Motivational Systems in Rats and Monkeys:
Are They Homologous
Discussion Page 7

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The differences between the behaviors of rats and monkeys in the test situations employed here will be discussed in terms of the hypothetical organization of motivational systems. The theory of motivational systems has been derived from considerations of sequence analysis [Lehman and Adams, 1977] , brain mechanisms of offense, defense, and submission [Adams, 1979a] , and consideration of laboratory and ethological experiments on muroid rodents [Adams, in press]. Each motivational system, as described in detail in those publications, consists of four parts: a motivational mechanism, motor patterning mechanisms; sensory analyzers, and synthesizers for motivating stimuli; and sensory analyzers and synthesizers for releasing and directing stimuli.

The sensory analyzers and synthesizers of motivating stimuli have changed from predominantly olfactory analyzers in the rat to complex visual and auditory analyzers and synthesizers in the monkey. This is reflected in the completely different latencies before offense and sexual behavior in the rat and monkey. In the rat, it was only after a number of minutes of intensive olfactory investigation that offense or sexual behavior began. This reflects the importance for the rat, and other muroid rodents, of olfactory-motivating stimuli for offense and patrol/marking [Adams, in press] and probably sexual behavior as well. In the monkeys, by contrast, offense, sexual, and submissive behaviors began as soon as the animals caught sight of each other and before any olfactory investigation could take place. The motivating stimuli involved visual recognition of the opponent and probably involved a complex cortical synthesizing circuit for facial recognition that presumably is not developed in mammals like the rat.

The reliance of the monkey upon facial recognition rather than olfaction may have proved critical in the course of evolution for the development of the complex social structures that characterize primates and that are absent in muroid rodents. In rats and other muroid rodents, if a large group of animals is artificially created and a stranger is placed in their midst, the animals attack not only the stranger but also each other [Steiniger, 1950; Calhoun, 1956]. Apparently, the time course of olfactory recognition is too slow to allow for the fine differentiation required for maintenance of the coherent social groups found in primates.

The motivating stimuli of self-grooming may have remained constant from rat to monkey, consisting apparently of tactile stimuli associated with secretions from glands of the skin. However, the motivational significance of skin gland secretion may have changed. In the rat, secretion from the glands of the body apparently reflects patrol/marking and offense [Lehman and Adams, 1977]. In the monkey, on the other hand, self-grooming occurs following sexual and submissive behaviors as well as offense behaviors, suggesting that all three motivational systems activate motor patterns of skin gland secretion.

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