Beyond Reach I: Neuroimaging Reveals Different Cortico-cerebellar Networks for Grasp vs. Object Placement.

Object manipulation usually involves both acquisition and placement, but neuroimaging studies tend to focus on its initial reach-to-grasp component. To understand how grasp and placement are represented in the brain, we designed an event-related fMRI study in which 20 participants alternated between grasping / placing a rectangular object from / toward templates presented at variable locations and orientations on an inclined plane. Despite the similarity in target information (i.e., location and orientation), we expected to see sensory and intentional task differences, as the grasp relied on matching the hand to the object, whereas placement relied on matching the object to the template. For our analysis, we examined BOLD activation across two epochs (planning phase before movement onset and execution phase during the movement), and applied graph-theoretical analysis (GTA) of whole-brain functional connectivity based on the joint time series from these two epochs. In both tasks, we found that common activation was more focused on prefrontal regions during planning and on sensorimotor regions during execution, with a specific increase in cerebellar activation during placement. Furthermore, the greater placement activation was also found in action-related regions of interest during the planning phase, and they could accurately decode between our two tasks. GTA categorized the two networks into three identical modules (prefrontal, cerebellar-occipito-parietal, and sensorimotor) and found task-based differences in modularity scores in the prefrontal and cerebellar-occipito-parietal modules. Overall, these data show that although reach-to-grasp and reach-to-place movements share extensive neural circuitry, they also exhibit task-specific differences, likely related to differences in intentionality during planning and in sensory feedback during movement execution.