Data processing
Because this study focused on the response of N20m, we applied a band pass filter (6–200 Hz) to the preprocessed data using MNE-Python (v0.20) (We compared neural responses (P20m rate and non-response rate) and early somatosensory cortical processing (N20m amplitude, cross-correlation value, and gamma response) between patients with MD and controls. Using source waveforms obtained from equivalent current dipole modeling, we estimated the locations and activation strengths of the neural generators of N20m.We performed the following three steps to estimate the SI function accurately: First, we needed to select the MEG sensor that best reflected the SI function. This is because data analysis is significantly affected by the choice of the sensor. We selected the sensor with the highest similarity of the averaged sensor SEFs to the source waveform reflecting neural activity in the SI, using the cross-correlation between the sensor SEFs and source waveform at N20 peak latency ± 3.0 ms. N20m amplitudes of the source waveform were highly correlated with those of the sensor SEFs (Second, we analyzed the SEFs under the restricted vicinity of the N20m peak (peak latency ± 3.0 ms). This is because N20m is a very stable response and is unaffected by the conscious state (To quantify the reproducibility of N20m at single-trial responses in the selected sensor, we calculated the cross-correlation in the N20m peak latency ± 3.0 ms between the average sensor SEFs and SEFs at each single-trial epoch. Single-trial epochs were classified into three categories according to the cross-correlation of the individual epochs. For the N20m peak at SEFs, we defined cross-correlation of > 0.2, between − 0.2 and 0.2, and <  − 0.2 as N20m, non-response, and P20m epochs, respectively (Analysis of SEFs. The cross-correlation was calculated between the averaged sensor SEFs and SEFs at single-trial epochs in the N20m peak latency ± 3.0 ms. Three categories of single-trial epochs based on the cross-correlation of individual epochs were determined as follows: N20m, P20m, and non-response epochs. For the N20m peak at SEFs, we defined a cross-correlation of > 0.2, −0.2 to 0.2, and <  − 0.2 as N20m (green zone), non-response (yellow zone), and P20m epochs (orange zone), respectively (We estimated the N20m amplitude in the averaged sensor SEFs and gamma response at the single-trial epochs excluding non-response epochs. The positive value of the N20m amplitude was defined as the deflection of N20m from baseline. To assess the gamma response, each raw single-trial epoch was analyzed by the Morlet wavelet-based time–frequency analysis from 6 Hz to 200 Hz at 1-Hz steps (