Mapping Auditory Hallucinations in Schizophrenia Using Functional Magnetic Resonance Imaging

Abstract

AUDITORY VERBAL hallucinations (hereafter called auditory hallucinations) are perceptions of external speech in the absence of a stimulus and a cardinal feature of schizophrenia. Functional imaging provides a means of studying their pathophysiology in vivo. Previous neuroimaging studies have sought to "capture" the pattern of activity during auditory hallucinations by asking patients to signal when they occur,^1-3 but the results have been inconsistent. This may reflect the confounding effects of signaling the presence of hallucinations, which can engage areas theoretically implicated in auditory hallucinations,⁴ as well as small numbers of subjects^2,3 and the acquisition of a limited number of images per subject.¹ Most previous studies, with a few exceptions,³ involved single-photon or positron emission tomography (SPET or PET), which, while silent, constrain the number of scans that can be safely acquired. Studies may have also differed in terms of the characteristics of the patients and hallucinations that have been examined. We have developed a method that measures spontaneous neural activity using functional magnetic resonance imaging (fMRI) and permits the acquisition of a relatively large number of images in each subject, without the subject having to signal when auditory hallucinations occur. Moreover, while the scanner noise generated during conventional fMRI can itself activate auditory cortex,⁵ our approach allows activity during auditory hallucinations to be examined in silence. This "random sampling" method can be viewed as a variant of event-related fMRI⁶ that measures the neural correlates of discrete cognitive events, in this case spontaneous hallucinations, rather than the neural response to experimentally presented stimuli.