Abstract
Behavioral studies show that motor actions are planned by adapting motor programs to produce desired visual consequences. Does this mean that the brain plans these visual consequences independent of the motor actions required to obtain them? Here we addressed this question by investigating planning-related fMRI activity in human posterior parietal (PPC) and dorsal premotor (PMd) cortex. By manipulating visual movement of a virtual end-effector controlled via button presses we could dissociate motor actions from their sensory outcome. A clear representation of the visual consequences was visible in both PPC and PMd activity during early planning stages. Our findings suggest that in both PPC and PMd action plans are initially represented on the basis of the desired sensory outcomes while later activity shifts towards representing motor programs.
Highlights
Reaches are realized through complex movements of individual joints, even though the resulting hand trajectories look surprisingly straight and have simple velocity profiles [1]
Reaction times in pre-planned movement task” (PPM) trials were contrasted to those revealed in direct movement task” (DM) trials, as in the latter trials planning could take place only in the movement epoch allowing us to estimate the reaction time benefit through pre-planning (Rosenbaum 1980)
If we assume a processing hierarchy between these areas, our findings suggest that posterior parietal cortex (PPC) delineates a rather general and abstract action plan in visual terms, which is subsequently translated into more specific motor programs by PMd [32], [57], [58]
Summary
Reaches are realized through complex movements of individual joints, even though the resulting hand trajectories look surprisingly straight and have simple velocity profiles [1]. This suggested that the central nervous system aims at producing desired visual actions and adapts motor plans . Wolpert and colleagues [2] confirmed that notion by an experiment, in which a mismatch between the actual hand position and the visual feedback thereof was manipulated. Despite this mismatch, subjects reached along visually straight trajectories.
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