Brain Mechanisms

Limits of neurophysiological approaches to aggression. As a student of aggressive behavior but a nonspecialist in the research area addressed by David Adams, I am pleased to comment on his provocative and scholarly article in the general terms appropriate to an interested outsider.

What I find mildly disturbing is that the doctrine of neural centers appears to have been resurrected as an unspoken theme throughout Adams's article. For example, we are told that "The sensory filters for the motivating stimuli of offense tuned to unfamiliar conspecific odors are apparently located in the amygdala. ..." This suggests that there is a one-to-one correspondence of behavior (or function) and anatomical locus, a point of view which I understood to be outdated, partly because logically there is a "proving the null hypothesis" quality about it. If neurons of structure A are active during a particular behavior X, this by no means proves that structure A is the locus of behavior X, since cells of structures B, C, F. and Z may also be active but unrecorded by the investigator. If structure A is stimulated electrically or chemically, behavior X may occur, but similar logical problems prohibit us from concluding that A is the seat of X. If removal of A is followed by cessation of behavior X, there are the worst kinds of logical problems, reminiscent of the case of a psychologist who removed all the legs from a cockroach trained to jump on a verbal command. The conclusion (when the now legless cockroach fails to jump) that cockroaches have their auditory apparatus in their legs is similar to the type of conclusion frequently drawn in physiological psychology from lesion/ablation studies. Because the body of literature so ably integrated by Adams is based largely on recording, stimulation, and lesioning studies, a great deal of caution is called for in making statements about behavioral loci or centers.

As an ex-engineer, I have always felt that the term "hard-wired" was a misnomer when applied to behavior. For example, Milgram, Devor, and Server (1971) found that there were spontaneous changes in the behaviors (feeding and drinking) elicited by lateral hypothalamic stimulation. Others have reported similar findings (Mogenson 1971; Valenstein, Cox, and Kakolewski 1969). Such plasticity is not what one expects in a "hard-wired" system. If phenomena such as this appear when the behavioral variables are relatively easy to measure (amount eaten or drunk), how much more "plastic" things are likely to be when the behavioral categories are offense, defense, and submission.

It is easy to point out difficulties and ambiguities in interpretation, and to be a curmudgeon. My main point is that the underlying assumption (or article of faith) of Adams's paper is that we can ultimately point to places in the nervous system that map onto behavior point for point. Adams ends with the speculation that the "master switch" may reside in the older parts of the cerebellum. While the shifts between offense, defense, and submission undoubtedly have neural correlates, and hormonal ones as well, to look for a single place where this happens seems to me to be misguided.