Acceleration of syllable repetition in Parkinson's disease is more prominent in the left-side dominant patients

Background: In Parkinson's disease (PD), abnormalities of speech rate have been observed in spontaneous speech, reading tasks and syllable repetition tasks. Impaired temporal speech patterns have been contributed to dysfunctional basal ganglia circuits, but little is known about a possible differential role of right and left basal ganglia concerning speech production, although neurodegeneration in PD typically follows an asymmetrical pattern. The aim of our study was to reveal a possible influence of lateralized basal ganglia dysfunction on speech timing in PD. Patients and methods: 60 patients with PD (30 with predominant symptoms on the left-side PD_L and 30 with predominant symptoms on the right side PD_R) and 40 healthy controls were tested. Participants had to repeat a single syllable in a self chosen steady pace. Additionally, the participants performed a reading task in order to measure speaking rate related to connected speech. Results: Syllable repetition showed a significant instability in both PD groups as compared to controls. However, the PD_L group performed in a much higher pace with further significant pace acceleration in the course of the syllable repetition task. This pattern showed a further correlation to axial motor symptoms. No correlations were seen between parameters of syllable repetition and the reading task. Conclusions: Lateralization of basal ganglia dysfunction in PD seems to differentially impact the stability of spontaneous syllable repetition pace. Our data suggest a crucial role of the right basal ganglia in the maintenance of isochronous speech rhythms at least in patients with additional axial motor symptoms. © 2011 Elsevier Ltd.