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

Abstract Background: The concurrent use of Transcranial magnetic stimulation (TMS) with electroencephalography (EEG) is increasingly integrated into research and clinical protocols. However, a reliable isolation of EEG responses that are locally evoked by TMS at the targeted cortical sites remains challenging. Methods: We introduce EPICURUS, a novel spatial filtering approach for TMS-EEG that uses individualized MRI-based simulations of the TMS-induced electric field (E-field) to define the spatial extent of locally evoked activity. This method guides the reconstruction of EEG signals originating from the primary stimulation site while minimizing crosstalk from distant, non-targeted sources. Results: Application of EPICURUS revealed a marked reduction in late transcranial evoked potential (TEP) components (>100 ms), indicating that E-field-based spatial filtering effectively suppresses contributions from indirect or multisensory sources, particularly when combined with auditory suppression techniques. Conclusion: By leveraging the spatial precision of individualized E-field modeling, EPICURUS enhances the specificity of EEG signal reconstruction, offering a promising tool for improving the spatiotemporal resolution of cortical responses directly evoked by TMS.