Objective: To describe the patterns of brain functional changes when visual hallucinations (VH) occur in patients with Parkinson’s disease (PD).

Background: ​With disease progression, PD patients may have chronic visual hallucinations (VH). They often cause distress for the patient and their caregiver. The mechanisms behind chronic VH in PD remain largely unknown, namely because it is difficult to capture hallucination events. Up to now, only one case-report has been published. It revealed a disorganization of the occipital-frontal circuits, giving rise to misinterpretation of visual perceptions.

Methods: Nine PD patients participated in the study. All experienced frequent and chronic VH (> 10/day). Patients with severe cognitive decline (MMSE<18) were excluded. Psychotropic and anti-parkinsonian medications were stable during the last 30 days before inclusion. Patients were scanned during ON/OFF hallucinatory states in a 3T MRI scanner (Philips Achieva). High-resolution 3D T1-weighted images were acquired with a magnetization-prepared gradient echo sequence. Resting-state functional imaging (fMRI) was performed with a T2*-weighted EPI sequence lasting 10 min. Patients were required to remain quiet, stay awake and close their eyes. Data were analyzed in reference to the two-step method (1), i.e., including (i) a multivariate data-driven analysis of per-hallucinatory fMRI data (ICA), and (ii) selection of the components of interest based on a post-fMRI interview;

Results: Data from four PD patients with and three without VH were analyzed. Data from two patients with VH had to be discarded due to motion artifacts. The phenomenology of VH ranged from visual spots to distorting faces. At the individual level, several VH-related components of interest were identified and integrated into a second-level analysis. Using a random-effects self-organizing-group ICA, we evidenced increased connectivity in visual networks concomitant to VH, encompassing V2, V3, and the fusiform gyri bilaterally. Interestingly, the stability of the default-mode network (DMN) was found positively correlated with VH severity (Spearman’s​ rho=0.77, p=0.05);

Conclusions: By using the two-step method (that does not need online self-report), we showed that VH are associated with functional changes in associative visual cortices. Contrasting with previous results in schizophrenia, VH in PD patients were found associated with strengthened DMN spatial stability.

References: 1. Leroy A. et al. fMRI capture of auditory hallucinations: validation of the two-steps method. Hum Brain Mapp 2017, 38(10): 4966-79.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/what-can-we-learn-from-fmri-capture-of-visual-hallucinations-in-parkinsons-disease/