Variability in neural excitability and plasticity induction in the human cortex: A brain stimulation study

Brenton Hordacre, Mitchell R. Goldsworthy, Ann Maree Vallence, Sam Darvishi, Bahar Moezzi, Masashi Hamada, John C. Rothwell, Michael C. Ridding

Research output: Contribution to journalArticlepeer-review

92 Citations (Scopus)


Background The potential of non-invasive brain stimulation (NIBS) for both probing human neuroplasticity and the induction of functionally relevant neuroplastic change has received significant interest. However, at present the utility of NIBS is limited due to high response variability. One reason for this response variability is that NIBS targets a diffuse cortical population and the net outcome to stimulation depends on the relative levels of excitability in each population. There is evidence that the relative excitability of complex oligosynaptic circuits (late I-wave circuits) as assessed by transcranial magnetic stimulation (TMS) is useful in predicting NIBS response. Objective Here we examined whether an additional marker of cortical excitability, MEP amplitude variability, could provide additional insights into response variability following application of the continuous theta burst stimulation (cTBS) NIBS protocol. Additionally we investigated whether I-wave recruitment was associated with MEP variability. Methods Thirty-four healthy subjects (15 male, aged 18–35 years) participated in two experiments. Experiment 1 investigated baseline MEP variability and cTBS response. Experiment 2 determined if I-wave recruitment was associated with MEP variability. Results Data show that both baseline MEP variability and late I-wave recruitment are associated with cTBS response, but were independent of each other; together, these variables predict 31% of the variability in cTBS response. Conclusions This study provides insight into the physiological mechanisms underpinning NIBS plasticity responses and may facilitate development of more reliable NIBS protocols.

Original languageEnglish
Pages (from-to)588-595
Number of pages8
JournalBrain Stimulation
Issue number3
Publication statusPublished or Issued - May 2017
Externally publishedYes


  • Motor cortex
  • Motor evoked potential
  • Theta burst stimulation
  • Transcranial magnetic stimulation
  • Variability

ASJC Scopus subject areas

  • Biophysics
  • Neuroscience(all)
  • Clinical Neurology

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