Resting activity in visual and corticostriatal pathways in Parkinson's disease with hallucinations.

Background: Visual hallucinations are an important non-motor complication of Parkinson's disease (PD) and carry a negative prognosis. Their biological basis is uncertain, but may relate to the activity of resting state networks in brain. We therefore aimed to investigate functional activity of brain in patients with visual hallucinations (PDVH) in resting state compared to patients without hallucinations (PDnonVH) and a healthy control group (HC).

Methods: Resting state functional MRI was acquired and the primary analysis compared the amplitude of low-frequency fluctuations (ALFF) across groups. This informed a secondary analysis, in the PD groups only, comparing functional connectivity between a 'seed' region in the occipital lobe and the rest of the brain.

Results: Individuals with PDVH showed lower ALFF in bilateral lingual gyrus and cuneus and greater ALFF in temporo-parietal regions, medial temporal gyrus and cerebellum than PDnonVH and HC. PDnonVH also had lower ALFF in occipitoparietal region and greater ALFF in medial temporal gyrus, temporo-parietal and cerebellum regions than HC. Functional connectivity analysis revealed that, although both PD groups had lower occipital functional connectivity relative to the HC group, occipital - corticostriatal connectivity was significantly higher in those with PDVH compared with PDnonVH.

Conclusion: Our study reveals widespread hemodynamic alterations in PD. However, within a functionally abnormal occipital lobe, those with PDVH have even lower ALFF than non-hallucinators, but have higher occipital functional connectivity with cortical-striatal regions. These findings suggest disruption of pathways underpinning both primary visual perceptual and intrinsic visual integration may contribute to visual hallucinations in PD.