title: The effect of repetitive transcranial magnetic stimulation on gamma oscillatory activity in schizophrenia.
abstract: BACKGROUND
  Gamma (γ) oscillations (30-50 Hz) have been shown to be excessive in patients with schizophrenia (SCZ) during working memory (WM). WM is a cognitive process that involves the online maintenance and manipulation of information that is mediated largely by the dorsolateral prefrontal cortex (DLPFC). Repetitive transcranial magnetic stimulation (rTMS) represents a non-invasive method to stimulate the cortex that has been shown to enhance cognition and γ oscillatory activity during WM.
  
  
  RESULTS
  We examined the effect of 20 Hz rTMS over the DLPFC on γ oscillatory activity elicited during the N-back task in 24 patients with SCZ compared to 22 healthy subjects. Prior to rTMS, patients with SCZ elicited excessive γ oscillatory activity compared to healthy subjects across WM load. Active rTMS resulted in the reduction of frontal γ oscillatory activity in patients with SCZ, while potentiating activity in healthy subjects in the 3-back, the most difficult condition. Further, these effects on γ oscillatory activity were found to be specific to the frontal brain region and were absent in the parieto-occipital brain region.
  
  
  CONCLUSIONS
  We suggest that this opposing effect of rTMS on γ oscillatory activity in patients with SCZ versus healthy subjects may be related to homeostatic plasticity leading to differential effects of rTMS on γ oscillatory activity depending on baseline differences. These findings provide important insights into the neurophysiological mechanisms underlying WM deficits in SCZ and demonstrated that rTMS can modulate γ oscillatory activity that may be a possible avenue for cognitive potentiation in this disorder.
authors.affiliation: Schizophrenia Program, Department of Psychiatry, Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Mera S
authors.initials: MS
authors.lastname: Barr
authors.forename: Faranak
authors.initials: F
authors.lastname: Farzan
authors.forename: Tamara
authors.initials: T
authors.lastname: Arenovich
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fitzgerald
authors.forename: Zafiris J
authors.initials: ZJ
authors.lastname: Daskalakis
mesh_terms: D000328:Adult; D014150:Antipsychotic Agents / Q000494:pharmacology / Q000627:therapeutic use; D001519:Behavior / Q000187:drug effects; D016022:Case-Control Studies; D003710:Demography; D004569:Electroencephalography; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000187:drug effects / Q000502:physiology*; D008875:Middle Aged; D009483:Neuropsychological Tests; D017397:Prefrontal Cortex / Q000187:drug effects / Q000503:physiopathology; D012559:Schizophrenia / Q000188:drug therapy / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
chemical_list: D014150:Antipsychotic Agents