Oscillatory TMS-EEG-Responses as a Measure of the Cortical Excitability Threshold

Jukka Saari, Elisa Kallioniemi, Mika Tarvainen, Petro Julkunen

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25 Scopus citations


Transcranial magnetic stimulation (TMS) is a non-invasive tool to perturb brain activity. In TMS studies, the stimulation intensity (SI) is commonly normalized to the resting motor threshold (rMT) that produces muscle responses in 50% of stimulations applied to the motor cortex (M1). Since rMT is influenced by spinal excitability and coil-to-cortex distance, responses recorded from the cortex, instead of a peripheral muscle, could provide a more accurate marker for cortical excitability. Combining TMS with electroencephalography (EEG) enables the measurement of brain-wide cortical reactivity to TMS. We quantified TMS-induced changes in oscillatory power and the phase of EEG with event-related spectral perturbation (ERSP) and inter-trial coherence (ITC). We studied the SI-dependency of ERSP and ITC responses by stimulating the dominant M1 of ten healthy volunteers using single-pulse TMS with 150 pulses at 60%, 80%, 100%, and 120% of rMT. We found SI-dependent ERSP and ITC responses in M1, most notably with the wide-band (8-70 Hz) early ITC responses averaged 20-60 ms after TMS. With approximately linear SI-dependence, the early ITC response was consistent between SIs (intraclass correlation = 0.78, p<0.001). Our results reveal the potential of oscillatory EEG responses, in place of rMT, as a measure of the cortical excitability threshold in M1.

Original languageEnglish (US)
Article number8125707
Pages (from-to)383-391
Number of pages9
JournalIEEE Transactions on Neural Systems and Rehabilitation Engineering
Issue number2
StatePublished - Feb 2018
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Rehabilitation
  • General Neuroscience
  • Internal Medicine
  • Biomedical Engineering


  • Cortical excitability
  • electroencephalography (EEG)
  • event-related spectral perturbation (ERSP)
  • inter-trial coherence (ITC)
  • transcranial magnetic stimulation (TMS)


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