Functional connectivity for updating grasp plans across saccades: An fMRIa study.

Abstract

The cortical mechanisms associated with grasping and spatial updating have been investigated separately, but no study has investigated the functional connectivity associated updating grasp plans across saccades. Here, we identified potential network nodes using an fMRI adaptation task, and then performed a functional connectivity analysis. Based on a previous perceptual experiment (Dunkley et al., 2016), we hypothesized that supramarginal gyrus (SMG) would be a central hub for updating grasp orientation signals across saccades. Participants (n=17) fixated looked to the left or right of a central oblong object that was briefly presented at one of two orientations. During grasp preparation, participants either maintained fixation (‘Fixation’ condition) or moved gaze to the other LED (‘Saccade’). The object was then re-presented at either the same (‘Repeat’) or other (‘Novel’) orientation. Lastly, participants grasped the object and returned to rest. Analysis of the Novel/Repeat and Saccade/Fixation conditions revealed a cluster of parietal regions specifically sensitive to object changes that occurred across saccades, including intraparietal cortex, superior parietal cortex, and right SMG. To further test our hypothesis, we used a separate localizer to identify peak saccade activity in left and right SMG which we used as seed regions for a psychophysiological (PPI) analysis during the Saccade / grasp preparatory period of the main task. Right SMG activity was significantly correlated with activity in the right frontal eye field (FEF), left supplementary eye field (SEF) and right superior parietal lobe (SPL), extending into posterior-anterior intraparietal sulcus (p-aIPS). Left SMG activity was significantly correlated with activity in right FEF, left SEF, primary motor cortex, left SPL, p-aIPS (trending), and the medial occipitotemporal sulcus. These results confirm that, when saccades occur during grasp preparation, SMG activity integrates object orientation across saccades and is functionally correlated with a network of cortical areas that includes both saccade and grasp areas.

Acknowledgement: 1: NSERC Brain-in-Action CREATE Program, 2: NSERC Discovery Grant, 3: Canada Research Chair Program, 4: OGS/QEII-GSST