EPICURUS: E-field-based spatial filtering procedure for an accurate estimation of local EEG activity evoked by Transcranial Magnetic Stimulation

Background

The concurrent use of Transcranial magnetic stimulation (TMS) with electroencephalography (EEG) is increasingly integrated in research and clinical protocols to provide proof of effect by magnetic pulses. However, a reliable identification of evoked local EEG activity over TMS targeted cortical sites remains still challenging.

Methods

Here we present EPICURUS, a novel EEG spatial filtering approach, by which, individual MRI based simulations of TMS- electrical fields (E-fields) guide the reconstruction of TMS evoked o EEG signals originated in the primary motor cortex, minimizing crosstalk from non relevant more distant sources.

Results

A reduction of late Transcranial Evoked-Potentials (TEPs) components (>100 ms post pulse onset) suggest our E-field-based spatial filter approach efficiently reduced intrusion of non-locally relevant distant sources engaged by TMS, particularly when combined with a suppression of auditory entries.

Conclusion

The individually customized E-field-based spatial filtering procedure here developed for TMS- EEG datasets shows promise improving the spatio-temporal mapping of primary sources activated by magnetic pulses.

HIGHLIGHTS

• Concurrent TMS-EEG recordings are a well-established tool to monitor brain state of activity and provide proof of effect and target engagement.

• The lack of spatial specificity of EEG prevents an accurate estimation of the locally activated EEG sources, hindering the interpretation of TMS effects.

• We here developed a spatial filtering approach for TMS-EEG based on individual estimation of E- field spread following stimulation.

• Our E-field spatial filter combined with auditory constraints reduced non-relevant distant signal components and improved the reliability of local EEG estimates.