Abstract
Sounds activate occipital regions in early blind individuals. How different sound categories map onto specific regions of the occipital cortex remains however debated. We used fMRI to characterize brain responses of early blind and sighted individuals to familiar object sounds, human voices and their respective low-level control sounds. Sighted participants were additionally tested when viewing pictures of faces, objects and phase-scrambled control pictures. In both early blind and sighted, a double dissociation was evidenced in bilateral auditory cortices between responses to voices and object sounds: voices elicited categorical responses in bilateral superior temporal sulci while object sounds elicited categorical responses along the lateral fissure bilaterally, including the primary auditory cortex and planum temporale. Outside of the auditory regions, object sounds additionally elicited categorical responses in left lateral and ventral occipito-temporal regions in both groups. These regions also showed response preference for images of objects in the sighted, thus suggesting a functional specialization in these regions that is independent of sensory input and visual experience. Between-group comparisons revealed that only in the blind group, categorical responses to object sounds extended more posteriorly into the occipital cortex. Functional connectivity analyses evidenced a selective increase in the functional coupling between these reorganized regions and regions of the ventral occipito-temporal cortex in the early blind. In contrast, vocal sounds did not elicit preferential responses in the occipital cortex in either group. Nevertheless, enhanced voice-selective connectivity between the left temporal voice area and the right fusiform gyrus were found in the blind. Altogether, these findings suggest that separate auditory categories are not equipotent in driving selective auditory recruitment of occipito-temporal regions in the absence of developmental vision, highlighting domain-region constraints on the expression of crossmodal plasticity.
