Visual Topography of Human Intraparietal Sulcus

Abstract

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.

Functional Heterogeneity in Posterior Parietal Cortex Across Attention and Episodic Memory Retrieval

“…Just as recent studies in visual (Brewer et al 2005;Larsson and Heeger 2006;Sayres and Grill-Spector 2008;Arcaro et al 2009;Kolster et al 2010;Grill-Spector 2010, 2011;Rauschecker et al 2011), frontal (Hagler and Sereno 2006;Kastner et al 2007), and parietal cortex (Levy et al 2007;Swisher et al 2007) illustrate the benefit of multiple experimental techniques for clarifying the complexity of neural organization in both topographic and nontopographic areas, the present study demonstrates the generalizability of this approach to regions involved in multiple aspects of memory and attention. In particular, our results reveal heterogeneity across topographically organized PPC subregions, with 1) IPS0 displaying a distinct pattern of activity from IPS4, IPS5, and SPL1, and 2) IPS1-3 not exhibiting differential responses across retrieval conditions (though future studies with additional power are required to draw definitive conclusions about the relative effects of retrieval outcomes on responses in these areas).…”

“…The boundaries of visual field representations in posterior parietal areas IPS0-5 and SPL1 were defined using established phase-encoded retinotopic mapping methods (Engel et al 1994;Tootell et al 1998;Silver et al 2005;Swisher et al 2007;Konen and Kastner 2008a;Bressler and Silver 2010;Szczepanski et al 2010). Maps were defined with a coherence threshold of 0.15 for each subject, a value that is consistent with prior work (e.g., Brewer et al 2005).…”

“…5). Surface-rendered phase maps were examined by 2 experienced raters (KSW and DWB) who defined the locations and boundaries of the parietal maps based on guidelines in the published literature (Silver et al 2005;Swisher et al 2007;Konen and Kastner 2008a;Szczepanski et al 2010). Critically, the areal boundaries were defined blind with respect to the retrieval data obtained from the 5 participants in the attention mapping experiment.…”

“…This procedure defined, within each hemisphere of each subject, maps along the IPS0-IPS5 and in the SPL1 associated with the allocation of top-down spatial attention (Tootell et al 1998;Sereno et al 2001;Silver et al 2005;Swisher et al 2007;Konen and Kastner 2008a;Silver and Kastner 2009). The attention maps were then compared with the retrieval effects observed in these participants (see Methods and Results sections), allowing us to directly evaluate which, if any, regions containing topographic attention maps are recruited during episodic retrieval.…”

The neural representation of sensorimotor transformations in a human perceptual decision making network

“…From studies that examine the human IPS, it is apparent that the human region is also well positioned to play a key role in sensorimotor transformations. Functional connectivity analyses have shown a tight correlation between visual cortex and IPS activity during visuospatial processing (Kayser et al, 2010a;Sereno et al, 2001;Silver et al, 2005;Swisher et al, 2007), and manipulation of visuospatial or featurebased attention modulates IPS activity (Corbetta and Shulman, 2002;Kayser et al, 2010b, respectively). Further studies have also correlated IPS activity with evidence accumulation (Kayser et al, 2010a;Ploran et al, 2007) and motor intention (Hesse et al, 2006;Rushworth et al, 2003); and a number of studies investigating visuomotor control show activation within and around IPS (reviewed in Culham et al, 2006).…”