The supramarginal gyrus straddles the boundary between somatosensory association cortex and the language network, reflecting the structural fact that the lateral fissure separates parietal cortex above from temporal cortex below, and that the inferior parietal lobule wraps around its posterior end. The territory is a phylogenetic latecomer: the supramarginal and angular gyri together form Geschwind’s “association cortex of association cortex,” with connectivity to most of the other high-level systems in the brain.

Cytoarchitectonic parcellations of the inferior parietal lobule by the Düsseldorf group (Caspers et al. 2008) divide it into seven sub-areas, five of which lie in the supramarginal gyrus alone. The functional specialisations of these subdivisions are still being worked out, but finer-grained imaging suggests phonological processing localises to the more anterior supramarginal cortex while semantic and number-related processing extends caudally into the angular gyrus.

Right-hemisphere supramarginal lesions are a classic substrate for hemispatial neglect, in which patients fail to attend to the contralateral side of space despite intact primary sensory and motor function. Neglect is more often associated with right-hemisphere damage than left, an asymmetry that mirrors the language asymmetry.