Neural changes associated with speech learning in deaf children following cochlear implantation

Brain plasticity was investigated, which underlies the gaining of auditory sensory and/or auditory language in deaf children with an early onset deafness after cochlear implantation (CI) surgery. This study examined both the glucose metabolism of the brain and the auditory speech learning using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and the Central Institute of Deaf (CID) test, respectively, both before and after the CI surgery. In a within analysis comparing the pre-CI and the post-CI PET results, CI itself resulted in an increase in the glucose metabolism in the medial visual cortex, the bilateral thalamus, and the posterior cingulate. Compared with the normal hearing controls, the brain activity of the deaf children was greater in the medial visual cortex and bilateral occipito-parietal junctions after the CI. The better speech perception ability was associated with increases in activity in the higher visual areas such as middle occipito-temporal junction (hMT/V5) and posterior inferior temporal region (BA 21/37) in the left hemisphere and associated with decreases in activity in the right inferior parieto-dorsal prefrontal region. These findings suggest that the speech learning resulted in a greater demand of the visual and visuospatial processings subserved by the early visual cortex and parietal cortices. However, only those deaf children who successfully learned the auditory language after CI used more visual motion perception for mouth movement in the left hMT/V5 region and less somatosensory function in the right parieto-frontal region.