PURPOSE: The present study was designed to investigate the neural correlates of German Sign Language (Deutsche Gebärdensprache; DGS) processing. In particular, was expected the impact of the visuo-spatial mode in sign language on underlying neural networks compared to the impact of the interpretation of linguistic information.
METHODS: For this purpose, two groups of participants took part in a functional MRI study at 3 Tesla. One group consisted of prelingually deafened users of DGS, the other group of hearing non-signers naïve to sign language. The two groups were presented with identical video sequences comprising DGS sentences in form of dialoges. To account for substantial interindividual anatomical variability observed in the group of deaf participants, the brain responses in the two groups of subjects were analyzed with two different procedures.
RESULTS: Results from a multi-subject averaging approach were contrasted with an analysis, which can account for the considerable inter-individual variability of gross anatomical landmarks. The anatomy-based approach indicated that individuals' responses to proper DGS processing was tied up with a leftward asymmetry in the dorsolateral prefrontal cortex, anterior and middle temporal gyrus, and visual association cortices. In contrast, standard multi-subject averaging of deaf individuals during DGS perception revealed a less lateralized peri- and extrasylvian network. Furthermore, voxel-based analyses of the brains' morphometry evidenced a white-matter deficit in the left posterior longitudinal and inferior uncinate fasciculi and a steeper slope of the posterior part of the left Sylvian Fissure (SF) in the deaf individuals.
CONCLUSION: These findings may imply that the cerebral anatomy of deaf individuals has undergone structural changes as a function of monomodal visual sign language perception during childhood and adolescence.