The posterior parietal cortex and non-spatial cognition

Abstract

The primate posterior parietal cortex (PPC) processes information related to environmental physical space. The human PPC has apparently expanded not only in size but also in its functional range to encompass certain abstract and higher-order conceptual spaces. In this report, we review various forms of non-spatial representation in the PPC. These forms are presented roughly in order of the level of abstraction of the 'objects' and pseudo-spatial relations represented. Also, we consider mechanisms that could have enabled the hominid PPC to establish such representations. Lastly, we offer a general principle to unify the newer forms of representation with the original functions of the PPC.

Figure 1.. Comparison of substructures (unshaded) of monkey and human posterior parietal cortex (PPC)

(a) monkey PPC; (b) human left PPC; (c) human right PPC. Results of meta-analysis (based on the references listed in Figure 2) of cortical areas responsible for non-spatial cognition are superimposed. Data points in monkeys are projected onto the left hemisphere (because no particular laterality has been claimed), whereas those in human subjects are illustrated independently for each hemisphere (being biased toward the left hemisphere). Large and dashed symbols indicate areas estimated from reviews and original papers, respectively, in which coordinates were not clearly specified. Arabic numerals indicate Brodmann areas (40: supramarginal gyrus; 39: angular gyrus). The subdivisions of the PPC were referred from the original sources. AIP, anterior intraparietal area; CIP, caudal intraparietal area; CS, central sulcus; IPS, intraparietal sulcus; LIP, lateral intraparietal area; MIP, medial intraparietal area; PCS, post central sulcus; POS, parieto-occipital sulcus; SF, sylvian fissure; STS, superior temporal sulcus; VIP, ventral intraparietal area.

Figure 2.. Hypothetical mechanisms of non-spatial representations processed by posterior parietal cortex as a function of abstractness

Left, hypothesized mechanism for increasing abstract levels of representations (see ‘Future directions’ section for details). Right, structure of various levels of abstract spaces (references for respective levels are listed in the far-right column). 3D, three-dimensional; 4D, four-dimensional; AG, angular gyrus; AIP, anterior intraparietal area; CIP, caudal intraparietal area; IPL, inferior parietal lobule; IPS, intraparietal sulcus; LIP, lateral intraparietal area; PPC, posterior parietal cortex; SII, secondary somatosensory cortex; SMG, supramarginal gyrus; SPL, superior parietal lobule; TPJ, temporo-parietal junction.