• Makoto Uchiyama, Yoshiyuki Nishio, Kayoko Yokoi, Yoshiyuki Hosokai, Atsushi Takeda, and Etsuro Mori.
• Department of Behavioral Neurology and Cognitive Neuroscience, Tohoku University School of Medicine, Sendai, Japan; Department of Speech, Language and Hearing Sciences, Niigata University of Health and Wel... more fare, Niigata, Japan. less
• Parkinsonism Relat. Disord. 2015 Jun 1; 21 (6): 603-9.

BackgroundPareidolia, which is a particular type of complex visual illusion, has been reported to be a phenomenon analogous to visual hallucinations in patients with dementia with Lewy bodies. However, whether pareidolia is observed in Parkinson's disease (PD) or whether there are common underlying mechanisms of these two types of visual misperceptions remains to be elucidated.MethodsA test to evoke pareidolia, the Pareidolia test, was administered to 53 patients with PD without dementia and 24 healthy controls. The regional cerebral metabolic rate of glucose was measured using 18F-fluorodeoxyglucose positron emission tomography in the PD patients.ResultsPD patients without dementia produced a greater number of pareidolic illusions compared with the controls. Pareidolia was observed in all of the patients having visual hallucinations as well as a subset of those without visual hallucinations. The number of pareidolic illusions was correlated with hypometabolism in the bilateral temporal, parietal and occipital cortices. The index of visual hallucinations was correlated with hypometabolism in the left parietal cortex. A region associated with both pareidolia and visual hallucinations was found in the left parietal lobe.ConclusionsOur study suggests that PD patients without dementia experience pareidolia more frequently than healthy controls and that posterior cortical dysfunction could be a common neural mechanism of pareidolia and visual hallucinations. Pareidolia could represent subclinical hallucinations or a predisposition to visual hallucinations in Lewy body disease.Copyright © 2015 Elsevier Ltd. All rights reserved.

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