Perisaccadic V1 activity is not due to shifting visuo-spatial attention

It has been previously shown in human imaging studies that striate cortex is active when saccadic eye movements are executed even in the absence of visual input. It is commonly accepted that a shift in visuo-spatial attention immediately precedes saccades. Therefore, it is plausible that perisaccadic V1 responses could be the product of this shift in visuospatial attention rather than being directly related to saccadic activity. We have studied functional MRI in 13 subjects who either executed saccades reflexively to visual targets or performed voluntary saccades in the absence of visual stimuli. Eye movements were recorded with an MR compatible eye tracker. Perisaccadic cortical responses were compared to responses obtained when attention was covertly directed to the same peripheral locations while maintaining central fixation. Results show, besides frontal and parietal activation foci, strong perisaccadic V1 activity whether a visual target is present or not. Shifts of attention are associated with activation in parietal and frontal cortices but not in V1. These findings suggest a dynamic interplay between visual and oculomotor cortex while subjects perform saccades.