Stereomotion processing in the non-human primate brain

The cortical areas that process disparity-defined motion-in-depth (i.e. cyclopean stereomotion) were characterised with functional magnetic resonance imaging in two awake, behaving macaques. The experimental protocol was similar to previous human neuroimaging studies. We contrasted the responses to dynamic random-dot patterns that continuously changed their binocular disparity over time with those to a control condition that shared the same properties, except that the temporal frames were shuffled. A whole-brain voxel-wise analysis revealed that in all four cortical hemispheres, three areas showed consistent sensitivity to cyclopean stereomotion. Two of them were localised respectively in the lower bank of the superior temporal sulcus (CSMSTS) and on the neighbouring infero-temporal gyrus (CSMITG). The third area was situated in the posterior parietal cortex (CSMPPC). Additional ROIs-based analyses within retinotopic areas defined in both animals indicated weaker but significant responses to cyclopean stereomotion within the MT cluster (most notably in areas MSTv and FST). Altogether, our results are in agreement with previous findings in both human and macaque and suggest that the cortical networks that process cyclopean stereomotion is relatively well preserved between the two primate species.