Abstract
Previous work in mice reported neuronal modulations in visual cortex by movements. Beyond the sizeable effects of locomotion, such modulations were associated with task-unrelated spontaneous body movements, challenging the view that the activity of neurons in early sensory cortices is driven predominantly by sensory input of a single modality. These modulations were not limited to stimulus-evoked responses but also observed for spontaneous activity, suggesting that the population activity in early sensory cortices spans multiple dimensions defined by ongoing behavioral states. To examine the possibility of modulation by body movements in non-human primates, we recorded extracellularly from neuronal populations in V1, V2 and V3/V3A (n=188, 92, 191 units, respectively) in three macaque monkeys, seated in primate chairs, while their body movements were monitored with multiple cameras. The animals maintained central fixation while visual stimuli (random dots, random lines, sinusoidal luminance gratings) or a blank screen were presented. One animal additionally performed a visual task that allowed us to manipulate spatial attention directed to the neuronal receptive fields. The definition of motion periods was based on the average of the absolute pixel-wise difference between successive video frames. For each unit, the modulation by movement was quantified with a movement index (MI): the difference in the stimulus-conditioned mean response in the presence and absence of body movements divided by their sum. MI averaged across units was modest, ranging -0.080 – 0.080 (mean = -0.004) across all areas and subjects but statistically significant for some areas (V1, V2 for one, V3/V3A for two animals, p<0.05, t-test). Conversely, the response modulation by attention measured with an index equivalent to MI was greater by an order of magnitude and increased monotonically from V1 to V3/V3A. These results, which contrast with those in mice, may reflect the varying degrees to which visual cortex specialized during evolution.