title: Pareidolia in Parkinson's disease without dementia: A positron emission tomography study.
abstract: BACKGROUND
  Pareidolia, 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.
  
  
  METHODS
  A 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.
  
  
  RESULTS
  PD 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.
  
  
  CONCLUSIONS
  Our 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.
authors: 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 Welfare, Niigata, Japan.
authors: Makoto
authors: M
authors: Uchiyama
authors: Department of Behavioral Neurology and Cognitive Neuroscience, Tohoku University School of Medicine, Sendai, Japan. Electronic address: nishiou@med.tohoku.ac.jp.
authors: Yoshiyuki
authors: Y
authors: Nishio
authors: Department of Behavioral Neurology and Cognitive Neuroscience, Tohoku University School of Medicine, Sendai, Japan.
authors: Kayoko
authors: K
authors: Yokoi
authors: Department of Diagnostic Image Analysis, Tohoku University School of Medicine, Sendai, Japan.
authors: Yoshiyuki
authors: Y
authors: Hosokai
authors: Department of Neurology, Sendai Nishitaga National Hospital, Sendai, Japan.
authors: Atsushi
authors: A
authors: Takeda
authors: Department of Behavioral Neurology and Cognitive Neuroscience, Tohoku University School of Medicine, Sendai, Japan.
authors: Etsuro
authors: E
authors: Mori
mesh_terms: D000368:Aged; D003704:Dementia / Q000503:physiopathology; D004734:Energy Metabolism; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism; D007839:Functional Laterality; D006212:Hallucinations / Q000503:physiopathology*; D006801:Humans; D007088:Illusions / Q000523:psychology*; D008297:Male; D008875:Middle Aged; D009778:Occipital Lobe / Q000000981:diagnostic imaging / Q000503:physiopathology; D010296:Parietal Lobe / Q000000981:diagnostic imaging / Q000503:physiopathology*; D010300:Parkinson Disease / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000523:psychology*; D010775:Photic Stimulation / Q000379:methods; D049268:Positron-Emission Tomography / Q000379:methods; D013702:Temporal Lobe / Q000000981:diagnostic imaging / Q000503:physiopathology
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: Parkinson's disease; Psychosis; Visual hallucinations; Visual illusions