Magnetic Resonance Spectroscopy Investigation of Conditioned Auditory Percepts

The neurobiology of hallucinations is complex, and despite over a century of research it has yet to be fully characterized. The observation that auditory hallucinations occur in healthy individuals may provide new avenues for understanding its neurobiology in psychopathology. Bayesian approaches to perception suggest that aberrant experiences can be conditioned, with stronger effects in those prone to hallucinations. Through a combination of functional magnetic resonance imaging and magnetic resonance spectroscopy, the present study investigated whether differences in the endorsement of conditioned hallucinations was associated with differences in anterior cingulate cortex (ACC) glutamate and GABA levels in a healthy, college-aged sample that differed in their propensity to endorse perceptual abnormalities. Hallucinators were more likely to endorse false percepts and were more confident in their responses during a Pavlovian conditioning task that paired an auditory stimulus with a visual stimulus. Conditioned hallucinations were positively correlated with self-report scores of hallucination-proneness in daily life. Hallucinators had a higher ratio of glutamate to creatine in the ACC compared to a control region, but there were no such differences in GABA/creatine ratios. Conservatively, these results suggest that the predictive coding account of hallucinations in healthy individuals overlaps with the underlying neurobiology of psychosis in disease states, and that such an approach may be especially useful for understanding psychosis risk across development