title: Steady state visual evoked potential abnormalities in schizophrenia.
abstract: OBJECTIVE
  The steady state visual evoked potential (SSVEP) can be used to test the frequency response function of neural circuits. Previous studies have shown reduced SSVEPs to alpha and lower frequencies of stimulation in schizophrenia. We investigated SSVEPs in schizophrenia at frequencies spanning the theta (4Hz) to gamma (40Hz) range.
  
  
  METHODS
  The SSVEPs to seven different frequencies of stimulation (4, 8, 17, 20, 23, 30 and 40Hz) were obtained from 18 schizophrenia subjects and 33 healthy control subjects. Power at stimulating frequency (signal power) and power at frequencies above and below the stimulating frequency (noise power) were used to quantify the SSVEP responses.
  
  
  RESULTS
  Both groups showed an inverse relationship between power and frequency of stimulation. Schizophrenia subjects showed reduced signal power compared to healthy control subjects at higher frequencies (above 17Hz), but not at 4 and 8Hz at occipital region. Noise power was higher in schizophrenia subjects at frequencies between 4 and 20Hz over occipital region and at 4, 17 and 20Hz over frontal region.
  
  
  CONCLUSIONS
  SSVEP signal power at beta and gamma frequencies of stimulation were reduced in schizophrenia. Schizophrenia subjects showed higher levels of EEG noise during photic stimulation at beta and lower frequencies.
  
  
  CONCLUSIONS
  Inability to generate or maintain oscillations in neural networks may contribute to deficits in visual processing in schizophrenia.
authors.affiliation: Department of Psychology, Indiana University, 1101 E 10th Street, Bloomington, IN 47405, USA.
authors.forename: Giri P
authors.initials: GP
authors.lastname: Krishnan
authors.forename: Jenifer L
authors.initials: JL
authors.lastname: Vohs
authors.forename: William P
authors.initials: WP
authors.lastname: Hetrick
authors.forename: Christine A
authors.initials: CA
authors.lastname: Carroll
authors.forename: Anantha
authors.initials: A
authors.lastname: Shekhar
authors.forename: Marcia A
authors.initials: MA
authors.lastname: Bockbrader
authors.forename: Brian F
authors.initials: BF
authors.lastname: O'Donnell
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D004307:Dose-Response Relationship, Radiation; D004569:Electroencephalography / Q000379:methods; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005163:Factor Analysis, Statistical; D005260:Female; D006212:Hallucinations / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D012559:Schizophrenia / Q000503:physiopathology*; D013057:Spectrum Analysis; D013223:Statistics as Topic