Abstract
To interact effectively with our environment, we need to specify the intended outcomes (goals) of our actions. In this process, immediate goals and final goals can be regarded as different levels within a hierarchically organized system for action planning: immediate goals and movement details are selected to accomplish more remote goals. Behavioral studies support this notion of different levels of action planning, but the neurophysiological basis remains unclear.
Using fMRI, we examined the neural correlates of preparing object manipulations based on either the desired end-state (the final goal) or the initial movement towards a target (the immediate goal). Subjects had to insert an object (consisting of a large and a small cube) into one of two corresponding large and small slots. The subjects were cued on either which slot to fill (Final Goal trials) or which object part to grasp (Immediate Goal trials). These actions required similar movements, but different planning.
During Final Goal trials, there was differential preparatory activity along the superior frontal gyrus (bilaterally) and in left inferior parietal cortex. Immediate Goal trials evoked differential activity in occipito-parietal and occipito-temporal cortex. These findings support the notion that actions can be planned at different levels. We show that different fronto-parietal circuits plan the same action, by a relative emphasis on either selecting a sequence of movements to achieve a desired end-state, or selecting movements spatially compatible with given object properties.
