Multimodal Investigation of Visual Hallucinations in Parkinson's Disease

Abstract

Visual hallucinations (VH) are a common symptom of Parkinson’s disease (PD) and significantly contribute to the burden of the disease. Our understanding of the pathophysiology is limited, due in part to the inherent difficulty in objectively studying the subjective experience. In this thesis, a literature review first summarises leading mechanistic models of VH in PD. This is followed by a multimodal set of empirical studies, with the following overarching aims:

1- To explore whether a targeted caregiver questionnaire can enhance reliability of symptom reporting, thereby improving detection and monitoring for future research

2- To use neuropsychological testing to identify deficits predating the onset of VH, establishing a cognitive profile that predisposes to the hallucinatory trait

3- To analyse EEG recordings during surrogate visual phenomena akin to VH, to directly interrogate brain activity during the hallucinatory state.

The first study showed that carers can provide additional information on the presence and severity of VH via questionnaire, although reporting rates were highest from patients themselves. The second study identified a distinct neuropsychological profile of patients at risk of developing VH in the future, revealing deficits in psychomotor speed, executive functioning, reaction time and attention. The final study, utilising EEG in conjunction with the Bistable Percept Paradigm, demonstrated that early frontal and late posterior activity are temporally associated with visual misperception events.

This research has implications for improving the identification of patients with VH, revealing the neuropsychological traits which may predispose to their development, and electrophysiological signatures underlying the hallucinating state. This thesis thereby significantly contributes to the body of research investigating VH in PD by enhancing our ability to study the phenomenon, and by advancing our understanding of the pathophysiology involved.