Abstract
The processing of visual motion is conducted by dedicated pathways in the primate brain. These pathways originate with populations of direction-selective neurons in the primary visual cortex, which projects to dorsal structures like the middle temporal (MT) and medial superior temporal (MST) areas. Anatomical and imaging studies have suggested that area V3A might also be specialized for motion processing, but there have been very few studies of single-neuron direction selectivity in this area. We have therefore performed electrophysiological recordings from V3A neurons in two macaque monkeys (one male and one female) and measured responses to a large battery of motion stimuli that includes translation motion, as well as more complex optic flow patterns. For comparison, we simultaneously recorded the responses of MT neurons to the same stimuli. Surprisingly, we find that overall levels of direction selectivity are similar in V3A and MT and moreover that the population of V3A neurons exhibits somewhat greater selectivity for optic flow patterns. These results suggest that V3A should be considered as part of the motion processing machinery of the visual cortex, in both human and non-human primates.
Highlights
The primate visual system consists of numerous brain regions that represent stimuli in contralateral visual space
There is some evidence that neural activity in V3A is concerned with visual motion (Galletti et al, 1990; Tootell et al, 1997; Vanduffel et al, 2002; Anderson and Martin, 2005; Chen et al, 2016), very little is known about the selectivity of single neurons in this area
As described in Materials and Methods, we identified area V3A on the basis of MRIs taken before the recordings and a CT scan performed with the recording electrode in place
Summary
Area V3A is frequently the target of anatomy and imaging studies, little is known about its functional role in processing visual stimuli. We report a detailed study of direction selectivity in V3A. Our results show that single V3A neurons are, on average, as capable of representing motion direction as are neurons in wellknown structures like the middle temporal area (MT). We identify a possible specialization for V3A neurons in representing complex optic flow, which has previously been thought to emerge in higher-order brain regions. It appears that V3A is well suited to a functional role in motion processing
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