Altered Cross-Modal Processing in the Primary Auditory Cortex of Congenitally Deaf Adults: A Visual-Somatosensory fMRI Study with a Double-Flash Illusion

TLDR

The developing brain uses statistical correlations in input to guide functional and structural changes, and experience shapes brain development throughout life, though neuroplasticity varies across systems. The study investigates how congenital deafness influences cross‑modal neuroplasticity in primary auditory cortex. The authors used fMRI to measure signal changes in visual, somatosensory, and bimodal stimuli across anatomically defined subregions of Heschl's gyrus in congenitally deaf adults. In deaf participants, somatosensory and bimodal stimuli evoked greater fMRI responses in Heschl's gyrus than in hearing controls, visual responses were larger but weaker than somatosensory, and the altered cross‑modal organization predicted susceptibility to a double‑flash illusion, demonstrating that congenital deafness changes how vision and somatosensation are processed in primary auditory cortex.

Abstract

The developing brain responds to the environment by using statistical correlations in input to guide functional and structural changes—that is, the brain displays neuroplasticity. Experience shapes brain development throughout life, but neuroplasticity is variable from one brain system to another. How does the early loss of a sensory modality affect this complex process? We examined cross-modal neuroplasticity in anatomically defined subregions of Heschl9s gyrus, the site of human primary auditory cortex, in congenitally deaf humans by measuring the fMRI signal change in response to spatially coregistered visual, somatosensory, and bimodal stimuli. In the deaf Heschl9s gyrus, signal change was greater for somatosensory and bimodal stimuli than that of hearing participants. Visual responses in Heschl9s gyrus, larger in deaf than hearing, were smaller than those elicited by somatosensory stimulation. In contrast to Heschl9s gyrus, in the superior-temporal cortex visual signal was comparable to somatosensory signal. In addition, deaf adults perceived bimodal stimuli differently; in contrast to hearing adults, they were susceptible to a double-flash visual illusion induced by two touches to the face. Somatosensory and bimodal signal change in rostrolateral Heschl9s gyrus predicted the strength of the visual illusion in the deaf adults in line with the interpretation that the illusion is a functional consequence of the altered cross-modal organization observed in deaf auditory cortex. Our results demonstrate that congenital and profound deafness alters how vision and somatosensation are processed in primary auditory cortex.