Cortical connectivity of cholinergic basal forebrain in Parkinson's disease with mild cognitive impairment.

Background: Cholinergic basal forebrain (BF) pathology is a hallmark of Parkinson's disease (PD) with mild cognitive impairment (PD-MCI). Assessment of functional connectivity (FC) of different cholinergic BF nuclei may deepen the understanding of PD-MCI pathogenesis. Methods: Seed-based FC analysis was performed with bilateral medial septal nucleus, the nucleus of the vertical limb of the diagonal band, nucleus of the horizontal limb of the diagonal band (Ch1-3), and the nucleus basalis of Meynert (NBM/Ch4) to explore the BF functional alterations in different frequency bands. Correlations between FC values of abnormal regions and scores of cognitive domains and depression in the PD group were also assessed. Results: For the right Ch4, in the conventional frequency band, the PD-MCI group exhibited lower FC values in the right middle cingulate and paracingulate gyri, middle frontal gyrus, left inferior parietal gyrus, and superior frontal gyrus compared with healthy controls (HC), and in the left calcarine fissure and surrounding cortex compared with PD with normal cognition (PD-NC). For the slow 4 subbands, the PD-MCI group showed significantly lower FC values in the left putamen, middle frontal gyrus, right middle frontal gyrus, and precuneus compared with HC, and in right middle frontal gyrus cingulate and paracingulate gyri compared with the PD-NC group. For the slow 5 subbands, the PD-MCI group showed increased FC values in the right calcarine fissure and surrounding cortex, and left cerebellum. For the left Ch1-3, FC values in the right middle cingulate and paracingulate gyri were lower in patients with PD-MCI than in the PD-NC group in slow 4 subbands. Furthermore, altered FC values in the cortical regions for Ch4 seed were possibly correlated with depression and different cognitive domain scores. Conclusions: The study identified an imbalanced association between different cholinergic BF nuclei and cortical regions in patients with PD-MCI, and showed that FC changes are frequency-specific, which may provide new insights into functional alterations within the cholinergic system in cognitive impairment associated with PD.