N-methyl-d-aspartate receptor hypofunction causes recurrent and transient failures of perceptual inference

Perception integrates external sensory signals with internal predictions that reflect prior knowledge about the world. Previous research suggests that this integration is governed by slow alternations between an external mode, driven by sensory signals, and an internal mode, shaped by prior knowledge.Using a double-blind, placebo-controlled, cross-over experiment in healthy human participants, we investigated the effects of the N-methyl-D-aspartate receptor (NMDAR) antagonist S-ketamine on the balance between external and internal modes.We found that S-ketamine causes a shift of perception towards the external mode. A case-control study revealed that individuals with paranoid schizophrenia, a disorder repeatedly associated with NMDAR hypofunction, spend more time in the external mode. This NMDAR-dependent increase in the external mode suggests that the symptoms of schizophrenia are caused by recurring dissociations of perception from prior knowledge about the world. Perception combines external sensory signals with internal predictions that reflect prior knowledge about the world. Weilnhammer et al. show that the NMDAR antagonist ketamine, and schizophrenia-a disorder characterized by NMDAR hypofunction-are both associated with a shift of perception towards external sensory signals.