Hallucinations in psychosis may arise when the brain's default-mode network (DMN) disengages abnormally, similar to its response to real external stimuli. In 20 drug-free adolescents with brief psychotic disorder, multimodal MRI showed that during auditory, visual, and multisensory hallucinations, cortical thickness was reduced and blood oxygen level-dependent signal increased in modality-dependent association sensory cortices, while primary sensory cortex recruitment was not systematic and linked to greater vividness. DMN disengagement coincided with hallucinations, and spatial and temporal instabilities of the DMN correlated with hallucination severity and persisted even without symptoms. This suggests hallucinations emerge from spontaneous DMN withdrawal, offering a model beyond the auditory modality.
People with schizophrenia have a higher visual detection threshold than healthy controls, meaning they need stronger visual input to become consciously aware of it. Brain imaging showed that during conscious vision, patients failed to activate occipital areas as strongly as controls; during unconscious vision, they failed to activate a widespread network; and during the moment of becoming conscious of a visual stimulus, they failed to activate the anterior cingulate cortex.