Abstract
Transcranial magnetic stimulation (TMS) is a form of non-invasive brain stimulation commonly used to modulate neural activity. Despite three decades of examination, the generation of flexible magnetic pulses is still a challenging technical question. It has been revealed that the characteristics of pulses influence the bio-physiology of neuromodulation. In this study, a second-generation programmable TMS (xTMS) equipment with advanced stimulus shaping is introduced that uses cascaded H-bridge inverters and a phase-shifted pulse-width modulation (PWM). A low-pass RC filter model is used to estimate stimulated neural behavior, which helps to design the magnetic pulse generator, according to neural dynamics. The proposed device can generate highly adjustable magnetic pulses, in terms of waveform, polarity and pattern. We present experimental measurements of different stimuli waveforms, such as monophasic, biphasic and polyphasic shapes with peak coil current and the delivered energy of up to 6 kA and 250 J, respectively. The modular and scalable design idea presented here is a potential solution for generating arbitrary and highly customizable magnetic pulses and transferring repetitive paradigms.
Highlights
Transcranial Magnetic Stimulation (TMS) uses electromagnetic induction to modulate neural activity
The stimulation coil is positioned over the appropriate cortex site and a high voltage pulse is applied to it
Conventional TMS systems are limited by the lack of flexibility of their electrical architecture, and can only produce damped cosine pulses [1]
Summary
Transcranial Magnetic Stimulation (TMS) uses electromagnetic induction to modulate neural activity. It is used as both an FDA-approved treatment for depression and major depressive disorder [1] as well as an important diagnostic tool for neurological disorders. The induced magnetic field drives a brief current in the brain which either directly generates action potentials through depolarization or modifies the state of cortical excitability [2]. Altering stimulation parameters such as pulse magnitude and pulse rate gives increased flexibility to investigate the brain in a safe, non-invasive manner. The controllable TMS (cTMS) devices [3] can achieve a slightly wider variety of near-rectangular pulses by using insulatedgate bipolar transistors (IGBTs) to deliver variable width pulses
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