Abstract
In this study, the neural response to pulse-width modulated (PWM) transcranial magnetic stimulation (TMS) is estimated using a computational neural model which simulates the response of cortical neurons to TMS. The recently introduced programmable TMS uses PWM to approximate conventional resonance-based TMS pulses by fast switching between voltage levels. The effect of such stimulation on the six cortical layers is modelled by estimating the activation threshold of the neurons. Modelling results are compared between the novel device and that of conventional TMS stimuli generated by Magstim stimulators. The neural responses to the PWM pulses and the conventional stimuli show a high correlation, which validates the use of pulse-width modulated pulses in TMS.Clinical Relevance- This computational modelling study demonstrates an equivalent effect of PWM and conventional TMS pulses on the nervous system which paves the way to more flexibility in exploring and choosing stimulation parameters for TMS treatment.
Highlights
Transcranial magnetic stimulation (TMS) is a non-invasive technique that uses the fundamental principles of magnetic induction to modulate the nervous system
Monophasic stimuli have lower thresholds when applied in the posterioranterior current direction, while biphasic stimuli have lower thresholds when their initial current direction is in the anterior-posterior direction, due to their dominant second phase
Morphological neural models integrated with transcranially induced electric fields are used to directly compare the neural response to pulse-width modulated TMS versus conventional TMS pulses
Summary
Transcranial magnetic stimulation (TMS) is a non-invasive technique that uses the fundamental principles of magnetic induction to modulate the nervous system. TMS is a useful tool to study the brain and to treat various psychiatric and neurological disorders [2]. Conventional TMS devices usually generate damped cosine pulses defined by the resonance period of the circuit, which limits the possible pulse shapes and patterns. Our group has developed a novel TMS device called the programmable TMS (pTMS), which employs pulse-width modulation (PWM) to rapidly switch between voltage levels, generating magnetic pulses of arbitrary shapes [3]. A second-generation device using cascaded H-bridges can generate five different voltage levels and deliver higher maximum energy.
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