title: Early and late stages of visual processing in individuals in prodromal state and first episode schizophrenia: an ERP study.
abstract: BACKGROUND
  P300 deficits in schizophrenia patients are well established, especially in the auditory modality. Several studies have also reported P300 abnormalities in schizophrenia in visual tasks, but these findings are inconsistent. Furthermore, reports on P300 in visual modality in prodromal subjects are very limited. While P300 indexes relatively late and complex cognitive functions such as context updating in working memory, sensory-evoked components such as the P1/N1 primarily index early stages of perceptual processing. Several previous studies suggest that P300 reduction in schizophrenia patients may be dissociable from these earlier components. Therefore, in this study, we measured the P300 component as well as the P1/N1 in a visual oddball paradigm in prodromal subjects and first episode schizophrenia patients, and compared them with those of healthy controls.
  
  
  METHODS
  Visual P300 and P1/N1 were obtained from prodromal (PRO, n = 23), first episode schizophrenia patients (SZ, n = 17), and healthy control subjects (HC, n = 31), who silently counted infrequent target stimuli ("X") amid standard stimuli ("Y") presented on the screen while 64-channel EEG was recorded.
  
  
  RESULTS
  Both PRO and SZ subjects showed reduced P300 amplitudes and delayed P300 peak latencies in comparison to control subjects. On the other hand, N1 amplitude was significantly reduced only in SZ but not in PRO. Increased severity of positive symptoms was significantly associated with smaller P300 amplitude in PRO.
  
  
  CONCLUSIONS
  These results suggest that visual P300 is affected already at the prodromal stage and could be a marker of the prodromal phase of schizophrenia.
authors: Clinical Neuroscience Division, Laboratory of Neuroscience, VA Boston Healthcare System-Brockton Division, Department of Psychiatry, Harvard Medical School, Brockton, MA, United States.
authors: Naoya
authors: N
authors: Oribe
authors: Yoji
authors: Y
authors: Hirano
authors: Shigenobu
authors: S
authors: Kanba
authors: Elisabetta C
authors: EC
authors: del Re
authors: Larry J
authors: LJ
authors: Seidman
authors: Raquelle
authors: R
authors: Mesholam-Gately
authors: Kevin M
authors: KM
authors: Spencer
authors: Robert W
authors: RW
authors: McCarley
authors: Margaret A
authors: MA
authors: Niznikiewicz
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D004569:Electroencephalography; D018913:Event-Related Potentials, P300 / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D062706:Prodromal Symptoms; D011569:Psychiatric Status Rating Scales; D011930:Reaction Time / Q000502:physiology; D012559:Schizophrenia / Q000503:physiopathology*; D013223:Statistics as Topic; D013997:Time Factors; D055815:Young Adult