Visual topography of human intraparietal sulcus

Human parietal cortex is implicated in a wide variety of sensory and cognitive functions, yet its precise organization remains unclear. Visual field maps provide a potential structural basis for descriptions of functional organization. Here, we detail the topography of a series of five maps of the contralateral visual hemifield within human posterior parietal cortex. These maps are located along the medial bank of the intraparietal sulcus (IPS) and are revealed by direct visual stimulation during functional magnetic resonance imaging, allowing these parietal regions to be routinely and reliably identified simultaneously with occipital visual areas. Two of these maps (IPS3 and IPS4) are novel, whereas two others (IPS1 and IPS2) have previously been revealed only by higher-order cognitive tasks. Area V7, a previously identified visual map, is observed to lie within posterior IPS and to share a foveal representation with IPS1. These parietal maps are reliably observed across scan sessions; however, their precise topography varies between individuals. The multimodal organization of posterior IPS mirrors this variability in visual topography, with complementary tactile activations found immediately adjacent to the visual maps both medially and laterally. These visual maps may provide a practical framework in which to characterize the functional organization of human IPS.