Effects of posterior parietal lesions on visually guided movements in monkeys

Four monkeys were trained to position, with either hand, a vertical rod in front of one of 5 target lights spaced 20 degrees apart on a semicircular screen. After the monkeys had reached the preoperative criterion (80% trials correct per session) they received a 1- or 2-stage bilateral lesion of posterior parietal cortex restricted to area 7. The lesion produced in all the monkeys considerable but temporary changes in movement latency, accuracy, velocity and duration. Latency increase appeared to be independent of changes in the other parameters. After the first lesion, movement latency increased for the contralateral arm in both left and right working spaces, from 100 ms up to 400 ms depending on the animal. A second lesion symmetrical to the first one increased movement latency of the arm contralateral or ipsilateral to the last lesion, depending on the time interval between the two lesions. In addition, unilateral lesions of area 7 induced a gross inaccuracy in movements of the arm contralateral to the lesion, more marked in the contralateral working space. These lesions also increased movement peak velocity and simultaneously decreased movement duration for the arm contralateral to the lesion. The increase in velocity appeared to be related to the decrease in duration. A second lesion of area 7 in the opposite hemisphere similarly affected accuracy, velocity and duration but for the arm contralateral to the second lesion.