Neural correlates of minor hallucinations in non-demented patients with Parkinson's disease

Background: Hallucinations are a frequent and severe complication in Parkinson's disease (PD). Minor hallucinations are generally not disturbing, but likely progress to well-structured hallucinations with loss of insight and a great impact on quality of life. Knowledge on the neural bases of minor hallucinations may help to describe those systems associated with the early development of psychotic phenomena in PD. In this study, we aimed to identify the pattern of structural brain alterations associated with minor hallucinations in PD by using voxel-based morphometry (VBM).

Methods: We prospectively collected a sample of 46 non-demented PD patients, with (N = 17) and without (n = 29) minor hallucinations (passage and/or presence hallucinations), and 15 healthy controls. Groups were matched for age, education and global cognitive function. Presence and type of minor psychotic phenomena was assessed by the new MDS-UPDRS. Three dimensional T1-weighted MRI images were acquired with a 1.5 T magnet, and analyzed using optimized VBM.

Results: Compared to controls, PD with minor hallucinations (PD-mH) showed reduced gray matter volume bilaterally in different areas of the dorsal visual stream, and in functionally related midbrain and cerebellar structures. Additionally, bilateral gray matter volume increases were observed in the PD-mH group in limbic and paralimbic regions.

Conclusions: Our data support a major role of the dorsal visual stream in the genesis of minor hallucinations in PD, reinforcing the importance of posterior cortical regions for the development of cognitive and psychiatric complications in PD.