Biomagnetic signals recorded during transcranial magnetic stimulation (TMS)-evoked peripheral muscular activity

Abstract

Transcranial magnetic stimulation (TMS) has widespread clinical applications from diagnosis to treatment approaches. We combined TMS with non-contact magnetic detection of TMS-evoked muscle activity in peripheral limbs to explore a new diagnostic modality that enhances the utility of TMS as a clinical tool by leveraging technological advances in magnetometry. We recorded measurements inside of a hospital using an array of optically pumped magnetometers (OPMs) inside a portable shield that encompasses only the forearm and hand of the subject. We present magnetomyograms (MMG)s of TMS-evoked movement in a human hand, together with a simultaneous surface electromyograph (EMG) and electroencephalograph (EEG) data. The biomagnetic signals recorded in the MMG provides detailed spatial and temporal information that is complementary to that of the electric signal channels. Moreover, we identify features in the magnetic recording beyond that of the EMG, at time points which we further analyze in the EEG. This system demonstrates the value of biomagnetic signals in TMS-based clinical approaches and widens its availability and practical potential.

Sensitive magnetometry in challenging environments

“…As magnetometers themselves become smaller and more portable, so should the shielding solutions. We have recently detected transcranial magnetic stimulation (TMS)-evoked muscle activity inside a hospital setting [46] utilizing a portable shield which only encompasses the forearm and hand of the subject [47] (Fig. 4).…”