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The computational anatomy of psychosis.

Adams, RA; Stephan, KE; Brown, HR; Frith, CD; Friston, KJ; (2013) The computational anatomy of psychosis. Front Psychiatry , 4 (47) 10.3389/fpsyt.2013.00047. Green open access

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Abstract

This paper considers psychotic symptoms in terms of false inferences or beliefs. It is based on the notion that the brain is an inference machine that actively constructs hypotheses to explain or predict its sensations. This perspective provides a normative (Bayes-optimal) account of action and perception that emphasizes probabilistic representations; in particular, the confidence or precision of beliefs about the world. We will consider hallucinosis, abnormal eye movements, sensory attenuation deficits, catatonia, and delusions as various expressions of the same core pathology: namely, an aberrant encoding of precision. From a cognitive perspective, this represents a pernicious failure of metacognition (beliefs about beliefs) that can confound perceptual inference. In the embodied setting of active (Bayesian) inference, it can lead to behaviors that are paradoxically more accurate than Bayes-optimal behavior. Crucially, this normative account is accompanied by a neuronally plausible process theory based upon hierarchical predictive coding. In predictive coding, precision is thought to be encoded by the post-synaptic gain of neurons reporting prediction error. This suggests that both pervasive trait abnormalities and florid failures of inference in the psychotic state can be linked to factors controlling post-synaptic gain - such as NMDA receptor function and (dopaminergic) neuromodulation. We illustrate these points using biologically plausible simulations of perceptual synthesis, smooth pursuit eye movements and attribution of agency - that all use the same predictive coding scheme and pathology: namely, a reduction in the precision of prior beliefs, relative to sensory evidence.

Type: Article
Title: The computational anatomy of psychosis.
Location: Switzerland
Open access status: An open access version is available from UCL Discovery
DOI: 10.3389/fpsyt.2013.00047
Publisher version: http://dx.doi.org/10.3389/fpsyt.2013.00047
Language: English
Additional information: This work is licensed under the Creative Commons Attribution License, Attribution 3.0 Unported (CC BY 3.0) http://creativecommons.org/licenses/by/3.0/ which permits unrestricted use, distribution, and reproduction in any medium. However, you must attribute the work to the author (but not in any way that suggests that they endorse you or your use of the work). PMCID: PMC3667557
Keywords: active inference, free energy, illusions, precision, psychosis, schizophrenia, sensory attenuation
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Imaging Neuroscience
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Computer Science
URI: https://discovery.ucl.ac.uk/id/eprint/1396466
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