Language Network Disruption in Patients with Lewy Body Diseases

Background Lewy body diseases, including Parkinson’s disease and dementia with Lewy bodies, are marked by neuronal α‑synuclein aggregation, motor parkinsonism, cognitive impairment and diverse non‑motor symptoms including communication impairments. Compared to other symptoms, non‑motor communication impairments remain under-explored, especially outside English‑speaking cohorts. Objective The aim of this study was to elucidate the neural underpinnings of linguistic deficits as assessed by fMRI in Czech-speaking patients diagnosed with neuronal Lewy body disease and mild cognitive impairment (LBD-MCI). Methods Scores from the Short Neuropsychological Battery and resting‑state functional MRI data were analyzed in 26 Czech‑speaking patients with LBD‑MCI (18 Parkinson’s disease‑MCI; 8 Lewy body‑MCI) and 24 healthy controls. Analyses targeted regions of interest within the dorsal and ventral language networks. We applied graph theory metrics, within‑network connectivity and seed‑based functional connectivity analysis. Results Graph analysis revealed dorsal‑stream disruption in LBD‑MCI: reduced clustering coefficient, increased path length, and diminished node strength, each correlating with language functions; ventral‑stream topology remained intact. Within‑network analyses showed impaired connectivity across both pathways, but weaker coupling between the opercular inferior frontal gyrus and posterior superior temporal gyrus predicted behavioral scores in language functioning, further highlighting dorsal vulnerability. Seed‑based analysis identified reduced frontotemporal connectivity in the dorsal stream and decreased fronto‑occipital and temporo-cerebellar connections in the ventral stream. Conclusions LBD‑MCI is characterized particularly by network‑specific reductions in dorsal language stream efficiency and functional connectivity, underpinning syntactic and phonological processing deficits. These findings offer novel insights in the neural basis of language impairment in LBD-MCI.