Indicators of Parkinsonian Visual Hallucinations: Enhanced Beta and Gamma Coherence

Introduction: Visual hallucinations are one of the common non-motor symptoms of Parkinson’s disease. Although various theories have been proposed, the pathological mechanism is not fully understood. This study aimed to investigate spontaneous brain activity in hallucinated and non-hallucinated patients with Parkinson’s disease (PD) by using EEG and also its relevance to the behavioral and neuropsychological status of patients. Methods: A total of 30 people were included in the study: 10 hallucinated PD patients, 10 non-hallucinated PD patients, and 10 healthy controls. Spontaneous EEG data were recorded in eyes-open and eyes-closed conditions. A neuropsychological battery was used to evaluate visual and verbal memory, visuo-spatial abilities, executive functions, and behavioral/emotional status of participants. Results: The hallucinated group did not show an increase in alpha power activity in response to eye closure, although healthy controls showed a significant increase in alpha power in eyes closed condition. Parkinson’s disease patients with hallucinations showed significantly higher intra-hemispheric beta and gamma coherence and the non-hallucinated group demonstrated significantly lower inter-hemispheric alpha coherence. Additionally, Hallucinated PD patients showed higher NPI (Neuropsychiatric Inventory) scores and RBD-SQ (REM Behavior Disorder Screening Questionnaire) scores, lower motor scores (Unified Parkinson’s Disease Rating Scale – UPDRS), and a higher number of Stroop Test errors compared to non-hallucinated PD patients. Conclusion: Increased abnormal resting-state EEG activity and a tendency towards greater impairment of executive functions were seen in hallucinated PD patients. These results can be interpreted as an abnormal resting activity in cortical networks that may underlie their visual hallucinations symptoms.