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Behavioural Neurology
Volume 27, Issue 4, Pages 479-493

Visual Hallucinations in PD and Lewy Body Dementias: Old and New Hypotheses

M. Onofrj,1,2 J. P. Taylor,3 D. Monaco,1,2 R. Franciotti,1 F. Anzellotti,1,2 L. Bonanni,1,2 V. Onofrj,4 and A. Thomas1,2

1Department of Neuroscience and Imaging, University G. d’Annunzio of Chieti-Pescara, Chieti, Italy
2Aging Research Center, “G. d’Annunzio” University Foundation, Chieti, Italy
3Institute for Ageing and Health, Wolfson Research Centre, Campus for Ageing and Vitality, Newcastle University, Newcastle Upon Tyne, UK
4Università del Sacre Cuore, Istituto di Radiologia, Rome, Italy

Received 10 December 2012; Accepted 10 December 2012

Copyright © 2013 Hindawi Publishing Corporation and the authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.