Does locomotion drive V1 activity in primates?

Our knowledge of the visual input to primary visual cortex (V1) has underpinned the last half century of visual neuroscience. The leaps taken in our ability to understand and interrogate the complex web of interconnected visual areas and their constituent circuits that make up the human visual pathway rest on this understanding of the earliest part of the visual cortex. Although the visual system is a convenient model system because it is relatively easy to present well-controlled inputs to subjects who sit still and keep their eyes steady, real vision occurs as part of a sensorimotor loop that has gone largely ignored within neurophysiological study. Our knowledge of how sensorimotor functions impact visual processing, even at the earliest stages of vision, is nascent and incomplete. These gaps in our understanding extend to even the behavior most core to our survival: our ability to locomote, to move through our environment. Efforts in model systems with visual pathways distinct from those of the primate have made promising insights into just how locomoting may affect the activity of the earliest areas of visual cortex, however, it remains unclear whether these findings generalize to the uniquely evolved primate visual system. In the body of this thesis, I describe and discuss the findings from an effort to discern whether locomotion-induced V1 modulations are present in a primate visual system, that of the common marmoset. I then discuss the challenges encountered in designing and performing these experiments in a recently-adopted model species and present the novel methods developed as a result. I primarily found that strong, population-level locomotion effects like those observed in rodents were not present in primate V1, however a subpopulation of cells does experience small modulations that correlate with locomotion. Additional analyses suggest an explanation based on differential magnitudes of gain fluctuations in mouse versus marmoset V1. The findings reported here indicate that there are fundamental differences in the pathways mediating behavioral input to mammalian V1 across species, presenting a case that cross-species generalizations about visual processing must be considered with greater care in the future.