title: Visual hallucinations in PD and Lewy body dementias: old and new hypotheses.
abstract: 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.
authors.affiliation: Department of Neuroscience and Imaging, University G. d'Annunzio of Chieti-Pescara, Chieti, Italy Aging Research Center, "G. d'Annunzio" University Foundation, Chieti, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Onofrj
authors.forename: J P
authors.initials: JP
authors.lastname: Taylor
authors.forename: D
authors.initials: D
authors.lastname: Monaco
authors.forename: R
authors.initials: R
authors.lastname: Franciotti
authors.forename: F
authors.initials: F
authors.lastname: Anzellotti
authors.forename: L
authors.initials: L
authors.lastname: Bonanni
authors.forename: V
authors.initials: V
authors.lastname: Onofrj
authors.forename: A
authors.initials: A
authors.lastname: Thomas
mesh_terms: D001288:Attention / Q000502:physiology*; D006212:Hallucinations / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D020961:Lewy Body Disease / Q000150:complications / Q000523:psychology*; D009434:Neural Pathways / Q000503:physiopathology; D010300:Parkinson Disease / Q000150:complications / Q000523:psychology*; D011569:Psychiatric Status Rating Scales; D012893:Sleep Wake Disorders / Q000150:complications / Q000523:psychology