title: Increased absolute magnitude of gamma synchrony in first-episode psychosis.
abstract: OBJECTIVE
  Recent studies have explored a model of the disconnection hypothesis of schizophrenia through the demonstration of abnormal stimulus induced gamma phase synchrony (GPS). These studies have principally examined synchrony in the 40 Hz band elicited in post-stimulus time periods, relative to a pre-stimulus baseline. In this study we examined the absolute magnitude of GPS elicited by a selective attention task, in first-episode psychosis (FEP). We hypothesized that FEP would be associated with abnormalities in absolute GPS, particularly when required to selectively attend to task-relevant stimuli.
  
  
  METHODS
  Fifty-five first-episode psychosis (FEP) subjects and one hundred and ten matched healthy control subjects underwent an auditory oddball selective attention task during EEG recording. The absolute magnitude of GPS was extracted for the range 35-45 Hz, and time-locked to stimulus onset. GPS averaged were computed for oddball 'target' (task-relevant) and 'non-target' (task-irrelevant) stimuli, for each subject.
  
  
  RESULTS
  FEP subjects showed a significant elevation in absolute GPS relative to controls, apparent across the 35-45 Hz range. This elevation was most marked in the left centro-temporal region, across the 800 ms post-stimulus period. In FEP subjects, the elevation in GPS was also greater for target compared to non-target stimuli, while healthy controls did not show a stimulus effect.
  
  
  CONCLUSIONS
  These findings complement previous evidence for reductions in peak gamma synchrony, calculated relative to a pre-stimulus baseline, in schizophrenia. The results an excess of absolute GPS in schizophrenia may contribute to an inability to effectively integrate task-relevant information, which underlie psychotic symptoms.
authors.affiliation: The Early Psychosis Intervention Program, Liverpool Hospital, and The Brain Dynamics Centre, Westmead Millennium Institute and Western Clinical School, University of Sydney, NSW, 2145, Australia. gary.flynn@swsahs.nsw.gov.au
authors.forename: Gary
authors.initials: G
authors.lastname: Flynn
authors.forename: David
authors.initials: D
authors.lastname: Alexander
authors.forename: Anthony
authors.initials: A
authors.lastname: Harris
authors.forename: Thomas
authors.initials: T
authors.lastname: Whitford
authors.forename: Wilson
authors.initials: W
authors.lastname: Wong
authors.forename: Cherrie
authors.initials: C
authors.lastname: Galletly
authors.forename: Steve
authors.initials: S
authors.lastname: Silverstein
authors.forename: Evian
authors.initials: E
authors.lastname: Gordon
authors.forename: Leanne M
authors.initials: LM
authors.lastname: Williams
mesh_terms: D001288:Attention / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology*; D003344:Cortical Synchronization / Q000706:statistics & numerical data*; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data*; D018913:Event-Related Potentials, P300 / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012559:Schizophrenia / Q000175:diagnosis* / Q000503:physiopathology*; D012565:Schizophrenic Psychology; D013647:Task Performance and Analysis