MESOSCALE ORGANIZATION OF MOTION-SENSITIVE AREAS OF THE DOSAL VISUAL STREAM

Despite half a century since the discovery of direction-selective neurons in the primate extrastriate cortex (Zeki, 1974), and evidence of their columnar organization within area MT (Salzman et al., 1990), the precise mesoscale organization, both parallel and perpendicular to the cortical surface, of neurons selective for motion direction, axis-of-motion, and optic flow patterns remains poorly understood, especially in areas beyond MT. Here, we leveraged the high sensitivity, exquisite resolution (0.002 mm³ at ~2 Hz), and large spatial coverage (~1 cm³) of three-dimensional functional ultrasound imaging (3D-fUS) to investigate the mesoscale organization of motion selectivity across regions of the dorsal visual and parietal cortex. Using this approach, we mapped regions along posterior portions of the superior temporal sulcus (STS) and the inferior parietal sulcus (IPS) while rhesus monkeys (n = 3) passively fixated on visual stimuli comprising optic flow patterns (rotation, expansion, contraction, and translation) and moving stimuli (dots, lines, and textures) varying in axis and direction of motion. Our results reveal a highly reproducible mesoscale functional organization for axis-of-motion, direction-of-motion, and optic flow selectivity. In addition to MT, we observed structured motion representations in occipital areas: V4d, V3A, and MST, and parietal regions: 7a, LIPv, LIPd, LOP, and PEc/ci. Alongside clear direction-preference columns in MT, we find evidence for laminar differences in motion selectivity in higher-order areas such as LIPd/LIPv. We demonstrate that 3D-fUSI enables comprehensive mapping of motion-selective functional architecture across multiple cortical areas, providing new insights into the mesoscale organization of visual motion processing in the primate brain.