Objective: To investigate the long-term effects of repeated home-based transcranial direct current stimulation (tDCS) on language production in patients with Parkinson’s disease (PD).

Background: Language production deficit is a common non-motor symptom of PD and may affect lexical richness, discourse organization, and syntactic complexity. Non-invasive brain stimulation techniques such as tDCS can modulate cortical plasticity in language-related areas.

Method: A randomized parallel-group sham-controlled study is ongoing. Althogether 29 PD patients, mean age 71.4 ± 6.7 years in the real stimulation group (n=15) and 71.3 ± 5.9 in the sham stimulation group (n=14) have completed the study so far. Participants received 10 home-based tDCS sessions (2 mA, 20 minutes) targeting the left inferior frontal gyrus (IFG). Assessments were conducted at baseline (T0), after 10 tDCS sessions (T1), and at 8-week follow-up (T2).

Speech production was evaluated using the Cookie Theft Picture Description task, focusing on different linguistic and temporal domains and their characteristic measures. Effects of age, sex, and education were regressed out using linear regression trained on baseline data and applied to all sessions. Mann–Whitney U tests were used for pairwise comparisons (T0–T1, T0–T2, T1–T2) and Kruskal–Wallis tests for comparisons across T0, T1, and T2.

Results: In the picture description task, the real stimulation PD group showed significant changes relative to baseline while no such changes were observed in the sham stimulation PD group. The proportion of subordinate clauses increased after the stimulation (T1 vs T0), reflecting higher syntactic complexity. At follow-up (T2 vs T0), the proportion of longer words (≥3 syllables) increased, indicating greater lexical complexity. The standard deviation of syllables per word also increased, suggesting greater variability in the word length. The proportion of longer words relative to total speech duration increased.

Conclusion: Repeated home-based tDCS targeting the left IFG was associated with increased linguistic richness in spontaneous speech production in PD. Patients receiving real stimulation produced more complex and variable vocabulary and more elaborated sentence structures. These findings suggest that home-based tDCS may represent a promising supportive approach for improving language production in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/long-term-effects-of-repeated-home-based-tdcs-on-language-production-in-parkinsons-disease/