Age and Other Factors in Motor Recovery from Precentral Lesions in Monkeys1

In man and in subhuman primates the paresis produced by lesions of the motor cortex is variable in respect of rate and of extent of ultimate recovery of motor power, Clinically various factors influencing recovery are recognized, such as the size and nature of the lesion and its location in the cerebral hemispheres, but the extent of recovery is generally unpredictable. In an experimental study these factors can be analyzed more precisely, and it is the purpose of this paper to present the results of such a study of the problem carried out on monkeys from which the various parts of the excitable motor regions of the cortex were extirpated. The regions removed were the motor and premotor areas, i.e., area 4 and area 6 a (upper part) of Vogt’s modification of Brodmann’s architectonic map of the cercopitheque brain (1, fig. l), Following extirpation observations were made on the rate and degree of ultimate recovery of motor power. The effects produced by such lesions were found to differ strikingly in the infant monkeys from those seen in adult animals.