FMRI Study on the Neural Mechanisms of Sensorimotor Transformations

We used a blocked fMRI design to investigate the neural mechanisms of action planning in internal versus external space. The subject's arm was positioned alongside the body with the forearm semi-pronated. Vertical position of a cursor on the screen was controlled by ringer flexion/extension measured with an MRI-compatible data glove. For each trial, subjects moved a cursor within from a centrally-positioned start to an upper or lower target. An MRI-compatible torque motor randomly rotated the forearm into pro/supination. In separate blocks, forearm rotation occurred before or after the target appeared, forcing a motor plan update based on target position or on forearm orientation, respectively. In control blocks, the target and forearm orientation remained consistent, so as not to require trial-to-trial re-planning. Re-planning in internal space was associated with activation in the left ventral premotor cortex and bilateral inferior parietal lobule. Re-planning in external space was associated with activation in the superior parietal lobule. These data build on the role of premotor and parietal cortices in sensorimotor transformations.