Individuals with early- and late-onset deafness showed different functional and morphological brain changes, but white matter alterations in both deaf groups still need to be elucidated. This study aimed to investigate changes in white matter integrity and white matter anatomical connectivity in both early- and late-onset deaf groups compared with hearing group.
Diffusion tensor imaging data from 7 early-onset deaf (50.7 ± 6.5 years), 11 late-onset deaf (50.9 ± 12.3 years), and 9 hearing adults (48.9 ± 9.5 years) were preprocessed using FSL software. To find changes in white matter integrity, tract-based spatial statistics was used, which implemented on FSL software. Fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD) were calculated and compared among the groups with age as a nuisance variable. To find out the effect of onset age or duration of deafness to the white matter integrity, onset-age or duration of deafness was treated as a variable of interest in the general linear model implemented on tract-based spatial statistics. White matter connectivity was constructed by a deterministic tractography and compared among the groups.
In comparison to the hearing group, the early-onset deaf group did not show any significant changes but the late-onset deaf group showed decreased FA and increased RD in the several white matter areas. AD in the late-onset deaf group was not significantly different compared with the hearing group. The regions included the corpus callosum, posterior and superior corona radiata, internal capsule, posterior thalamic radiation, superior longitudinal fasciculus, and tapetum of the right hemisphere. Increased RD was also additionally observed in the right external capsule, fornix, and cerebral peduncle. The onset age or duration of deafness was not significantly correlated with the white matter integrity in the early-onset deaf group. In contrast, the onset age showed a significantly positive correlation with the RD, and a negative correlation with the FA, in the late-onset deaf group. The correlated white matter areas were also similar to the findings of comparison with the hearing group. In comparison to the hearing group, the early-onset deaf group did not show altered white matter connectivity, while the late-onset deaf group showed decreased white matter connectivity in between the right lingual and hippocampal areas.
The present results suggest that late-onset deaf adults showed decreased FA and increased RD, and early-onset deaf adults showed no difference compared with the hearing group. In the late-onset deaf adults, onset-age showed a significantly positive correlation with RD and negative correlation with FA. Duration of deafness was not significantly correlated with the changes. Increased RD indicating demyelination occurred in the brain, and the changes were not limited to the auditory cortex but expanded to almost whole brain areas, suggesting significant effect of auditory deprivation on the brain later in life. The altered white matter connectivity in between the right limbic-occipital areas observed in the late-onset deaf group might be caused by altered language functions after auditory deprivation. Future studies are necessary incorporating functional and anatomical aspects of the brain changes in deaf group.