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

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EFFECTS OF CORTICAL AND STRIATAL LESIONS ON MOTOR PERFORMANCE IN MACAQUES* MURRAY H. BROWN The present study was undertaken to analyse further the inter- relations 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 main- tenance of the postural phases of motor activity. Localized disturb- ances 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 com- plex 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. Historical review The era of modern study of the striatal systems was inaugurated by Kinnier Wilson in 1913. Using macaques he approached the striate region via the insula with a Horsley-Clarke stereotaxometer and succeeded in stimu- lating and destroying portions of the putamen and pallidum. It was his belief that in the absence of a possible "steadying" effect of the lenticular nucleus on voluntary activity tremor was likely to develop, and that with increase of pyramidal excitation the tremor would increase. He believed, further, that the paleo- and neostriatum acted as a functional unit independent of the cortex; moreover, he found no evidence for a striatal center for auto- nomic movements. In 1924 Mella'5 reported induc

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