Clark, S. R. | bioRxiv Science

bioRxiv2026

Characterising and Minimising Step and Filtering Artifacts in TMS-EEG Recordings

Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) enables direct measurement of cortical reactivity via TMS-evoked potentials (TEPs). Interpretation of early TEP components however, is highly sensitive to stimulation and hardware-related artifacts. We identified and characterised a persistent, non-neural step-drift artifact unexpectedly present in recent TMS-EEG recordings from our group. We show that the artifact is distinct from previously described TMS pulse and discharge/decay artifacts and likely reflects a hardware interaction phenomenon. We demonstrated that amplifier settings, but not TMS pulse shape, substantially influenced artifact expression, with DC-coupled recordings with no online high-pass filter reducing step amplitude compared with AC-coupled recordings with a high-pass filter. Simulations additionally revealed that filtering over the step-drift artifact introduced pronounced ringing and edge artifacts, highlighting the need to address this artifact prior to data processing. We propose a processing pipeline incorporating robust polynomial detrending and a modified Butterworth filter with autoregressive extrapolation that minimised TEP distortion in both simulated and real data containing the step-drift artifact. Together, these findings provide practical recommendations for both preventing and correcting step-drift artifacts and underscore the need for formal definition and routine recognition of this artifact to improve reproducibility and data quality in TMS-EEG research.

neuroscience↗

bioRxiv2025

Investigating the Influence of Anti-Seizure Medications on Aperiodic EEG Activity

ObjectiveElectroencephalography (EEG) signals comprise both oscillatory (periodic) and non-oscillatory (aperiodic) components. Aperiodic activity forms the 1/f-like background of the EEG power spectrum and can be characterised by parameters describing the offset and slope (1/f exponent). This study examined the effects of two antiseizure medications (ASMs), which reduce cortical excitability through different mechanisms of action, on aperiodic and periodic EEG activity. MethodsResting EEG was recorded with eyes open and closed from 13 healthy male volunteers at baseline and two hours after administration of lamotrigine (300 mg), levetiracetam (3000 mg), or placebo. Power spectra were computed using Welchs method. Aperiodic parameters were estimated using the specparam algorithm, and periodic activity was quantified after subtraction of the aperiodic component. ResultsIn the eyes-open condition, lamotrigine significantly reduced both aperiodic offset and exponent relative to placebo, consistent with a flattening of the aperiodic spectrum, whereas levetiracetam reduced the exponent without significantly altering the offset. Neither drug significantly altered aperiodic exponent or offset during eyes-closed. Lamotrigine reduced corrected theta power in both conditions and alpha power during eyes-open, whereas levetiracetam increased beta power in both conditions and reduced gamma power during eyes-closed. ConclusionsBoth lamotrigine and levetiracetam altered aperiodic and periodic EEG activity, with aperiodic effects observed only during eyes-open. SignificanceAperiodic EEG measures may provide a non-invasive approach for characterising ASM-related neurophysiological effects and may help elucidate how distinct pharmacological mechanisms influence large-scale cortical activity.

neuroscience↗