Visual Hallucinations in Parkinsonism Disorders: Overview of Predominant Theoretical Models

Non-motor symptomatology of Parkinson’s Disease and related conditions is not receiving as much attention in the academic literature as the movement pathologies classically associated with Parkinsonism, although it leads to a significantly impaired quality of life (Pfeiffer, 2016). Visual hallucinations (VH) in particular are a strong predictor of nursing home placement and subsequent mortality (Goetz & Stebbins, 1995; Pfeiffer, 2016). The focus of this thesis is a bibliographic analysis of the theoretical frameworks which aim to explain the genesis and treatment of VH, present in the scientific and clinical discourse. Contributions to the topic of VH come from a plethora of perspectives, including pharmacological, cognitive, psychoanalytical, computational, and phenomenological, among others. Given this abundance of approaches, a successful theoretical model should be flexible and considerate of all aspects of the topic at hand. For this reason, most attention in this thesis is given to the Perception and Attention model, which seems the most well-versed in the current research literature, but leaves room for improvement. Strengths and weaknesses of the PAD and other theories are discussed. A historical account, starting from the beginning of the twentieth century, of the empirical progress on the topic is described and an overview of the predominant contemporary models is presented as the main body of the text. The aim of this paper was to delineate the various theoretical formulations for VH in visual neuropsychiatry and related fields, with an emphasis on Parkinsonism disorders, and to give a unified, up-to-date report of the current research trends. Proposals for future experimental work are outlined in the conclusion of the thesis.