Corticocortical connections of visual, sensorimotor, and multimodal processing areas in the parietal lobe of the...

We studied the corticocortical connections of architectonically defined areas of parietal and temporoparietal cortex, with emphasis on areas in the intraparietal sulcus (IPS) that are implicated in visual and somatosensory integration. Retrograde tracers were injected into selected areas of the IPS, superior temporal sulcus, and parietal lobule. The distribution of labeled cells was charted in relation to architectonically defined borders throughout the hemisphere and displayed on computer-generated three-dimensional reconstructions and on cortical flat maps. Injections centered in the ventral intraparietal area (VIP) revealed a complex pattern of inputs from numerous visual, somatosensory, motor, and polysensory areas, and from presumed vestibular- and auditory-related areas. Sensorimotor projections were predominantly from the upper body representations of at least six somatotopically organized areas. In contrast, injections centered in the neighboring ventral lateral intraparietal area (LIPv) revealed inputs mainly from extrastriate visual areas, consistent with previous studies. The pattern of inputs to LIPv largely overlapped those to zone MSTdp, a newly described subdivision of the medial superior temporal area. These results, in conjunction with those from injections into other parietal areas (7a, 7b, and anterior intraparietal area), support the fine-grained architectonic partitioning of cortical areas described in the preceding study. They also support and extend previous evidence for multiple distributed networks that are implicated in multimodal integration, especially with regard to area VIP.