Sentence comprehension in Lewy body diseases: a functional magnetic resonance imaging study

Lewy body diseases, including Parkinson's disease and dementia with Lewy bodies, often involve mild cognitive impairment at diagnosis (mild cognitive impairment with Lewy bodies (MCI-LB). Language dysfunction in MCI-LB patients is often unrecognized. This study aimed to assess syntactic comprehension deficits in MCI-LB patients and to explore their neural correlates. A total of 25 MCI-LB patients (mean ± sd: 72 ± 5.6 years old, 10 women) and 25 healthy controls (HC, mean ± sd: 66 ± 4.0 years old, 12 women) performed task functional MRI Test of Sentence Comprehension (ToSC). Functional connectivity was analysed using psychophysiological interaction (PPI) method, focusing on the striatum and language networks. MCI-LB patients had lower ToSC scores than HC (MCI-LB: 74.7 ± 15.7, HC: 88.5 ± 9.0, P < 0.001) and their PPI analysis revealed decreased connectivity from the striatum to the cuneus, precuneus, and left supramarginal gyrus, and reduced connectivity particularly in the dorsal pathway during noncanonical (syntactically more complex) sentence processing. Taken together, in this cross-sectional study MCI-LB patients showed impaired sentence comprehension related to decreased subcortical-cortical and dorsal language network connectivity. Specific changes in frontotemporal connectivity in MCI-LB might be a promising indicator of language related cognitive impairment in these a-synucleinopathies.