The Effects of Cortical and Striatal Lesions on Motor Performance in Macaques *

The present study was undertaken to analyse further the interrelations between different parts of the extrapyramidal motor system. This cortico-strio-nigral hierarchy has, since the work of Kinnier Wilson,28 been recognized as concerned primarily with the maintenance of the postural phases of motor activity. Localized disturbances in the system are held responsible for certain resting "tremors" and "rigidities" of man; the results so far obtained from experiments based on this hypothesis have, however, proved disappointing, largely because of anatomical difficulty in separating the pyramidal from the extrapyramidal systems. By means of the Horsley-Clarke stereotaxic instrument, it is possible to place discrete lesions in various parts of the striatal complex without injury to pyramidal tracts. Since discrete ablations of extrapyramidal regions are easily made, destruction of portions of this system may be variously combined and the physiological effects compared. The term "extrapyramidal" is employed here to include all descending motor pathways and their cells of origin, with the exception of the cortico-spinal and cortico-nuclear tracts contained in the pyramidal system.