From hallucinations to synaesthesia: A circular inference account of unimodal and multimodal erroneous percepts in clinical and drug-induced psychosis.

Pantelis Leptourgos; Vincent Bouttier; Sophie Denève; Renaud Jardri

doi:10.1016/j.neubiorev.2022.104593

From hallucinations to synaesthesia: A circular inference account of unimodal and multimodal erroneous percepts in clinical and drug-induced psychosis.

Pantelis Leptourgos, Vincent Bouttier, Sophie Denève, Renaud Jardri

Neuroscience and biobehavioral reviews April 2022 DOI: 10.1016/j.neubiorev.2022.104593 (opens in new tab)

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Characteristics	Theoretical or philosophical paper Peer reviewed
Topics	Ayahuasca DMT
Keywords	Bayes Circular inference Hallucinations Microcircuit Multimodal Psychedelics Schizophrenia Synaesthesia Unimodal
Key points	Argues that erroneous percepts can be unified under a "circular inference" account: amplified top-down predictions produce excessive reliance on priors and crossmodal percepts and stronger illusions, while amplified bottom-up information produces overinterpretation of unreliable sensory input, unimodal hallucinations, and reduced vulnerability to illusions. Proposes a canonical microcircuit in which layer-specific inhibition controls propagation across hierarchical levels, with deep-layer interneurons controlling priors and supragranular inhibition counterbalancing ascending loops.

Abstract

Psychedelics distort perception and induce visual and multimodal hallucinations as well as synaesthesia. This is in contradiction with the high prevalence of distressing voices in schizophrenia. Here we introduce a unifying account of unimodal and multimodal erroneous percepts based on circular inference. We show that amplification of top-down predictions (descending loops) leads to an excessive reliance on priors and aberrant levels of integration of the sensory representations, resulting in crossmodal percepts and stronger illusions. By contrast, amplification of bottom-up information (ascending loops) results in overinterpretation of unreliable sensory inputs and high levels of segregation between sensory modalities, bringing about unimodal hallucinations and reduced vulnerability to illusions. We delineate a canonical microcircuit in which layer-specific inhibition controls the propagation of information across hierarchical levels: inhibitory interneurons in the deep layers exert control over priors, removing descending loops. Conversely, inhibition in the supragranular layers counterbalances the effects of the ascending loops. Overall, we put forward a multiscale and transnosographic account of erroneous percepts with important theoretical, conceptual and clinical implications.

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