The effect of stimulation frequency on transcranial evoked potentials

Introduction: Transcranial magnetic stimulation-evoked electroencephalography potentials (TEPs) have been used to study motor cortical excitability in healthy subjects and several neurological conditions. However, optimal recording parameters for TEPs are still debated. Stimulation rates could affect TEP amplitude due to plasticity effects, thus confounding the assessment of cortical excitability. We tested whether short interpulse intervals (IPIs) affect TEP amplitude. Methods: We investigated possible changes in TEP amplitude and global mean field amplitude (GMFA) obtained with stimulation of the primary motor cortex at IPIs of 1.1-1.4 s in a group of healthy subjects. Results: We found no differences in TEP amplitude or GMFA between the first, second and last third of trials. Discussion: Short IPIs do not affect TEP size and can be used without the risk of confounding effects due to short-term plasticity.