Voice and fluency changes as a function of speech task and deep brain stimulation

Purpose: Speaking, which naturally occurs in different modes or "tasks" such as conversation and repetition, relies on intact basal ganglia nuclei. Recent studies suggest that voice and fluency parameters are differentially affected by speech task. In this study, the authors examine the effects of subcortical functionality on voice and fluency, comparing measures obtained from spontaneous and matched repeated speech samples. Method: Subjects with Parkinson's disease who were being treated with bilateral deep brain stimulation (DBS) of the subthalamic nuclei were tested with stimulators ON and OFF. Results: The study found that a voice measure, harmonic to noise ratio, is improved in repetition and in the DBS-ON condition and that dysfluencies are more plentiful in conversation with little or variable influence of DBS condition. Conclusions: These findings suggest that voice and fluency are differentially affected by DBS treatment and that task conditions, interacting with subcortical functionality, influence motor speech performance.