A revised view of sensory cortical parcellation

TLDR

Traditional cortical parcellation schemes posit sharply defined, modality‑specific domains, but recent observations across species indicate that these domains are influenced by other senses, challenging the notion of strict modality exclusivity. The study aimed to systematically assess whether neurons in rat visual, auditory, and somatosensory cortex can be activated by stimuli from other senses. Using the rat cerebral cortex, the authors systematically recorded neuronal responses to cross‑modal stimuli across visual, auditory, and somatosensory areas. Within modality‑specific domains, multisensory neurons were rare, but at domain borders a cluster of multisensory neurons matched neighboring representations and integrated cross‑modal inputs to modulate responses, supporting a parcellation scheme where modality‑specific domains are separated by transitional multisensory zones.

Abstract

Traditional cortical parcellation schemes have emphasized the presence of sharply defined visual, auditory, and somatosensory domains populated exclusively by modality-specific neurons (i.e., neurons responsive to sensory stimuli from a single sensory modality). However, the modality-exclusivity of this scheme has recently been challenged. Observations in a variety of species suggest that each of these domains is subject to influences from other senses. Using the cerebral cortex of the rat as a model, the present study systematically examined the capability of individual neurons in visual, auditory, and somatosensory cortex to be activated by stimuli from other senses. Within the major modality-specific domains, the incidence of inappropriate (i.e., nonmatching) and/or multisensory neurons was very low. However, at the borders between each of these domains a concentration of multisensory neurons was found whose modality profile matched the representations in neighboring cortices and that were able to integrate their cross-modal inputs to give rise to enhanced and/or depressed responses. The results of these studies are consistent with some features of both the traditional and challenging views of cortical organization, and they suggest a parcellation scheme in which modality-specific cortical domains are separated from one another by transitional multisensory zones.