Neural Systems Underlying Sign Language Production

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DESCRIPTION (provided by applicant): Very little is known about the neural correlates of language production in congenitally deaf individuals who use sign language as their primary and preferred means of communication. The major goals of this project are (a) to identify the neural systems underlying the production of linguistic structures that are unique to sign language (i.e., classifier constructions that express location and motion via the iconic use of signing space), (b) to identify the neural systems that support sign communication versus gestural communication (i.e., pantomime), (c) to identify the neural systems that support phonological processing in a soundless language, and (d) to identify macroscopic variations in neuroanatomy associated with deafness or with lifelong signing. To investigate whether deafness and/or use of a signed language affect the neural systems underlying sign language production, a series of [15O] H20 PET experiments will be conducted with deaf and hearing native ASL signers. MR and PET imaging will be accomplished in collaboration with Dr Thomas Grabowski and colleagues at the University of Iowa. The experiments will test several specific predictions. We predict that the production of spatial classifier constructions engages parietal cortices that sub serve a spatial-motoric transformation from a visual to a body-centered manual representation. We predict that signing and pantomime will both engage fronto-parietal regions, but these regions will be non-identical and signing will additionally engage temporal lobe structures. We make the surprising prediction that the phonological encoding of sign language engages the same neural systems as spoken language (specifically, Broca's area and left superior temporal cortex). Finally, we predict that auditory deprivation from birth affects the size and morphology of the insula, but not Broca's area, and that life-long signing affects the size of the anterior sector of the corpus callosum and of the hand knob region within primary motor cortex. These anatomical predictions will be investigated using MRI data from deaf and hearing native signers and from hearing nonsigners. In addition to contributing to a better understanding of the neural basis of sign language (and therefore of language in general), the findings will be help improve diagnosis and develop rehabilitation strategies for deaf patients with communicative disorders.