Order-Dependent Functional Brain Connectivity in a Cue-Separation Grasp Task

Prehension involves location-dependent reach transport and orientation-dependent grasp components. To understand how the brain integrates object location and orientation for grasp, we studied how the order of transport / grasp cues influences whole brain functional connectivity. We collected BOLD signal data from 12 participants in an Event-related fMRI Experiment. Participants were instructed to reach and grasp a cube illuminated to the left or right of midline (Location Cue: L) and a verbal instruction to orient the hand for vertical or horizontal grasp (Orientation Cue: O). The order of these cues (LO vs. OL) varied randomly. fMRI data were analyzed separately based on three predictors: Delay 1 (between the two cues), Delay 2 (between the 2nd cue and go signal), and an Action Phase. Graph Theory Analysis was performed based on 200 regions of interest (nodes) at each phase. Preliminary analysis based on 3 participants: During Delay 1, nodes coalesced into three modules: 1) a central parietofrontal strip approximating primary somatomotor cortex, 2) two more anterior-posterior premotor / visuomotor parietofrontal regions, and 3) a ring of cortex skirting 1+2 but with no occipital/temporal involvement. Occipital involvement increased in Delay 2. Parietofrontal Modules 1 + 2 joined (reducing to two modules) after Delay 2 for LO and the action phase for OL, i.e., always after the location cue. The Global Clustering Coefficient is always reduced in the action phase. We conclude the order of L-O cues influences modularity, such that location information produces more parietofrontal ‘binding’, presumably in preparation for transport.