Multi-locus transcranial magnetic stimulation with pulse-width modulation

Area of Science:

• Neuroscience
• Biomedical Engineering

Background:

• Transcranial magnetic stimulation (TMS) uses scalp coils to induce electric fields for neuronal activation.
• Multi-locus TMS (mTMS) allows electronic control of stimulation location and orientation.
• Current mTMS coil adjustments limit target changes to seconds.

Purpose of the Study:

• Investigate microsecond-scale pulse-width modulation (PWM) for rapid multi-coil TMS targeting.
• Assess PWM's efficacy in overcoming mTMS speed limitations.

Main Methods:

• Developed a methodology for generating and driving PWM approximations of reference pulses.
• Compared resting motor thresholds (RMTs) and motor evoked potentials (MEPs) between trapezoidal and PWM pulses.
• Evaluated performance across various multi-coil targeting scenarios.

Main Results:

• PWM pulses exhibited high temporal complexity.
• No significant differences in RMT or MEPs were found for 2- or 3-coil combinations.
• Five-coil PWM stimulation showed a 9% RMT increase (p=0.06) and 20% MEP amplitude decrease (p<0.05) at higher doses.

Conclusions:

• PWM pulses with mTMS are feasible for millisecond-scale target control.
• Motor responses were equivalent for trapezoidal and PWM pulses with 2-3 coils.
• Further research is needed on neurophysiological effects with increased coil counts.