PARIETAL CORTEX AND MOVEMENT .1. MOVEMENT SELECTION AND REACHING

Recording studies in the parietal cortex have demonstrated single-unit activity in relation to sensory stimulation and during movement. We h ave performed three experiments to assess the effect of selective pari etal lesions on sensory motor transformations. Animals were trained on two reaching tasks: reaching in the light to visual targets and reach ing in the dark to targets defined by arm position. The third task ass essed non-standard, non-spatial stimulus response mapping; in the cond itional motor task animals were trained to either pull or turn a joyst ick on presentation of either a red or a blue square. We made two diff erent lesions in the parietal cortex in two groups of monkeys. Three a nimals received bilateral lesions of areas 5, 7b and MIP, which have d irect connections with the premotor and motor cortices. The three othe r animals subsequently received bilateral lesions in areas 7a, 7ab and LIP. Both groups were still able to select between movements arbitrar ily associated with nonspatial cues in the conditional motor task. Rem oval of areas 7a, 7ab and LIP caused marked inaccuracy in reaching in the light to visual targets but had no effect on reaching in the dark. Removal of areas 5, 7b and MIP caused misreaching in the dark but had little effect on reaching in the light. The results suggest that the two divisions of the parietal cortex organize limb movements in distin ct spatial coordinate systems. Area 7a/7ab/LIP is essential for spatia l coordination of visual motor transformations. Area 5/7b/MIP is essen tial for the spatial coordination of arm movements in relation to prop rioceptive and efference copy information. Neither part of the parieta l lobe appears to be important for the non-standard. non-spatial trans formations of response selection.