Danilo R de Jesus1, Gabriela Pereira de Souza Favalli1, Sylco S Hoppenbrouwers2, Mera S Barr1, Robert Chen3, Paul B Fitzgerald4, Zafiris J Daskalakis5. 1. Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada. 2. Department of Psychology, Utrecht University, Utrecht, The Netherlands. 3. Department of Medicine, University of Toronto, Toronto, Ontario, Canada. 4. Monash Alfred Psychiatry Research Centre, The Alfred and Monash University Central Clinical School, Commercial Rd, Melbourne, Victoria, Australia. 5. Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario, Canada. Electronic address: Jeff.Daskalakis@camh.ca.
Abstract
OBJECTIVES: 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. CONCLUSION: Only high frequency rTMS potentiated CI. Longer treatment durations are required to produce such changes. SIGNIFICANCE: 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.
OBJECTIVES: 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. CONCLUSION: Only high frequency rTMS potentiated CI. Longer treatment durations are required to produce such changes. SIGNIFICANCE: 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.
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