Distinct representations of planned reach trajectories in human premotor and posterior parietal cortex

ABSTRACT Goal-directed movements of the hand are often directed straight at the target, e.g. when swatting a fly; but when drawing or avoiding obstacles, hand trajectories can also become quite complex. Studies on movement planning have largely neglected the latter case and the question of whether the same neural machinery is planning straight, saccade-like vs. complex hand trajectories. Using time-resolved fMRI during delayed response tasks we examined planning activity in human superior parietal lobule (SPL) and dorsal premotor cortex (PMd). We show that the recruitment of both areas in trajectory planning differs significantly: PMd represented both straight and complex hand trajectories while SPL only those that led straight to the target. This implies that complex and computationally demanding reach planning is governed by a frontal pathway while a parietal route could warrant an alternative and faster way to put simple plans into action.