Free behavior of rhesus monkeys following lesions of the dorsolateral and orbital prefrontal cortex in infancy.

Abstract

The present study sought to determine whether differential effects could be found in the free behavior of early-operated monkeys with selective removal of the dorsolateral and orbital prefrontal cortex. The early-operated monkeys were first observed in their home cages in stable living groups which had existed for at least 6 1/2 months (together condition) and then again immediately after they had been separated from one another (separated condition). The major results indicated that the monkeys with orbital lesions differed from unoperated controls in more ways than did the dorsolateral monkeys: in the together condition, the orbital group slept more and were more sedentary even when awake; in the separated condition, by contrast, they became hyperactive and spent most of their time in locomotion. These findings lend support to the notion, derived from studies of cognitive behavior in infant-operated monkeys, that functions of the orbital cortex, unlike those of the dorsolateral cortex, are not spared following brain damage in infancy. Further, the nature of the behavior exhibited by the impaired monkeys led to the suggestion that the orbital cortex may play an important role in modulating arousal mechanisms in the infant and adult monkey alike.