Motivational Systems in Rats and Monkeys:
Are They Homologous
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The similarities between rat and monkey have been accentuated by both the experimental design and the analysis used in this paper. The subjects were restricted to adult males, animals with clearly defined differences in dominance, and socially isolated individuals. The tests were conducted only on pairs of animals, only for 10 min, and in a small, relatively empty test chamber. The analysis and writeup also were designed to enhance similarities in the results obtained from the two types of animals. Therefore, it is important to consider some of the differences that are not addressed by the present study.

The motivational system of defense, that may also be homologous in rats and monkeys, was not studied in the present experiment. It may be observed in wild muroid rodents [Adams, 1980] and in confrontations between dominant monkeys in the laboratory [Adams and Schoel, submitted for publication] .In the wild rat, the motor patterns of defense are similar to those of submission except that there is also a lunge-and-bite attack that is usually directed at the face of the opponent, a behavior that is not normally seen in laboratory rats. In the dominant monkey facing another dominant, as described in our more extended work, the motor patterns of defense included a frontal biting attack directed at the face or frontal part of the shoulders of the opponent. In the pairings of dominant monkeys defense also included a lunge accompanied by a characteristic facial expression called the open-mouth threat. In muroid rodents such as the rat there is apparently a neural mechanism that I have called the "consociate modulator" that switches the animal from defense to submission when the opponent is a familiar consociate animal, and the primary motivating stimuli determining the action of the consociate modulator are apparently olfactory [Adams, in press]. In primates, although there may also be a consociate modulator that activates a similar shift from defense to submission, it is apparently not based upon olfactory familiarity of the opponent, since defense occurs in pairs of familiar dominant monkeys. Instead, the motivating stimuli that determine the shift from defense to submission probably reflect the social history of the animal within the hierarchical structure of the monkey society.

Since the social history of the individual monkey within the structure of the society is critical for determining its behavior, one should be particularly careful about generalizations of primate behavior from a study, such as this one, that employs only dyadic relationships. Under more natural conditions, monkeys engage in more complex relationships involving three or more animals. For example, the dominance status of young animals is determined in part by the intervention of its mother on its behalf when it has become engaged in a fight with another individual, and as a result the dominance status of males may eventually reflect the dominance status of their mothers [Sade, 1967].

By using only socially isolated animals and confining them in a small, empty cage, the present study enhanced the rates of agonistic and sexual behaviors. Under normal conditions such as those encountered in field studies, agonistic and sexual behaviors are much less frequent. Instead, one may observe exploratory, feeding, burrowing or nestbuilding, playful, or parental behaviors that were not observed here.

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