Impact of early deafness and early exposure to sign language on the cerebral organization for motion processing

This functional magnetic resonance imaging study investigated the impact of early auditory deprivation and/or use of a visuospatial language [American sign language (ASL)] on the organization of neural systems important in vi sual motion processing by comparing hearing controls with deaf and hearing native signers. Participants monitored moving flowfields under different co nditions of spatial and featural attention. Recruitment of the motion-selec tive area MT-MST in hearing controls was observed to be greater when attent ion was directed centrally and when the task was to detect motion features, confirming previous reports that the motion network is selectively modulat ed by different aspects of attention. More importantly, we observed marked differences in the recruitment of motion-related areas as a function of ear ly experience. First, the lateralization of MT-MST was found to shift towar d the left hemisphere in early signers, suggesting that early exposure to A SL leads to a greater reliance on the left MT-MST. Second, whereas the two hearing populations displayed more MT-MST activation under central than per ipheral attention, the opposite pattern was observed in deaf signers, indic ating enhanced recruitment of MT-MST during peripheral attention after earl y deafness. Third, deaf signers, but neither of the hearing populations, di splayed increased activation of the posterior parietal cortex, supporting t he view that parietal functions are modified after early auditory deprivati on. Finally, only in deaf signers did attention to motion result in enhance d recruitment of the posterior superior temporal sulcus, establishing for t he first time in humans that this polymodal area is modified after early se nsory deprivation. Together these results highlight the functional and regi onal specificity of neuroplasticity in humans.