The Japanese journal of neuropsychology

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ArticleTitle	Late-life delusion: Development of concept and neurocognitive mechanisms
Language	J
AuthorList	Keisuke Takahata¹⁾²⁾, Masaru Mimura¹⁾
Affiliation	¹⁾Department of Neuropsychiatry, Keio University School of Medicine ²⁾Clinical Neuroimaging Team, Molecular Neuroimaging Program, Molecular Imaging Center, National Institute of Radiological Sciences
Publication	Japanese Journal of Neuropsychology: 29 (4), 243-256, 2013
Received
Accepted
Abstract	In this article, we reviewed empirical findings on epidemiology and psychological mechanisms of late-life delusions. Community sample studies showed that 4-10% of elderly people have delusional ideations. Although emergence of delusions in late life has been described for more than a century, this symptom poses a number of problems. First, there have been serious confusions in terminology and concepts associated with delusion in late life, which has been impediment for comparison of research findings. The central question is whether delusion in late life is a variant of schizophrenia or manifestation of different disease. We therefore first looked back the historical development of concepts of late-life delusions. Late paraphrenia is essentially a British concept of delusions that begin after age of 60. In Germany, late-onset schizophrenia was adopted to describe a form of schizophrenia in elderly. In Japan, the concept of "paranoid spectrum", has been suggested which covers paranoid reaction in normal subjects through primary delusions in schizophrenia. Despite the heterogeneity of clinical concepts, core features are considerably similar, prompting further clinical investigation. Second problem is a difficulty to distinguish delusional ideations from normal belief. Although classical psychopathology treated normal belief and delusion as completely distinct processes, recent behavioral and neurocognitive studies regard them as a continuum, and have suggested that they could be explained in a common framework. In the second section of this article, therefore, we focused on the current neurocognitive models of delusion, especially two-factors theory and Bayesian inference model. Two-factors theory, originally purposed to explain monothematic delusion such as Capgra's delusion, also provides useful framework to understand mechanisms underlying polythematic delusions in late life. Processes of belief formation can be formulated in terms of Bayesian inference model. Bayesian inference model is useful to understand both formation and maintenance of delusional beliefs. Influence of age-related changes in cognitive functions, personality, social situations, alteration of bodily sensations and impaired dopaminergic function on Bayesian inferential processes were discussed.
Keywords	late-life delusion, late paraphrenia, late-onset schizophrenia, two-factors theory, Bayesian inference