Transcranial magnetic stimulation modulation of corticospinal excitability by targeting cortical I-waves with biphasic paired-pulses
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CitationKallioniemi, Elisa. Savolainen, Petri. Järnefelt, Gustaf. Koskenkorva, Päivi. Karhu, Jari. Julkunen, Petro. (2018). Transcranial magnetic stimulation modulation of corticospinal excitability by targeting cortical I-waves with biphasic paired-pulses. Brain Stimulation, 11 (2) , 322-326. 10.1016/j.brs.2017.10.014.
Transcranial magnetic stimulation (TMS) induced I-wave behavior can be demonstrated at neuronal population level using paired-pulses and by observing short-interval cortical facilitation (SICF). Advancements in stimulator technology have made it possible to apply biphasic paired-pulses to induce SICF.
Our aim was to characterize the SICF I-wave interaction by biphasic paired-pulses with the ultimate objective to enhance TMS effects via SICF in various TMS-applications.
We used biphasic paired-pulses in 15 volunteers to characterize corticospinal SICF using various 1.2–8.0ms inter-stimulus intervals, and measuring SICF input-output response.
SICF interaction with the first I-wave (I1) was observed in the output responses (motor evoked potentials; MEPs) in all subjects. Most subjects (≥80%) also exhibited later SICF I-wave interaction. SICF at I1 was present at all applied intensities below 140% of resting motor threshold. At I2, we observed SICF only with intensities just above motor threshold.
Biphasic paired-pulses can reliably induce SICF shown by the facilitatory I-wave interaction, and could therefore be applied with repetitive bursts to enhance responsiveness to TMS.