Brain Mechanisms

Changing methodology in aggression research. David Adams provides a long overdue review of recent research on the neurophysiology of agonistic behaviour. However, to simply refer to this work as "a review" does not do justice to the conceptual framework within which research findings are presented. The author has adopted a "neuroethological" approach to the problem and, as such, has placed considerable emphasis upon thorough behavioural analysis. This awareness of the value of ethological methodology has not been a characteristic feature of neurophysiological/ psychopharmacological investigations of agonistic behaviour over the years.

Scott (1966), in pointing out that "aggression is a poor scientific term," suggested that fighting behaviour cannot be fully analyzed without also studying the alternative patterns of escape, threat, "freezing," defensive posture, dominance, and subordination. To cover this behavioural system, composed of behavioural patterns having the common functions of adaptation to situations involving physical conflict between members of the same species, he coined the term "agonistic behaviour." His own studies and those of Grant and Mackintosh (1963) provide detailed accounts of the social postures of the most commonly used laboratory animals: rats and mice. Unfortunately, the significance of these contributions has largely been ignored, with most research relying heavily upon rather simplistic (and perhaps somewhat dubious) models of "aggression." However. within the past five years, several dominant trends have become apparent in the literature, which indicate that methodology in aggression research is undergoing a metamorphosis. I believe that these trends may be summarized as follows:

1. The development of more "naturalistic" test paradigms This approach, exemplified by the work of Blanchard's [q.v.] group on colony reaction to intruders (Blanchard et al 1975; Blanchard and Blanchard 1977; Blanchard, Takahashi, and Blanchard 1977; and Blanchard et al. 1977c) and Miczek's [q.v.] group on fighting generated by frustrative nonreward (Miczek 1974; Miczek and Barry 1974; 1977) facilitates the detailed observation of the effects of physiological/ pharmacological manipulation on the full repertoire of agonistic response patterns in rats.

2 The recognition of differential behavioural effects of manipulation, depending upon the status of the treated animal. Miczek (1974) has shown quite different effects of amphetamine given to dominant or subordinate animals: In the former, low doses of the drug enhance all elements of attack, whilst in the latter, drug treatment results in exaggerated defensive and submissive postures.

3. The realization that the behaviour of an untreated animal may alter in the presence of a treated animal: Early work by Krsiak and Steinberg (1969) showed changes in the social behaviour of undrugged rats in the presence of chlorpromazine-treated rats. More recently Miczek (1974) has reported that subordinate animals, under the influence of amphetamine, provoke more attacks and threats from undrugged dominants.

Recent research, through the application of this methodology, has highlighted the fallibility of some "established facts" in aggression literature. The minor tranquilizer, chlordiazepoxide, long thought to reduce aggression, has recently been shown to dramatically increase attack and threat in rats (Miczek 1974). Factors such as drug dose, status of the injected animals, and the test paradigm appear to be critical determinants of behavioural response. Septal lesions, often reported to induce "hyperaggressivity," have recently been found to reduce elements of attack in both colony (Blanchard et al 1977b) and food competition (Lau and Miczek 1977) situations. Results such as these tend to cast doubt upon the conclusions reached in earlier studies on the physiology of aggression, and they stress the necessity for at least a reformulation of ideas in the light of detailed behavioural analysis.

The most often used laboratory model of intraspecific fighting in rats has been shock-induced "aggression." Various authors have questioned the use at the term "aggression" in this context, suggesting that pain-elicited fighting more closely resembles defense (Scott 1966; Reynierse 1971; Powell 1974). In a recent thorough analysis of fhis issue, Blanchard's group has provided considerable support for these earlier suggestions (Blanchard, Blanchard, and Takahashi, 1977; Blanchard et a11977a; Blanchard, Blanchard, and Takahashi, 1978), They have demonstrated many parallels between the responses of shocked animals and those of colony intruders, and they have concluded that the behaviours displayed in response to shock are primarily defensive, not aggressive. In view of this detailed appraisal, it would seem imperative to revise many of the conclusions concerning the neural/neurochemical bases of "aggression" that have resulted from the use of this model. Of course, this suggestion would not necessitate a "scrap and start again" policy, but rather a reclassification in terms of mechanisms of defense. Examined in this manner, existing research findings on shock-induced defensive fighting might be correlated with results from future studies on the physiological analysis of intruder behaviour in a colony paradigm.

In his article, Adams makes an important distinction between patterns of defense and submission, but he seems rather uncertain concerning the classification of data from the shock-induced fighting literature. At one point he refers to defensive upright posture and boxing whilst in another context he considers that this posture is submissive, In view of the above discussion of Blanchard's studies, it would appear that the present formulation requires some revision in order to maintain internal consistency. This type of problem, I believe, reflects the fact that most researchers have not previously addressed themselves to specific questions concerning the physiology of agonistic behaviour. As a result, Adams, whilst achieving a remarkable synthesis of the data, has been forced (in many instances) to disentangle from the literature exactly which behaviours had been studied.

Adams has now provided us with preliminary, yet detailed, "models" of the neural circuitry involved in offensive, defensive, and submissive behaviour patterns. In the light of this invaluable service, and bearing in mind the foregoing discussion, surely the moment has come to argue for the precise evaluation of these "models" in relation to specific elements of agonistic behaviour?