate that despite the observed inhibition of social aggression these males are not physiologically comparable (homologous) to male mice that experienced defeat and the stress of submission during fighting. The intriguing possibility that different conversion pathway of testosterone are accelerated, as a result of social communication, in males living in these two environments and the behavioral implications of these possibilities are discussed. Finally, the parental behavior of crowded animals, although not freely interacting with each other, was disrupted, causing a marked decrease in reproductive success. In this situation a high incidence of infanticide of their offspring by both parents was observed, whereas this behavior was virtually absent in non-crowded male/female pairs.     

Testosterone intake and aggressiveness: Real effect or anticipation?

In a double-blind experiment, human males (n = 27) were given either testosterone (40 mg/day), placebo, or no treatment, over a one week period. Subjective and observer assessed mood estimations were conducted before and after treatment. Testosterone levels in saliva were measured with radioimmunoassay. The results revealed a significant placebo effect [c. f. Medicine and Science in Sports 4: 124–126]: After treatment, the placebo group scored higher than both the testosterone and the control group on self-estimated anger, irritation, impulsivity, and frustration. Observer-estimated mood yielded similar results. The lack of a placebo effect in the testosterone group is intriguing, and may be due to secondary effects caused by suppression of the body's own testosterone production, since recorded non-protein bound testosterone did not significantly rise due to treatment. The resultss suggest that androgen usage causes expectations, rather than an actual increase of aggressiveness. © 1994 Wiley-Liss, Inc.     

Evidence for a motor mechanism of pain-induced aggression instigation in humans

The automatic skeletal motor responses of 20 male and 20 female student subjects (aged 20–36) receiving a painful stimulation (electric shock) were studied by examining voluntary concomitant extensions and flexions of the arm. These movements were either of long duration, allowing for an on-line control of their execution or, of short duration, requiring extensive pre-programming. Subjects were instructed either to push or to pull a lever upon receipt of an acoustic signal, which was paired or unpaired with an electric shock. Latencies for long duration movements (regardless of direction) were reduced by reception of painful stimulation. Latencies of short duration extensions and flexions were respectively reduced and increased by painful stimulation. Latencies of short duration movements were larger for females than males, regardless of movement direction. These data suggest that painful stimulation elicits automatic movements which affect programming of the termination of simultaneous voluntary movements. Implications of these findings for the study of aggressive behavior are discussed. © 1994 Wiley-Liss, Inc.     

Fighting experiences and natural killer cell activity in male laboratory mice

There is currently much interest in the potential impact of psychological factors on immune responses. An attempt was made to assess the effects of dominant/subordinate polarity in male mice on the cytotoxic activities of their natural-killer (NK) cells. On the basis of repeated agonistic encounters, categories of subordinate and dominat animals were selected. These animals were compared with manipulated controls (introduced to a novel test cage without an opponent on each occasion) and undisturbed controls (who remained in isolation without manipulation). In terms of NK activity, immunosuppression was observed in both dominant and subordinate categories when compared to undisturbed controls. There were, however, no differences between the fighting exposed subjects and the manipulated controls, suggesting that stress accounts for any changes. © 1994 Wiley-Liss, Inc.     

Anger and aggression in women: Influence of sports choice and testosterone administration

We report on two studies of anger and aggression in women. One study concerns an experimental study of anger induction in aggressive and non-aggressive sportswomen. It was found that sports choice in itself, contrary to expectation, does not predict anger arousal and aggressive behavior in the laboratory. However, at an individual level the anger proneness of the subject, as measured by a questionnaire we developed, was related to the intensity of aggressive behavior and subjectively reported anger. The second study concerns the activating effects of androgens on aggression and anger proneness. In a group of 22 female-to-male transsexuals, a battery of anger proneness and aggression questionnaires was administered twice: shortly before and 3 months after the start of androgen treatment. Administration of androgens was clearly associated with an increaese in anger proneness, although there were no changes in several aspects of overt aggressive behavior. © 1994 Wiley-Liss, Inc.     

Influence of timing of post-weaning isolation on play fighting and serious aggression in the male golden hamster (Mesocricetus auratus)

Effects of timing of social isolation on play fighting and serious fighting were studied at different ages in male golden hamsters. Litters were isolated at 21, 35, and 65 days of age, and tested in a resident-intruder paradigm. Behaviors were compared within grous and with a fourth group of socially reared conspecifics. The earlier the pups were isolated, the more they engaged in play activities. Later, in adulthood, the aggression level of the same animals was retested using the same paradigm. The three isolated groups showed a high level of aggression, with significant differences among them. When compared with socially reared subjects, a reliable difference in the level of aggression was also found. These results support the view that early social experience is important, suggesting that isolation during early critical periods of socialization has a significant impact on play fighting, whereas short periods of isolation may be enough to trigger adult agonistic behavior. © 1994 Wiley-Liss, Inc.     

Hostile masculinity,sexual aggresion,and gender-biased domineeringness in conversations

This study assessed the ability of certain variables to predict which men would be more domineering in conversations with a woman and/or with a man. The variables included men's self-reported sexually aggressive behavior and several components comprising a personality profile labeled “Hostile Masculinity.” As expected, these variables successfully predicted domineering behavior toward the female but not toward the male. These findings supported theories hypothesizing that men's desire to control women and men's antisocial behavior toward them are due to specific rather than to general factors (i. e., evolutionary and feminist theorizing). © 1994 Wiley-Liss, Inc.     

Defensive reactions of “wild-type” and “Domesticated” wild rats to approach and contact by a threat stimulus

Selective breeding of wild rats over many generations on the basis of low or high defensive threat and attack to human approach and contact has produced highly polarized “domesticated” and “wild-type” animals. Because the selection procedure selectively involves these two defense patterns, and these clearly differ in the two groups, it is of interest to determine if other, nonselected, defensive behaviors to threat stimuli also change. “Domesticated” and “wild-type” rats of the thirty-fifth generation were run in a fear defense test battery (F/DTB) to systematically evaluate defensive behaviors to a variety of present threat stimuli. “Domesticated” rats showed reduced avoidance and slower flight speed to an approaching experimenter, reduced jump/startle response to handelap and dorsal contact, less vocalization and boxing to vibrissae stimulation or to an anesthetized conspecific, and reduced defensiveness to an attempted pickup by the experimenter. These results indicate that selective bi-directional breeding for defensive threat and attack to human approach and contact produces group differences in a variety of defensive behaviors, and in defensiveness to stimuli other than those on which the selection was based. © 1994 Wiley-Liss, Inc.     

Individual differences in the study of human aggression

Excessive concern for simplicity has often led us to underestimate the complexity of aggression. Over the years, several scales related to aggression have been identified and validated both on adults and on children. Ultimately, two main higher order dimensions, emotional responsivity and proneness to aggression, repeatedly emerged in a series of second-order factor analysis. These dimensions are rather similar to two of the big five factors of personality: neuroticism/emotinal stability and hostility/agreeableness, respectively. Several studies corroborate the plausibility of a higher level bidimensional conceptualization of aggression that, while preserving the heuristic validity of looking for more specific constructs of aggression, can link the field of aggression to the field of personality. © 1994 Wiley-Liss, Inc.