Brain Mechanisms

There are other experimental data indicating that the septum modulates offensive behaviors in various muroid rodents. In the mouse (Slotnick & McMullen 1972) and rat (Lau & Miczek 1977; Blanchard et al. 1977), septal lesions reduce offense behavior. In the hamster, septal lesions increase offense (Sodetz & Bunnell 1970; Johnson et al. 1972), and septal stimulation inhibits it (Potegal et al. 1978). The functional significance of these effects is not known. By analogy with its role in submission and defense, one might expect the septum to process information indicating that the opponent was a conspecific, which might be expected to facilitate offense. Another possibility is that septal activation reflects familiarity or lack of familiarity with the test environment. The septum receives a major input from the hippocampus, which has been implicated in the process of spatial recognition (Q'Keefe & Nadel 1978). This may be important for offense, since offense is more readily exhibited by an animal when it knows that it is in a familiar "home" environment or territory (Adams 1976).

The motivating stimuli for competitive fighting are probably processed in the amygdala and hypothalamus. Miczek et al. (1974) have found that lesions of the cortical amygdala, periamygdaloid cortex, and stria terminalis abolish fighting in rats during food competition. These data are supplemented by findings that amygdaloid lesions in the rat reduce "incentive motivation" (Gaston 1978) and reduce the "frustration effect" of non-reward in a feeding situation (Henke 1973). There are reports that ventromedial hypothalamic lesions (Grossman 1972) and knife cuts between the ventromedial and anterior hypothalamus (Grossman & Grossman 1970) abolish competitive fighting in female rats. A thesis in our laboratory (Severini 1973) found that anterior hypothalamic lesions abolished the competitive fighting, but that ventromedial hypothalamic lesions did not. These contradictory findings indicate that further research is needed on the role of the hypothalamus in competitive fighting.

The neural mechanisms of offense are outlined in Figure 4. The motivating stimuli for offense are shown as activating a number of forebrain nuclei, with unfamiliar conspecific stimuli activating the amygdala and septum, male odors activating the olfactory tubercle (in males), and the stimuli of competitive fighting activating the amygdala. These influences are shown as converging upon a pathway that runs in the lateral hypothalamus from the preoptic hypothalamus caudally and into the midbrain to an offense motivational mechanism.

Motor patterning mechanisms and releasing and directing stimuli for offense. The motor patterning mechanisms for offense are similar in the rat and cat. In the rat and other muroid rodents they consist of approach locomotion, offensive sideways posture, offensive upright posture, and the bite-and-kick attack (Lehman & Adams 1977). In the cat they consist of approach, a straight-backed sideways posture, and a biting attack (Leyhausen 1956). In both cat and rat, offense is accompanied by piloerection. Both the sideways and upright offense postures in the rat are probably coordinated by the same motor patterning mechanisms as the corresponding postures of offense (Lehman & Adams 1977). The neural mechanisms for the offense motor patterns of the cat and rat have not been specifically studied. However, if it is true that the patterning mechanism for offensive upright posture is the same as that for defensive upright posture, then the same releasing and directing stimuli would be involved. As mentioned earlier, these have been studied in our laboratory (Kanki & Adams 1978). The releasing and directing stimuli for the other offense motor patterns have not been specifically studied. It would appear from casual observations that most of the motor patterns require visual releasing and directing stimuli, since they can occur at distances from the opponent that are beyond the reach of tactile communication.

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