title: Increased visual gamma power in schizoaffective bipolar disorder.
abstract: BACKGROUND
  Electroencephalography and magnetoencephalography (MEG) studies have identified alterations in gamma-band (30-80 Hz) cortical activity in schizophrenia and mood disorders, consistent with neural models of disturbed glutamate (and GABA) neuron influence over cortical pyramidal cells. Genetic evidence suggests specific deficits in GABA-A receptor function in schizoaffective bipolar disorder (SABP), a clinical syndrome with features of both bipolar disorder and schizophrenia. This study investigated gamma oscillations in this under-researched disorder.
  
  
  METHODS
  MEG was used to measure induced gamma and evoked responses to a visual grating stimulus, known to be a potent inducer of primary visual gamma oscillations, in 15 individuals with remitted SABP, defined using Research Diagnostic Criteria, and 22 age- and sex-matched healthy controls.
  
  
  RESULTS
  Individuals with SABP demonstrated increased sustained visual cortical power in the gamma band (t 35 = -2.56, p = 0.015) compared to controls. There were no group differences in baseline gamma power, transient or sustained gamma frequency, alpha band responses or pattern onset visual-evoked responses.
  
  
  CONCLUSIONS
  Gamma power is increased in remitted SABP, which reflects an abnormality in the cortical inhibitory-excitatory balance. Although an interaction between gamma power and medication can not be ruled out, there were no group differences in evoked responses or baseline measures. Further work is needed in other clinical populations and at-risk relatives. Pharmaco-magnetoencephalography studies will help to elucidate the specific GABA and glutamate pathways affected.
authors.affiliation: Institute of Psychological Medicine and Clinical Neurosciences, MRC Centre for Neuropsychiatric Genetics and Genomics,Cardiff University School of Medicine,Hadyn Ellis Building, Cardiff,UK.
authors.forename: J A
authors.initials: JA
authors.lastname: Brealy
authors.affiliation: Institute of Psychological Medicine and Clinical Neurosciences, MRC Centre for Neuropsychiatric Genetics and Genomics,Cardiff University School of Medicine,Hadyn Ellis Building, Cardiff,UK.
authors.forename: A
authors.initials: A
authors.lastname: Shaw
authors.affiliation: Cardiff University Brain Research Imaging Centre, School of Psychology,Cardiff University,Park Place, Cardiff,UK.
authors.forename: H
authors.initials: H
authors.lastname: Richardson
authors.affiliation: Cardiff University Brain Research Imaging Centre, School of Psychology,Cardiff University,Park Place, Cardiff,UK.
authors.forename: K D
authors.initials: KD
authors.lastname: Singh
authors.affiliation: Cardiff University Brain Research Imaging Centre, School of Psychology,Cardiff University,Park Place, Cardiff,UK.
authors.forename: S D
authors.initials: SD
authors.lastname: Muthukumaraswamy
authors.affiliation: Institute of Psychological Medicine and Clinical Neurosciences, MRC Centre for Neuropsychiatric Genetics and Genomics,Cardiff University School of Medicine,Hadyn Ellis Building, Cardiff,UK.
authors.forename: P A
authors.initials: PA
authors.lastname: Keedwell
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000503:physiopathology*; D002540:Cerebral Cortex / Q000503:physiopathology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D065818:Gamma Rhythm / Q000502:physiology*; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D011618:Psychotic Disorders / Q000503:physiopathology*
keywords: visual