Brain Mechanisms

There are many parallels in the neural circuitry of offense, defense, and submission. These may be seen in the composite diagram of the neural circuits presented in Figure 5. All three involve forebrain pathways that process motivating stimuli in the septum and amygdala convey these influences to the hypothalamus, and then relay them caudally to motivational mechanisms in the midbrain. The motivational mechanisms with known locations are in the central gray of the midbrain, and the other motivational mechanism (offense) may he there as well. From the central gray, descending projections fan out to motor patterning mechanisms; although their exact locations are not known, most are presumed to lie in the midbrain and hindbrain, since most motor patterns can be obtained in decerebrate animals. Releasing and directing stimuli may require forebrain pathways, however.

Offense, defense, and submission may be differentiated by appropriate brain lesions, despite their many parallels. Offense and defense may be differentiated by hypothalamic lesions that, if very extensive, can abolish offense while enhancing defense (Adams 1971). Defense and submission can be separated by lesions of the medial hypothalamus or amygdala; the former enhance defense and abolish submission, while the latter have an opposite effect.

Whereas previous classifications of aggressive behavior have been based upon logical distinctions made by the observer, the present classification is based ultimately upon the neural circuitry involved. This leads to differences in the conclusions reached. In particular, the present conclusions may be compared to three previous classifications based upon stimulus situations eliciting aggression (Moyer 1968), response patterns of aggression (Flynn 1976), and a functiona1 classification of aggression (Wilson 1975).

Offense, according to the present analysis, consists of behavior under the control of an offense motivational system. In cats and rats this system is activated by several types of motivating stimuli processed by the amygdala and, perhaps, the preoptic hypothalamus: olfactory stimuli that characterize male conspecifics (in males only); olfactory and other stimuli that characterize the opponent as unfamiliar; and/stimuli associated with competition for food or water when the animal is food- or water-deprived. The motor patterns of offense include approach and chase, bite-and-kick attack, sideways postures, piloerection, and (in the rat) an offensive upright posture. In the classification system of Moyer (1968) offense subsumes inter-male aggression, territorial defense, that portion of irritable aggression elicited by competitive interactions, and that portion of maternal aggression that involves such motor patterns as bite-and-kick or sideways postures. In the classification system of Flynn (1976) it corresponds to offensive threat, and (perhaps) to certain quiet attacks that might take place in intraspecific encounters. In the classification system of Wilson (1975) it corresponds to territorial aggression and dominance aggression.

Defense and submission, according to the present analysis, consist of behaviors under the control of defense and submission motivational systems. In cats and rats the motivating stimuli of these two systems are the same, involving a forebrain pathway through the "defense zone" of the amygdala and perifornical hypothalamus, which may convey olfactory motivating stimuli, and ascending pathways, which convey pain, dorsal tactile stimulation, sudden noise, or visual movement. There is considerable overlap in the output motor patterns, including upright and sideways postures, squealing and hissing, freezing, and fleeing. There are also differences, however, with lunge-and-bite attack and striking (in the cat) shown only during defense, and submissive postures and ultrasound (in the rat) shown only during submission. The animal normally shows defense against unknown opponents, but if its consociate modulator is activated by stimuli of a known conspecific or other life-long associate, then the behavioral control is shifted from the defense to the submission motivational system.

Defense and submission have not been differentiated by previous authors. In the classification of Moyer (1968) they subsume the categories of fear-induced aggression, that portion of irritable aggression elicited by pain, and a part of maternal aggression that involve a lunge-and-bite attack. In the classification of Flynn (1976), defensive threat and attack are corresponding categories. And in the classification of Wilson (1975) they include the category of antipredatory aggression.

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