Neural subpopulations in marmoset area MTC but not MT show extra-retinal tuning for saccade direction

Previously we found pre-saccadic neural enhancements in two adjacent motion processing areas of the marmoset monkey, middle temporal (MT) and middle temporal crescent (MTC) areas (Bucklaew et al., VSS, 2021). While area MT has been the focus of previous studies much less is known about area MTC, which in macaque corresponds to areas V4t and MST lateral. Area MTC contains a high proportion of neurons selective to stimulus motion and with receptive fields slightly larger than MT (Elston & Rosa, 1999). In the marmoset it is straight-forward to distinguish between these areas based on their retinotopy across successive electrode penetrations. Here we asked if the two areas differ based on how they integrate extra-retinal feedback during saccades. We recorded from neurons in both areas as two monkeys freely viewed either natural images or a blank screen. For natural images we observe that MT neurons show classic patterns of saccadic suppression around saccade onset followed by a post-saccadic increase 50% over baseline after 50ms. By contrast, for blank backgrounds MT neurons show less than 10% modulation for either suppression or post-saccadic increases. Area MTC differed from MT in that the early response interval (<50ms) showed a distinct peak rather than suppression. There was on average a 54% early increase with natural images, and that increase remained significant for blank backgrounds. This early peak in response likely reflects an extra-retinal feedback to MTC. We found that the early peak was driven by a subpopulation of cells (24%) that had strong modulations (50% or greater) and that showed significant tuning for the direction of saccade. This suggests that area MTC differs from MT in that it receives extra-retinal feedback about the direction of saccades.