Using a Double-Coil TMS Protocol to Assess Preparatory Inhibition Bilaterally

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) measures corticospinal excitability (CSE) via motor-evoked potentials (MEPs).
• Current methods typically use single-coil TMS on one M1, limiting simultaneous CSE assessment in both limbs.
• Previous work demonstrated that double-coil TMS (double-coil_{1 ms} TMS) can elicit comparable MEPs in both hands at rest.

Purpose of the Study:

• To evaluate the efficacy of double-coil_{1 ms} TMS for assessing CSE during a motor task.
• To determine if double-coil_{1 ms} TMS can detect the transient motor inhibition characteristic of action preparation.
• To compare the reliability of double-coil_{1 ms} TMS versus single-coil TMS in measuring MEP amplitude and variability during a task.

Main Methods:

• Participants performed an instructed-delay choice reaction time task.
• Motor-evoked potentials (MEPs) were elicited using either single-coil TMS or double-coil_{1 ms} TMS over bilateral M1 during the delay period.
• MEP amplitude and coefficient of variation (CV) were compared between baseline and the delay period for both stimulation types.

Main Results:

• MEPs showed significant suppression (reduced amplitude) and decreased variability (smaller CV) during the delay period compared to baseline.
• These inhibitory effects on MEPs were equivalent whether single-coil TMS or double-coil_{1 ms} TMS was applied.
• Double-coil_{1 ms} TMS successfully detected task-related changes in corticospinal excitability, similar to single-coil TMS.

Conclusions:

• Double-coil_{1 ms} TMS is a valid and reliable method for assessing corticospinal excitability (CSE) during motor preparation tasks.
• This technique allows for simultaneous measurement of CSE in both hands, expanding research possibilities.
• The findings support the use of double-coil_{1 ms} TMS for investigating the neurophysiological underpinnings of human behavior and motor control.