Abstract
While the middle temporal (MT) area has been extensively studied at the neural level to understand mechanisms of motion processing and selective attention, much less is known about the adjacent strip of parafoveal cortex, area MTC. In the macaque, area MT lies at the bottom of the superior temporal sulcus requiring deep electrode penetrations that traverse white and gray matter before reaching it. MT neurons are typically identified based on their receptive field (RF) size and direction selective responses. However, adjacent area MTC (also called V4t) has been reported to contain neurons with similar sized RFs, a significant portion of which have motion selective responses (Rosa & Elston, 1998). Here we examined the visual response properties and the modulation by pre-saccadic attention of area MTC, comparing it directly against MT in the same animal. We made recordings from linear arrays as a marmoset monkey performed a saccade foraging task selecting between peripheral random dot motion stimuli. Both area MT and MTC lie exposed at the cortical surface in the marmoset, making it possible to distinguish their border based on their retinotopy across successive recordings. We found that MTC had fewer neurons with direction selective responses consistent with previous reports (Rosa and Eltson 1998) and had more neurons selective for the orientation and spatial frequency of flashed gratings. We also measured how pre-saccadic attention modulates neural tuning curves for motion direction, comparing responses where a saccade was made towards the RF (i.e., attended) versus away from it. Neurons in both areas showed increases in baseline firing and in the gain of their tuning curves, but the increases in gain where larger in MTC while the increases in baseline were smaller. Despite a weaker net motion tuning in MTC, those neurons showed larger percentage increases in neural sensitivity for motion direction.