Microsaccades as a marker not a cause for attention-related modulation

Abstract

Recent evidence suggests that microsaccades are causally linked to the attention-related modulation of neurons - specifically, that microsaccades towards the attended location are required for the subsequent changes in firing rate. These findings have raised questions about whether attention-related modulation is due to different states of attention as traditionally assumed or might instead be a secondary effect of microsaccades. Here, in two rhesus macaques, we tested the relationship between microsaccades and attention-related modulation in the superior colliculus, a brain structure crucial for allocating attention. We found that attention-related modulation emerged even in the absence of microsaccades, was already present prior to microsaccades towards the cued stimulus, and persisted through the suppression of activity that accompanied all microsaccades. Nonetheless, consistent with previous findings, we also found significant attention-related modulation when microsaccades were directed towards, rather than away from, the cued location. Thus, in contrast to the prevailing hypothesis, microsaccades are not necessary for attention-related modulation, at least not in the superior colliculus. They do, however, provide an additional marker for the state of attention, especially at times when attention is shifting from one location to another.