Vocalic transitions as markers of speech acoustic changes with STN-DBS in Parkinson's Disease

Purpose Deep Brain Stimulation of the subthalamic nucleus (STN-DBS) effectively treats cardinal symptoms of idiopathic Parkinson's disease (PD) that cannot be satisfactorily managed with medication. Research is equivocal regarding speech changes associated with STN-DBS. This study investigated the impact of STN-DBS on vocalic transitions and the relationship to intelligibility. Methods Eight Quebec-French speakers with PD and eight healthy controls participated. The slope of the second formant frequency (F2 slope) for glides was obtained. Locus equations (LEs) were calculated to capture vocalic transitions in consonant-vowel sequences. A visual analog scale was used to obtain judgments of intelligibility. Measures for the PD group were obtained both On and Off stimulation. Results F2 slopes and LEs differed among groups, but there were no systematic differences for On versus Off STN-DBS. On an individual level, participants with PD exhibited heterogeneous changes with DBS stimulation. Intelligibility was significantly correlated with F2 slope. Conclusion F2 slope appears to be sensitive to articulatory impairment in PD and could be used in clinical settings to distinguish these speakers from healthy controls. However, acoustic metrics failed to identify systematic change with STN-DBS. The heterogeneity of results, as well as the clinical relevance of acoustic metrics are discussed.