The Effect of Inter-pulse Interval on TMS Motor Evoked Potentials in Active Muscles

• Published in: Frontiers in human neuroscience Vol. 16; p. 845476
• Main Authors: Matilainen, Noora, Soldati, Marco, Laakso, Ilkka
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Research Foundation 22-03-2022; Frontiers Media S.A
• Subjects: active muscle contraction; Brain research; Cortex (motor); Electric fields; Electromyography; Human Neuroscience; inter-pulse interval; Magnetic fields; Mapping; Medical imaging; motor evoked potential; Motor evoked potentials; motor mapping; motor threshold; Muscle contraction; Simulation; TMS; Transcranial magnetic stimulation; inter-pulse interval; active muscle contraction; motor evoked potential; motor threshold; TMS; motor mapping
• ISSN: 1662-5161; 1662-5161
• DOI: 10.3389/fnhum.2022.845476

The time interval between transcranial magnetic stimulation (TMS) pulses affects evoked muscle responses when the targeted muscle is resting. This necessitates using sufficiently long inter-pulse intervals (IPIs). However, there is some evidence that the IPI has no effect on the responses evoked in active muscles. Thus, we tested whether voluntary contraction could remove the effect of the IPI on TMS motor evoked potentials (MEPs).
In our study, we delivered sets of 30 TMS pulses with three different IPIs (2, 5, and 10 s) to the left primary motor cortex. These measurements were performed with the resting and active right hand first dorsal interosseous muscle in healthy participants (
= 9 and
= 10). MEP amplitudes were recorded through electromyography.
We found that the IPI had no significant effect on the MEP amplitudes in the active muscle (
= 0.36), whereas in the resting muscle, the IPI significantly affected the MEP amplitudes (p < 0.001), decreasing the MEP amplitude of the 2 s IPI.
These results show that active muscle contraction removes the effect of the IPI on the MEP amplitude. Therefore, using active muscles in TMS motor mapping enables faster delivery of TMS pulses, reducing measurement time in novel TMS motor mapping studies.