Channel interpolation in TMS-EEG: a quantitative study towards an accurate topographical representation.

The co-registration of transcranial magnetic stimulation and electroencephalography (TMS-EEG) is emerging as a successful technique for causally exploring cortical mechanisms and connections. However, various artefacts could affect TMS-EEG signals. Correct artefacted channels reconstruction is crucial to obtain accurate topographical representation and consequently accurate inverse problem solution, in order to map in a proper way the global brain responses after the stimulation of one particular brain region of interest. In this paper, we discuss the problem of artefacted channels interpolation in TMS-EEG signals. Aim of the study was to investigate two different interpolation methods evaluating their performance in two datasets: one constituted by 19 EEG channels montage (low-density spatial resolution) and the other one by 60 EEG channels montage (high-density spatial resolution). In addition, these evaluations took place in two different contexts of application: after the averaging of TMS Evoked Potentials (TEPs) in a time interval to obtain a global information in the considered range, and at fixed latencies 100 ms and 300 ms after the TMS stimulus. The results showed that the global reconstruction error was lower at fixed latencies for the high-density electrodes spatial resolution montage.