Attention modulates V4 neural activity across and in the absence of microsaccades

Recent work revealed that attention-related modulation of cortical and subcortical neuronal activity can depend on the presence and direction of microsaccades. In cortical area V4, attentional modulation is reported to occur only after a microsaccade is made towards an attended location (Lowet, et. al., 2018). On the other hand, attentional modulation in the subcortical superior colliculus (SC) occurs in the absence of microsaccades and when a microsaccade is made toward an attended target (but not away from a target; Yu et. al., 2022). This discrepancy may arise because of differences between SC and V4, task differences and/or task difficulty. We investigated population measures of attention in V4 around the time of microsaccades while monkeys performed a visual-spatial attention task. Monkeys detected an orientation-change in one of two simultaneously presented oriented Gabors. Monkeys fixated and reported an orientation change by saccading to the changed stimulus. Attention was cued to a stimulus location using a visual cue on instruction trials at the start of each block of trials. Cue validity varied across blocks with some blocks cued with an 80/20% cued/uncued regime, similar to work in SC, while others used a 50/50% regime. We recorded over 3500 V4 single- and multi-units from implanted Utah arrays. We compared the average population response aligned to microsaccade onset when monkeys attended a target within neural receptive fields versus when they attended a target outside of neural receptive fields. Contrary to previous reports in V4, we found that attention modulated V4 activity prior to and after microsaccades, regardless of microsaccade direction. We found this even when we shuffled across or averaged over microsaccade direction, indicating that attentional modulation of V4 is independent of microsaccades in this task. Our results suggest that certain task parameters may be key in determining how microsaccades interact with attention.