Our perceived reality is not an objective reality. Instead, our experience of the world is a compromise between the signals that reach the brain and what our brain expects. Expectations can therefore affect how our minds process both the present and the future. The evolutionary benefit to predict the future is that the organism can behave in a pro-active manner. The advantage to use expectations in analysing the present is that our brain can better model and understand the surrounding world. We hypothesis that integrating expectations with the present also leads to such phenomena as the placebo effect. In that case the wide spectrum of robust placebo effects that are observed in pain, depression and Parkinson’s disease have the same underlying cause. Moreover, we suggest that similar processes are involved in other distortions of reality such as in psychotic delusions.

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From prediction error to psychosis: ketamine as a pharmacological model of delusions. <http://www.ncbi.nlm.nih.gov/pubmed/17591652?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum>  Corlett PR, Honey GD, Fletcher PC. J Psychopharmacol. 2007 May;21(3):238-52. Review.

to placebo programme