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Genotypic differences in speech and regional brain activity in hereditary ataxia
John J. Sidtis and Christopher M. Gomez

The identification of genotypic subgroups in ataxia may aid our understanding motor speech disorders. The speech produced during functional imaging with PET in 14 spinocerebellar ataxia type 1 (SCA1) and 5 spinocerebellar ataxia type 6 (SCA6) subjects was studied. Subjects repeated the syllables /pa, ta, ka/ as quickly as possible. Voice onset time (VOT) was determined. There was an interaction between place of articulation and ataxic group with significantly longer /ka/ VOT in SCA6 than SCA1 subjects. A discriminant function analysis compared the two groups to normal speakers identifying two significant discriminators, one correlated with mean VOT, the second with VOT variability. Linear regression identified the brain regions that predicted subjects’ scores on those functions. The mean VOT function was predicted by activity in the right cerebellum and left thalamus while the VOT variability function was predicted by activity in the right cerebellum and right superior temporal gyrus. Two different genotypes of hereditary ataxia with comparable levels of dysarthria differed with respect to VOT characteristics, which may reflect functional differences in the activity of the cerebellum, thalamus and superior temporal gyrus suggesting both motor and auditory contributions to speech production. The integration of performance measures with functional image analysis in different speaker populations may provide a more accurate model of motor speech control.

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