Motivational Systems in Rats and Monkeys:
Are They Homologous
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Allogrooming occurred in both rat and monkey and in neither case was it associated with other categories of behavior. Although there was occasional allogrooming with the mouth by the monkey, similar to that of the rat, most of the monkey's allogrooming was done with the hands.

Submissive behaviors were remarkably similar in rat and monkey, as illustrated in Figure 3. Full submissive posture, crouching, running away, and squealing or screaming were all quite similar. In the rat there was also ultrasound vocalization, and in the monkey there were several facial expressions involving lip retraction, these behaviors having no equivalents in the other species.

In contrast to the above-listed categories of behavior, there was little resemblance in the motor patterns of patrol/marking in the rat and display in the monkey. In the rat, the motor patterns included olfactory-oriented sniffing of the cage (exploration) and the other animal, crawl-under, and crawl-over behaviors, including crawl-over-dish in which scent-marking was often deposited. In the monkey, display behaviors included repeated bouncing, climbing up and cage-shaking, patrol locomotion, and barking. The only similar motor act in the two species was patrol locomotion which was subsumed under exploration in the rat.

The time course of agonistic and sexual behaviors was markedly different for rats and monkeys. In the monkey most agonistic and sexual behavior took place in the first minute of testing and less and less occurred during the subsequent minutes of the test. In the rat, by contrast, both types of behavior did not usually begin until several minutes into the test session and they increased to a peak between 4 and 8 min into the session. In the monkey there was no obvious behavioral preliminary to attack or mounting, while in the rat there was prolonged olfactory investigation of the test chamber and of the intruder animal before attack (and resultant submission) or mounting occurred.

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