Aberrant default network activations during verbal thought generation may contribute to hallucinations in schizophrenia

Abstract

International audienceSchizophrenia, particularly hallucinations, has been associated with impairments in source monitoring, whereby hallucinating patients tend to misattribute the source of a speech event to an external agent. Previous research proposed that abnormalities in generating thoughts may induce more vivid auditory sensations, which could account for misattribution from an internal to external source, possibly leading to auditory verbal hallucinations. In the present study, we investigated the neural underpinnings of a verbal thought generation (VTG) task using fMRI in 12 healthy controls and in 5 schizophrenia patients (DSM-IV). Two conditions were examined. In the first condition, participants were required to mentally generate a definition of a frequent word presented on the screen. In the second condition, participants were required to listen to the definition of a frequent word presented on the screen. An event-related fMRI protocol was used over 2 sessions of 8 minutes each. Analysis using constrained principal component analysis with a finite impulse response (FIR) model indicated that, during the mental generation task, default network regions including bilateral posterior cingulate cortex (BA 30-31), medial frontal gyrus bilaterally (BA10) and left precuneus (BA 7-19) showed less complete deactivation in schizophrenia patients relative to healthy controls. No group differences were found in task-positive networks, or the listening only condition. These results suggest abnormalities in the default network associated with the generation of thoughts, which may play a part in the genesis of auditory verbal hallucinations