Abstract

How is spatial information for limb movement encoded in the brain? Computational and psychophysical studies suggest that beginning hand position, via-points, and target are specified relative to the body to afford a comparison between the sensory (e. g., kinesthetic) reaf-ferences and the commands that generate limb movement Here we propose that the superior parietal lobule (Brodmann area 5) might represent a substrata for a body-centered positional code. Monkeys made arm movements in different parts of 3D space in a reaction-time task. We found that the activity of area 5 neurons can be related to either the starting point or the final point or combinations of the two. Neural activity is monotonicalty tuned in a body-centered frame of reference, whose coordinates define the azimuth, elevation, and distance of the hand. Each spatial coordinate tends to be encoded in a different sub-population of neurons. This parcellation could be a neural correlate of the psychophysical observation that these spatial parameters are processed in parallel and largely independent of each other in man.

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