Differential parietal activations for spatial remapping and saccadic control in a visual memory task

Remapping is a process that updates visual information in internal spatial representations across eye movements, allowing for stable perception of the environment. Previous work has demonstrated visual remapping activity in parietal cortex during saccades, but it remains unclear whether remapping is triggered by overt saccades only (or by attentional shifts also), and whether it engages parietal areas only (or other cortical areas). Here, we used fMRI to investigate spatial remapping during two visuospatial memory tasks requiring either overt (accompanied by a saccade) or covert (with central fixation) attention shifts to peripheral distracters. Participants had to remember the position and color of a lateralized dot during a saccade or attention shift, requiring them to update the dot position in memory, and then indicate if a second dot matched the first. Differential activation patterns were observed within parietal cortex as a function of the different visual, motor, and interhemispheric remapping demands in the saccade task, presumably mediating the maintenance of spatial position in perceptual and motor maps. Remapping engaged parietal areas adjacent to, but not overlapping with, those activated by saccade execution, while it did not engage the frontal eye fields, pointing to distinct neural substrates for ocular motor and spatial updating processes. No differential activation related to remapping was found during the covert attention shift task, suggesting that this condition did not necessitate the same remapping as the saccade condition. Overall these results further elucidate the mechanisms of spatial remapping in human parietal cortex and their relationship with attention processing and ocular motor behavior, with implications for understanding visuospatial attention deficits in hemispatial neglect.