Cortical network hubs for perisaccadic visual processing: evidence from high resolution EEG and graph theory analysis

Abstract

Various spatial and temporal distortions occur around the time of a saccade (Morrone et al. Nature Neuroscience 2005), presumably associated with disruptions in cortical networks. However, these effects have not been investigated using network science approaches like graph theory analysis (GTA). Here, we constructed functional brain networks in a perisaccadic state, then evaluated which cortical regions play the role of hubs. Electroencephalography (EEG) was recorded via 64 channels in two behavioral conditions. Participants (N=9) were pre-cued with a series 1-3 grids (three horizontal lines, 10° by 10°) located 5° below the central fixation-point. In the saccade condition, saccades (recorded by Electrooculography) were cued by a sudden shift of the fixation-point to 10° left/right. 100ms later, a stimulus (three vertical lines; same size/location) was briefly presented (for 70ms). Saccades were occurred after the stimulus presentation. Fixation condition was identical, except the fixation-point remained in the centre. LORETA source localization was performed on the 200ms period following the saccade cue, or the equivalent time during fixation trials. Instantaneous coherences were calculated between all pairs of 84 Brodmann areas. GTA was implemented to find eigenvector centrality (EC) of all areas. Nonparametric permutation test showed significant enhancement of EC (gamma-band) for the saccade task (relative to the fixation task) in right inferior parietal cortex (Brodmann areas 39, 40, 41), left inferior parietal cortex (areas 39, 40) and right frontal cortex (area 8). These results suggest that inferior parietal regions, especially bilateral supramarginal gyrus (SMG), and right frontal eye field (FEF) are involved in information processing for perisaccadic visual processing and participate as hubs in the functional perisaccadic network. These results are consistent with studies that suggest the role of FEF and SMG as important regions in saccadic memory and integration (Prime et al. Cerebral Cortex 2009; Dunkley et al., Cortex, 2016).