Projecting out muscle artifacts from TMS-evoked EEG

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG) is vital for studying brain excitability and connectivity.
• Stimulating areas near cranial muscles generates significant artifacts in EEG signals, obscuring early brain responses.

Purpose of the Study:

• To present and validate a novel method for removing muscle artifacts in TMS-EEG recordings.
• To improve the signal-to-artifact ratio for clearer analysis of cortical activity.

Main Methods:

• Artifact removal by projecting out topographic patterns of muscle activity.
• Muscle activity topographies identified using principal component analysis on high-pass filtered (100 Hz cutoff) data.
• Projection of principal components explaining high-frequency data variance to reduce both high- and low-frequency muscle artifacts.

Main Results:

• The method effectively reduced muscle artifacts, particularly in simulations involving Broca's area stimulation.
• A significant brain signal contribution remained after artifact removal.
• Signal-to-artifact ratio improvement ranged from 10- to 100-fold, depending on the number of projections used.

Conclusions:

• The proposed artifact removal technique enables reliable investigation of cortical states during TMS near cranial muscles.
• This method enhances the utility of TMS-EEG for neuroscientific research.