Differences in brain structure in deaf persons on MR imaging studied with voxel-based morphometry

The loss of a major sensory input early in life is known to cause alterations in neuronal connectivity and physiology at the cellular level, but effects on gross anatomy are less well understood. The purpose of this study was to compare volumetric structural brain MR imaging scans of deaf versus hearing subjects by using voxel-based morphometry (VBM). The hypothesis was that the deaf would have relative hypoplasia in the temporal lobe centers involved in hearing and speech.

T1-weighted volumetric images from 53 prelingually deaf persons and 51 control subjects were analyzed with VBM. Initial segmentations were spatially normalized, and then these deformation parameters were applied to the original images, which were again segmented. Statistic parametric mapping was then applied on a voxel-by-voxel basis to determine group differences and asymmetries.

The white matter analysis revealed a statistically significant focal deficit in the deaf persons in the left posterior superior temporal gyrus (STG), corresponding to white matter inferior to auditory cortex. Gray matter asymmetries in the deaf persons were overall similar to that in hearing persons but a focal loss of asymmetry was noted in the posterior STG white matter in the deaf persons.

These results support the hypothesis that there are gross alterations in brain anatomy as a consequence of early deafness. The white matter deficit in the posterior left superior temporal gyrus may represent hypoplasia of the auditory/speech related tracts. Hemispheric asymmetries however remain largely intact.