Objective:  

To explore the neural correlates of Visual Hallucinations (VH) in patients with Parkinson’s disease (PD).

Background: Psychosis is one of the commonly observed non-motor symptoms of PD. It usually manifests as visual hallucinations (VH) and minor hallucinations. The neural correlates of VH are not fully understood. Early identification of PD patients at risk of developing psychosis is imperative as psychosis significantly worsens the quality of life of patients with PD.  Hence it is crucial to explore the signature alterations in neural networks in patients with PD having VH.

Methods: This study included 40 subjects with PD [ 20 with VH (PD+VH), 20 without VH (PD-VH)]. MR images were obtained for all subjects in a 3T scanner. Mini Mental Status Examination (MMSE) was done to screen for cognitive impairment and a score < 26 was set as an exclusion criteria.  Severity and stage of PD were assessed by using the Unified Parkinson’s Disease Rating Scale (UPDRS III) and the Hoen and Yahr (H&Y) scale respectively. Graph theory based analysis was used to compare the pattern of functional connectivity between the two groups.

Results: There was no significant difference in the age, duration of illness, and gender distribution between the two groups.  Comparison of the global graph metrics revealed significantly increased clustering coefficient (CC) and decreased path length in PD+VH group.  Comparison of the graph metrics of individual seeds revealed significantly higher CC in structures corresponding to several resting state networks such as default mode network (superior frontal gyrus, precuneus, inferior temporal gyrus, inferior parietal sulcus, angular gyrus), fronto-parietal network (dorsolateral and ventrolateral prefrontal cortex), and parahippocampal gyrus in PD+VH group.  PD+VH group had significantly lower clustering coefficient in the anterior cingulate cortex, which is a component of cingulo-opercular network.

Conclusions: Patients with VH have significantly higher small-worldness compared to those without VH. Several structures corresponding to the default mode network, and fronto-parietal network have a higher clustering coefficient in PD+VH group whereas the cingulo-operacular network had reduced clustering coefficient in patients with VH.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/aberrant-resting-state-functional-brain-networks-in-patients-with-parkinsons-disease-and-visual-hallucinations/