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Study Identifies Key Brain Network Dysfunction in Parkinson’s Disease Hallucinations

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A recent study published in the journal Movement Disorders has provided significant insights into the neural mechanisms underlying minor and well-structured major hallucinations in Parkinson’s disease (PD). Researchers from various South Korean institutions conducted the study, which used resting-state functional magnetic resonance imaging (rs-fMRI) to look into functional brain networks in Parkinson’s disease patients who were experiencing various types of hallucinations.

Hallucinations are a common symptom in Parkinson’s disease, affecting up to 60% of patients during the course of the disease. These hallucinations can range from minor (mHs) to well-structured major hallucinations (MHs). The study aimed to explore the resting-state networks (RSNs) involved in patients with PD without hallucinations (PD-nH), with minor hallucinations (PD-mH), and with major hallucinations (PD-MH). The primary objective was to identify specific network alterations that might differentiate these groups and contribute to the understanding of hallucination progression in PD.

The study enrolled 73 patients with Parkinson’s disease, categorised into three groups: 27 without hallucinations, 23 with minor hallucinations, and 23 with major hallucinations. They used seed-based functional connectivity analyses to look into RSNs connected to hallucinations. These networks included the default mode network (DMN), the executive control network (ECN), the dorsal attention network (DAN), the ventral attention network (VAN), and the visual network (VN). Cognitive function and RSN connectivity were compared across the three groups, with a focus on inter-network connectivity within each group.

The results revealed several significant differences in both cognitive function and network connectivity among the groups. Patients in the PD-MH group exhibited lower test scores for attention and visuospatial functions compared to the other groups. This group also had less connectivity in the DAN’s right intracalcarine cortex, which suggests a possible key factor in how minor hallucinations become major ones in PD.

Both the PD-mH and PD-MH groups displayed higher connectivity in the left orbitofrontal cortex within the DMN compared to the PD-nH group. In other areas, though, they were less connected. For example, the right middle frontal gyrus (MFG) in the ECN, the precuneus cortex in the VAN, and the right middle temporal gyrus and precuneus cortex in the DAN.

Inter-network connectivity analyses showed distinct patterns among the groups. The PD-mH and PD-MH groups demonstrated different inter-network connectivity between the five RSNs, particularly regarding the DAN. This network appears to play a crucial role in the progression from minor to major hallucinations, with dysfunction in the DAN potentially being a key factor.

The findings of this study underscore the importance of the DAN in the development and progression of hallucinations in Parkinson’s disease. The researchers concluded that DAN dysfunction might be a critical factor in the transition from minor to major hallucinations. This insight provides a deeper understanding of the pathophysiology of hallucinations in PD and could inform future therapeutic strategies aimed at managing these symptoms.

The study also supports the theory that minor hallucinations might be an early and less severe manifestation of the same underlying network dysfunctions that cause major hallucinations. By finding specific changes in networks that are linked to different kinds of hallucinations, this study opens the door to possibly creating targeted treatments that can stop the worsening of hallucinatory symptoms in Parkinson’s disease.

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