Signed and spoken language perception studied by positron emission tomography

Sign and spoken language seem to be localized in the same brain areas. They elicit similar regional cerebral blood flow (rCBF) patterns, even though sign language is dependent on spatial information. We investigated sign and spoken language perception in a group of healthy bilingual subjects. Four videotaped activation conditions were used during PET imaging: (1) sign language, (2) spoken language, (3) spoken language with mouth covered, and(4) spoken language on a sound track while showing a motionless face. Spoken language (condition 4) activated significantly the perisylvian cortex(Brodmann areas 22 and 43) bilaterally. Sign language activated the visual association areas (Brodmann areas 37 and 19) but did not selectively activate parietal regions. A reciprocal relationship was observed between the level of activation in visual language perception areas and that in auditory perception areas. We conclude that when healthy bilingual subjects use the visual route for sign language perception, the functional anatomy overlaps that of language processing containing both auditory and visual components.