Enhancing the effect of repetitive I-wave paired-pulse TMS (iTMS) by adjusting for the individual I-wave periodicity

Background: Repeated application of paired-pulse TMS over the primary motor cortex (M1) in human subjects with an inter-pulse interval (IPI) of 1.5 ms (iTMS(1.5) (ms)) has been shown to significantly increase paired-pulse MEP (ppMEP) amplitudes during the stimulation period and increased single-pulse MEP amplitudes for up to 10 minutes after termination of iTMS. Results: Here we show in a cross-over design that a modified version of the iTMS(1.5) (ms) protocol with an I-wave periodicity adjusted to the individual I1-peak wave latency (iTMS(adj)) resulted in a stronger effect on ppMEPs relative to iTMS(1.5) (ms). Conclusions: Based on these findings, our results indicate that the efficiency of iTMS strongly depends on the individual choice of the IPI and that parameter optimization of the conventional iTMS(1.5) (ms) protocol might improve the outcome of this novel non-invasive brain stimulation technique.