title: Gamma-band auditory steady-state responses are impaired in first episode psychosis.
abstract: BACKGROUND
  In chronic schizophrenia and chronic bipolar disorder, gamma band (30-100 Hz) auditory steady-state electroencephalogram responses (ASSRs) are reduced in power and phase locking, likely reflecting neural circuit dysfunction. Here we examined whether gamma ASSR deficits are also present at first hospitalization for psychosis.
  
  
  METHODS
  Subjects were 16 first episode schizophrenia patients (SZ), 16 first episode affective disorder patients (AFF) (13 with bipolar disorder), and 33 healthy control subjects (HC). Stimuli were 20-, 30-, and 40-Hz binaural click trains. The ASSR phase locking and evoked power were analyzed with the Morlet wavelet transform.
  
  
  RESULTS
  At 40-Hz stimulation, SZ and AFF had significantly reduced phase locking compared with HC. This deficit was more pronounced over the left hemisphere in SZ. Evoked power at 40 Hz was also reduced in the patients compared with HC. At 30-Hz stimulation phase locking and evoked power were reduced in both patient groups. The 20-Hz ASSR did not differ between groups, but phase locking and evoked power of the 40-Hz harmonic of the 20-Hz ASSR were reduced in both SZ and AFF. Phase locking of this 40-Hz harmonic was correlated with total positive symptoms in SZ.
  
  
  CONCLUSIONS
  The gamma ASSR deficit is present at first hospitalization for both schizophrenia and affective disorder but shows a left hemisphere bias in first hospitalized SZ. Some of the neural circuitry abnormalities underlying the gamma ASSR deficit might be common to psychoses in general, whereas others might be specific to particular disorders.
authors.affiliation: Department of Psychiatry, VA Boston Healthcare System and Harvard Medical School, Brockton 02301, USA. kevin_spencer@hms.harvard.edu
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Spencer
authors.forename: Dean F
authors.initials: DF
authors.lastname: Salisbury
authors.forename: Martha E
authors.initials: ME
authors.lastname: Shenton
authors.forename: Robert W
authors.initials: RW
authors.lastname: McCarley
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D001307:Auditory Perception / Q000502:physiology; D004569:Electroencephalography / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011601:Psychophysics; D011618:Psychotic Disorders / Q000503:physiopathology*