title: Do deficits in the magnocellular priming underlie visual derealization phenomena? Preliminary neurophysiological and self-report results in first-episode schizophrenia patients.
abstract: BACKGROUND
  Early visual impairments probably partially caused by impaired interactions between magnocellular (M) and parvocellular (P) pathways (M priming deficit), and disturbances of basic self-awareness or self-disorders (SDs) are core features of schizophrenia. The relationships between these features have not yet been studied. We hypothesized that the M priming was impaired in first-episode patients and that this deficit was associated with visual aspects of SDs.
  
  
  OBJECTIVE
  To investigate early visual processing in a sample of first-episode schizophrenia patients and to explore the relationships between M and P functioning and visual aspects of SDs addressed by the Examination of Anomalous Self-Experience (EASE) interview.
  
  
  METHODS
  Nine stimulating conditions were used to investigate M and P pathways and their interaction in a pattern reversal visually evoked potential (VEP) paradigm. N80 at mixed M- and P-conditions was used to investigate magnocellular priming. Generators were analyzed using source localization (Brain Electrical Source Analysis software: BESA). VEPs of nineteen first-episode schizophrenia patients were compared to those of twenty matched healthy controls by a bootstrap resample procedure. Visual aspects of SDs were analyzed through a factor analysis to separate symptom clusters of derealization phenomena. Thereafter, the associations between the main factors and the N80 component were explored using linear mixed models.
  
  
  RESULTS
  Factor analyses separated two EASE factors ("distance to the world", and "intrusive world"). The N80 component was represented by a single dipole located in the occipital visual cortex. The bootstrap analysis yielded significant amplitude reductions and prolonged latencies in first-episode patients relative to controls in response to mixed M-P conditions, and normal amplitudes and latencies in response to isolated P- and M-biased stimulation. Exploratory analyses showed significant negative correlations between the N80 amplitude values at mixed M-P conditions and the EASE factor "distance to the world", i.e. relatively higher amplitudes in the patient group were associated with higher subjective perceived derealization ("distance to the world").
  
  
  CONCLUSIONS
  The early VEP component N80 evoked by mixed M-P conditions is assumed to be a correlate of M priming, and showed reduced amplitudes and longer latencies in first-episode patients. It probably reflects a hypoactivation of the M-pathway. The negative association between visual SDs (derealization phenomena characterized by visual experiences of being more distant to the world), and the M priming deficit was counterintuitive. It might indicate a dysregulated activity of the M-pathway in patients with SDs. Further research is needed to better understand this preliminary finding.
authors.affiliation: Faculty of Psychology, University de Talca, Chile; Psychiatry Department, Centre for Psychosocial Medicine, University of Heidelberg, Voßstr. 4, 69115 Heidelberg, Germany. Electronic address: dnunez@utalca.cl.
authors.forename: D
authors.initials: D
authors.lastname: Núñez
authors.affiliation: Psychiatry Department, Centre for Psychosocial Medicine, University of Heidelberg, Voßstr. 4, 69115 Heidelberg, Germany; Department of Child and Adolescent Psychiatry, University of Heidelberg, Blumenstraße 8, 69115 Heidelberg, Germany. Electronic address: Rieke.Oelkers@med.uni-heidelberg.de.
authors.forename: R
authors.initials: R
authors.lastname: Oelkers-Ax
authors.affiliation: Psychiatry Department, Centre for Psychosocial Medicine, University of Heidelberg, Voßstr. 4, 69115 Heidelberg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: de Haan
authors.affiliation: Psychiatry Department, Centre for Psychosocial Medicine, University of Heidelberg, Voßstr. 4, 69115 Heidelberg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Ludwig
authors.affiliation: Department of Psychosomatic Medicine and Psychotherapy, Klinikum rechts der Isar, Technische Universitaet Muenchen, Langerstraße 3, 81675 Munich, Germany. Electronic address: h.sattel@tum.de.
authors.forename: H
authors.initials: H
authors.lastname: Sattel
authors.affiliation: Department of Child and Adolescent Psychiatry, University of Heidelberg, Blumenstraße 8, 69115 Heidelberg, Germany. Electronic address: Franz.Resch@med.uni-heidelberg.de.
authors.forename: F
authors.initials: F
authors.lastname: Resch
authors.affiliation: Psychiatry Department, Centre for Psychosocial Medicine, University of Heidelberg, Voßstr. 4, 69115 Heidelberg, Germany; Klinikum Karlsbad-Langensteinbach, Guttmannstrasse 1, 76307 Karlsbad, Germany. Electronic address: Matthias.Weisbrod@kkl.srh.de.
authors.forename: M
authors.initials: M
authors.lastname: Weisbrod
authors.affiliation: Psychiatry Department, Centre for Psychosocial Medicine, University of Heidelberg, Voßstr. 4, 69115 Heidelberg, Germany. Electronic address: thomas.fuchs@urz.uni-heidelberg.de.
authors.forename: T
authors.initials: T
authors.lastname: Fuchs
mesh_terms: D000293:Adolescent; D000328:Adult; D003861:Depersonalization / Q000209:etiology / Q000503:physiopathology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005829:Geniculate Bodies / Q000503:physiopathology*; D006801:Humans; D008297:Male; D060865:Repetition Priming / Q000502:physiology; D012559:Schizophrenia / Q000150:complications / Q000503:physiopathology*; D057566:Self Report; D014795:Visual Pathways / Q000503:physiopathology*; D055815:Young Adult
keywords: First-episode schizophrenia; Magnocellular priming; N80 component; Self-disorders; Visual derealization phenomena; Visual evoked potentials