AUDITORY HALLUCINATIONS INHIBIT EXOGENOUS ACTIVATION OF AUDITORY ASSOCIATION CORTEX

PERCEPTS unaccompanied by a veridical stimulus, such as hallucinations , provide an opportunity for mapping the neural correlates of consciou s perception. Functional magnetic resonance imaging (fMRI) can reveal localized changes in blood oxygenation in response to actual as well a s imagined sensory stimulation. The safe repeatability of fMRI enabled us to study a patient with schizophrenia while he was experiencing au ditory hallucinations and when hallucination-free (with supporting dat a from a second case). Cortical activation was measured in response to periodic exogenous auditory and visual stimulations using time series regression analysis. Functional brain images were obtained in each ha llucination condition both while the patient was on and off antipsycho tic drugs. The response of the temporal cortex to exogenous auditory s timulation (speech) was markedly reduced when the patient was experien cing hallucinating voices addressing him, regardless of medication. Vi sual cortical activation (to flashing lights) remained normal over fou r scans. From the results of this study and previous work on visual ha llucinations we conclude that hallucinations coincide with maximal act ivation of the sensory and association cortex, specific to the modalit y of the experience.