Objective: To assess levodopa-induced changes in fMRI signal in areas involved in speech production (ROIs) in PD. Evaluate association between these changes and changes in acoustic parameters describing articulation and prosody.

Background: Hypokinetic dysarthria (HD) is one of the difficult-to-treat symptoms affecting quality of life in patients with Parkinson’s disease (PD). While levodopa may partially alleviate some symptoms of HD in PD, neural correlates of these effects are not fully understood.

Method: A total of 20 patients with PD in their OFF and ON dopaminergic condition after administration of a single dose of levodopa, and 25 aged matched healthy controls (HC) were recruited. Participants underwent a speech task fMRI and recordings from a scanner were analysed offline using an acoustic analysis of articulatory and prosodic feature previously described.
Between-groups analysis was performed using task-induced fMRI data from ROIs in the dorsal language pathway bilaterally based on the literature. In the PD group, changes in task-induced BOLD signal increases between OFF and ON dopaminergic conditions were correlated with changes in acoustic parameters of speech.

Results: We observed no significant differences in acoustic parameters due to acute levodopa administration in the PD group. Patients showed significantly lower task-induced MRI signal increases after levodopa administration in the left ventral thalamus as compared to the OFF dopaminergic condition (p = 0.0033). The changes in thalamic activation were associated with changes in pitch variation (R= 0.67, p = 0.006), and with changes in speech initiation time (R= 0.56, p = 0.025).

Conclusion: The results of our study show that levodopa induces focusing effects on speech-induced activation within the left thalamus on individual level. The thalamus plays an important role in modulating the symptoms of hypokinetic dysarthria due to dopaminergic medication.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-effect-of-levodopa-on-speech-in-patients-with-parkinsons-disease/