Christian Stephan-Otto1, Sara Siddi2, Carl Senior3, Jorge Cuevas-Esteban4, Maria Rosa Cambra-Martí4, Susana Ochoa1, Gildas Brébion5. 1. Institut de Recerca Sant Joan de Déu, Esplugues de Llobregat, Spain; Parc Sanitari Sant Joan de Déu, Sant Boi de Llobregat, Spain; Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Madrid, Spain. 2. Institut de Recerca Sant Joan de Déu, Esplugues de Llobregat, Spain; Parc Sanitari Sant Joan de Déu, Sant Boi de Llobregat, Spain; Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Madrid, Spain; Section of Clinical Psychology, Department of Education, Psychology, and Philosophy, University of Cagliari, Italy; Facultat de Medicina, Universitat de Barcelona, Spain. 3. School of Life & Health Sciences, Aston University, Birmingham, UK. 4. Institut de Recerca Sant Joan de Déu, Esplugues de Llobregat, Spain; Parc Sanitari Sant Joan de Déu, Sant Boi de Llobregat, Spain. 5. Institut de Recerca Sant Joan de Déu, Esplugues de Llobregat, Spain; Parc Sanitari Sant Joan de Déu, Sant Boi de Llobregat, Spain; Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Madrid, Spain. Electronic address: gildas.brebion@pssjd.org.
Abstract
BACKGROUND: Previous research suggests that visual hallucinations in schizophrenia consist of mental images mistaken for percepts due to failure of the reality-monitoring processes. However, the neural substrates that underpin such dysfunction are currently unknown. We conducted a brain imaging study to investigate the role of visual mental imagery in visual hallucinations. METHOD: Twenty-three patients with schizophrenia and 26 healthy participants were administered a reality-monitoring task whilst undergoing an fMRI protocol. At the encoding phase, a mixture of pictures of common items and labels designating common items were presented. On the memory test, participants were requested to remember whether a picture of the item had been presented or merely its label. RESULTS: Visual hallucination scores were associated with a liberal response bias reflecting propensity to erroneously remember pictures of the items that had in fact been presented as words. At encoding, patients with visual hallucinations differentially activated the right fusiform gyrus when processing the words they later remembered as pictures, which suggests the formation of visual mental images. On the memory test, the whole patient group activated the anterior cingulate and medial superior frontal gyrus when falsely remembering pictures. However, no differential activation was observed in patients with visual hallucinations, whereas in the healthy sample, the production of visual mental images at encoding led to greater activation of a fronto-parietal decisional network on the memory test. CONCLUSIONS: Visual hallucinations are associated with enhanced visual imagery and possibly with a failure of the reality-monitoring processes that enable discrimination between imagined and perceived events.
BACKGROUND: Previous research suggests that visual hallucinations in schizophrenia consist of mental images mistaken for percepts due to failure of the reality-monitoring processes. However, the neural substrates that underpin such dysfunction are currently unknown. We conducted a brain imaging study to investigate the role of visual mental imagery in visual hallucinations. METHOD: Twenty-three patients with schizophrenia and 26 healthy participants were administered a reality-monitoring task whilst undergoing an fMRI protocol. At the encoding phase, a mixture of pictures of common items and labels designating common items were presented. On the memory test, participants were requested to remember whether a picture of the item had been presented or merely its label. RESULTS:Visual hallucination scores were associated with a liberal response bias reflecting propensity to erroneously remember pictures of the items that had in fact been presented as words. At encoding, patients with visual hallucinations differentially activated the right fusiform gyrus when processing the words they later remembered as pictures, which suggests the formation of visual mental images. On the memory test, the whole patient group activated the anterior cingulate and medial superior frontal gyrus when falsely remembering pictures. However, no differential activation was observed in patients with visual hallucinations, whereas in the healthy sample, the production of visual mental images at encoding led to greater activation of a fronto-parietal decisional network on the memory test. CONCLUSIONS:Visual hallucinations are associated with enhanced visual imagery and possibly with a failure of the reality-monitoring processes that enable discrimination between imagined and perceived events.