Subcortical contributions to language deficits in Parkinson's disease.

INTRODUCTION: Dopaminergic neurons degeneration in Parkinson’s disease (PD) disrupts the basal ganglia (BG) network, leading to both motor and cognitive impairments, including language processing difficulties. Particularly, semantic fluency is affected due to BG dysfunction and impaired lexical-semantic integration. This study examines the association between the BG dopaminergic function and semantic fluency in PD patients, providing further insight into the neural mechanisms underlying language deficits. MATERIALS AND METHODS: All data were obtained from the Parkinson’s Progression Markers Initiative (PPMI) at baseline for both healthy controls (HCs) and PD patients and at a 4-year follow-up for PD patients. A partial correlation was conducted to examine the relationship between DaTScan striatal binding ratio (SBR) and semantic fluency at baseline and after four years, along with the changes in these measures over the 4 years. RESULTS: Semantic fluency and DaTScan SBR scores at baseline showed no correlation in HCs or PD patients. However, by the 4-year follow-up, a positive correlation emerged between DaTScan SBR in the bilateral putamen and semantic fluency performance in the animal category. Additionally, DaTScan SBR in the right putamen was linked to the total semantic fluency score. No significant correlation was found between changes in these measures over the 4 years. CONCLUSION: Our study found that semantic fluency impairments emerge early in PD and is linked to dopaminergic activity in bilateral putamens at later stages. These results highlight the role of frontostriatal circuits, especially the putamen, in category-based verbal retrieval, demonstrating subcortical structures’ contribution to language function in PD.