title: Determining optimal rTMS parameters through changes in cortical inhibition.
abstract: OBJECTIVE
  Evidence shows that repetitive transcranial magnetic stimulation (rTMS) changes cortical inhibition (CI) and excitability and that these changes may relate to its therapeutic effects. This study aimed to investigate the effects of differing durations or 'doses' of rTMS on cortical inhibition and excitability in healthy subjects.
  
  
  METHODS
  Four different experiments were conducted: 1 session of 1200 pulses of 1 or 20 Hz active or sham rTMS; 10 sessions of 1 or 20 Hz active or sham rTMS, 1200 pulses/session; 1 session of 3600 pulses of 1 or 20 Hz active or sham rTMS; 1 session of 6000 pulses of 20 Hz active or sham rTMS. Measures of cortical inhibition and excitability included short-interval intracortical inhibition, long interval cortical inhibition, cortical silent period (CSP), motor evoked potential amplitude, resting motor threshold and intracortical facilitation.
  
  
  RESULTS
  Only 6000 pulses of 20 Hz rTMS lead to a significant lengthening of the CSP and therefore potentiation of CI. There were no changes to excitability measures.
  
  
  CONCLUSIONS
  Only high frequency rTMS potentiated CI. Longer treatment durations are required to produce such changes.
  
  
  CONCLUSIONS
  Studies investigating the therapeutic effects of rTMS may benefit from extended dosing with increased number of pulses per session. CSP lengthening may be used to guide treatment response.
authors.affiliation: Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Danilo R
authors.initials: DR
authors.lastname: de Jesus
authors.affiliation: Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Gabriela Pereira de Souza
authors.initials: GPS
authors.lastname: Favalli
authors.affiliation: Department of Psychology, Utrecht University, Utrecht, The Netherlands.
authors.forename: Sylco S
authors.initials: SS
authors.lastname: Hoppenbrouwers
authors.affiliation: Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Mera S
authors.initials: MS
authors.lastname: Barr
authors.affiliation: Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
authors.affiliation: Monash Alfred Psychiatry Research Centre, The Alfred and Monash University Central Clinical School, Commercial Rd, Melbourne, Victoria, Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fitzgerald
authors.affiliation: Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada. Electronic address: Jeff.Daskalakis@camh.ca.
authors.forename: Zafiris J
authors.initials: ZJ
authors.lastname: Daskalakis
mesh_terms: D000293:Adolescent; D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Cortical excitability; Cortical inhibition; GABA; Motor cortex; Repetitive transcranial magnetic stimulation