The rt-TEP tool: real-time visualization of TMS-Evoked Potentials to maximize cortical activation and minimize artifacts

Background: The impact of transcranial magnetic stimulation (TMS) on cortical neurons is currently hard to predict based on a priori biophysical and anatomical knowledge alone. Lack of control of the immediate effects of TMS on the underlying cortex can hamper the reliability and reproducibility of protocols aimed at measuring electroencephalographic (EEG) responses to TMS.New Method: We introduce and release a novel software tool labelled rt-TEP (real-time TEP). This tool interfaces with different EEG amplifiers and offers a series of informative visualization modes to assess the magnitude of the initial brain response to TMS and the overall quality of TMS-evoked potentials (TEPs) in real time.Results: We show that rt-TEP can be used to detect -and thus abolish or minimize -magnetic and muscle artifacts contaminating the post-stimulus period of single-trial data: this application affords a clear visualization and quantification of the amplitude of the early (8-50 ms) and local EEG response after averaging a limited number of trials. Such real-time readout can then be used to optimize TMS parameters (e.g., site, orientation, intensity) before data acquisition to obtain TEPs characterized by high signal-to-noise ratio.Comparison with Existing Methods: The ensemble of real-time visualization modes of rt-TEP are not currently implemented in any available commercial software and provide a key readout to titrate TMS parameters beyond the a priori information provided by biophysical and anatomical models.Conclusions: Real-time optimization of TMS parameters to achieve a desired level of initial activation can facilitate the acquisition of reliable TEPs and can improve the reproducibility of data collection across laboratories.