Cortical Integration of Multimodal Cues for Reach / Grasp planning

Abstract

Daily tasks, such as picking up a cup, require the integration of two successive movements: an initial reach toward the target and a final grip around the cup. While the cortical mechanisms for reach and grasp were explored extensively, the mechanisms that integrate these components are not yet established. Here, we used functional magnetic resonance imaging to investigate which brain areas are involved in integrating information about object location and grasp orientation into the movement plan using a cue-separation paradigm. Participants grasped vertically or horizontally a cubic object presented to the left or the right of their body midline. Two successive cues preceded the grasping movement onset: a visual cue of the target location (L) and an auditory cue of the target orientation (O). In the O-L condition, the orientation cue was followed by the location cue; in the L-O condition, the location cue was followed by the orientation cue. A delay period followed each cue presentation. Whereas the first delay only required participants to remember one cue, the second delay required participants to remember two cues and integrate them as they prepared to initiate the reach-and-grasp movement. We conducted the conjunction analysis to assess which areas showed a greater response during the second than the first delay regardless of the order the sensory information was presented. We expected to see an increase in activity in motor-related areas as participants integrate the cues and prepare for action. We found increased activities in the left Supplementary Motor Area (SMA) and the bilateral Early Visual Cortex (EVC). Suggesting that not only are motor-related regions like SMA involved in action preparation, but the EVC also partakes in the final motor planning. This could indicate a top-down processing where higher-order motor regions interact with lower-order visual areas to gather information relevant for action preparation.