Visual hallucinations and illusions in Parkinson’s disease: the role of ocular pathology

Visual Hallucinations (VH) are a common non-motor symptom of Parkinson’s Disease (PD) and the Lewy body dementias (LBD) of Parkinson's disease with dementia (PDD) and Dementia with Lewy Bodies (DLB). The origin of VH in PD and LBD is debated: earlier studies considered a number of different possible mechanisms underlying VH including visual disorders, Rapid Eye Movement (REM) Sleep Intrusions, dysfunctions of top down or bottom up visual pathways, and neurotransmitter imbalance.More recently newer hypotheses introduce, among the possible mechanisms of VH, the role of attention networks (ventral and dorsal) and of the Default Mode Network (DMN) a network that is inhibited during attentional tasks and becomes active during rest and self referential imagery.Persistent DMN activity during active tasks with dysfunctional imbalance of dorsal and ventral attentional networks represents a new hypothesis on the mechanism of VH.We review the different methods used to classify VH and discuss reports supporting or challenging the different hypothetical mechanisms of VH.

Download Full-text

Exploring Bottom-Up Visual Processing and Visual Hallucinations in Parkinson’s Disease with Dementia

10.1101/2020.06.28.20142042 ◽

2020 ◽

Author(s):

Nicholas Murphy ◽

Alison Killen ◽

Sara Graziadio ◽

Lynn Rochester ◽

Michael Firbank ◽

...

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Executive Control ◽

Visual Processing ◽

Common Symptom ◽

Visual Hallucinations ◽

Bottom Up ◽

Parkinson’S Disease With Dementia ◽

System Physiology

AbstractVisual hallucinations (VH) are a common symptom of Parkinson’s disease with dementia (PDD), affecting up to 65% of cases. Integrative models of their etiology posit that a decline in executive control of the visuo-perceptual system is a primary mechanism of VH generation. The role of bottom-up processing in the manifestation of VH in this condition is still not clear. Here we compared amplitude and latency patterns of reversal visual evoked potentials (VEPs) in healthy controls (n=21) and PDD patients (n = 34) with a range of VH severities. PDD patients showed increased N2 latency relative to controls, but patients reporting complex VH (n=17) did not demonstrate any relationship between VEP measurements and their hallucination severity as measured on the neuropsychiatric inventory hallucinations subscale (NPIHal) score. Our VEP findings support previous reports of declining visual system physiology in PDD. However, no notable major relationships between the integrity of the visual pathway and VH were found.

Download Full-text