title: Ketamine-Induced Hallucinations.
abstract: BACKGROUND
  Ketamine, the NMDA glutamate receptor antagonist drug, is increasingly employed as an experimental model of psychosis in healthy volunteers. At subanesthetic doses, it safely and reversibly causes delusion-like ideas, amotivation and perceptual disruptions reminiscent of the aberrant salience experiences that characterize first-episode psychosis. However, auditory verbal hallucinations, a hallmark symptom of schizophrenia, have not been reported consistently in healthy volunteers even at high doses of ketamine.
  
  
  METHODS
  Here we present data from a set of healthy participants who received moderately dosed, placebo-controlled ketamine infusions in the reduced stimulation environment of the magnetic resonance imaging (MRI) scanner. We highlight the phenomenological experiences of 3 participants who experienced particularly vivid hallucinations.
  
  
  RESULTS
  Participants in this series reported auditory verbal and musical hallucinations at a ketamine dose that does not induce auditory hallucination outside of the scanner.
  
  
  CONCLUSIONS
  We interpret the observation of ketamine-induced auditory verbal hallucinations in the context of the reduced perceptual environment of the MRI scanner and offer an explanation grounded in predictive coding models of perception and psychosis - the brain fills in expected perceptual inputs, and it does so more in situations of altered perceptual input. The altered perceptual input of the MRI scanner creates a mismatch between top-down perceptual expectations and the heightened bottom-up signals induced by ketamine. Such circumstances induce aberrant percepts, including musical and auditory verbal hallucinations. We suggest that these circumstances might represent a useful experimental model of auditory verbal hallucinations and highlight the impact of ambient sensory stimuli on psychopathology.
authors.affiliation: Department of Psychiatry, Yale School of Medicine, Yale University, New Haven, Conn., USA.
authors.forename: Albert R
authors.initials: AR
authors.lastname: Powers
authors.forename: Mark G
authors.initials: MG
authors.lastname: Gancsos
authors.forename: Emily S
authors.initials: ES
authors.lastname: Finn
authors.forename: Peter T
authors.initials: PT
authors.lastname: Morgan
authors.forename: Philip R
authors.initials: PR
authors.lastname: Corlett
mesh_terms: D000328:Adult; D003702:Delusions / Q000139:chemically induced; D004305:Dose-Response Relationship, Drug; D005260:Female; D005625:Frontal Lobe / Q000187:drug effects* / Q000503:physiopathology*; D006212:Hallucinations / Q000139:chemically induced* / Q000175:diagnosis; D006801:Humans; D007649:Ketamine / Q000008:administration & dosage / Q000009:adverse effects*; D008279:Magnetic Resonance Imaging; D008297:Male; D010465:Perception; D011618:Psychotic Disorders / Q000188:drug therapy* / Q000473:pathology; D055815:Young Adult
chemical_list: D007649:Ketamine