The Neurodynamic Organization of Modality-Dependent Hallucinations
Renaud Jardri, Pierre Thomas, Christine Delmaire, Pierre Delion, Delphine Pins
Cerebral Cortex April 24, 2012 DOI: 10.1093/cercor/bhs082
Summary
A compelling finding in Neuroscience and Psychology reveals that hallucinations, including visual and auditory forms, involve a disengagement of the Default mode network (DMN). Using functional magnetic resonance imaging (fMRI) and resting state fMRI on 20 adolescents with psychosis and 20 controls, brain activity patterns showed DMN withdrawal during hallucinations mirrors responses to external stimuli. This suggests a novel pathophysiology: hallucinations arise from spontaneous DMN disengagement. The severity of these experiences, across various sensory systems and stimulus modalities, correlated with DMN instability, even persisting when symptom-free.
Abstract
The pathophysiology of hallucinations remains mysterious. This research aims to specifically explore the interaction between hallucinations and spontaneous resting-state activity. We used multimodal magnetic resonance imaging during hallucinations occurrence in 20 drug-free adolescents with a "brief psychotic disorder." They were furthermore compared with 20 matched controls at rest or during exteroceptive stimuli. Anatomical and functional symptom-mapping demonstrated reduced cortical thickness and increased blood oxygen level-dependent signal in modality-dependent association sensory cortices during auditory, visual, and multisensory hallucinations. On the contrary, primary-sensory-cortex recruitment was not systematic and was shown to be associated with increased vividness of the hallucinatory experiences. Spatiotemporal activity patterns in the default-mode network (DMN) during hallucinations and symptom-free periods in patients were compared with patterns measured in healthy individuals. A disengagement of the DMN was concomitant to hallucinations, as for exogenous stimulations in healthy participants. Specifically, spatial and temporal instabilities of the DMN correlated with the severity of hallucinations but persisted during symptom-free periods. These results suggest that hallucinatory experiences emerge from a spontaneous DMN withdrawal, providing a convincing model for hallucinations beyond the auditory modality.