Data analysis
BRAIN
Storage for offline analysis was achieved by a 32-channel-amplifier (Brain Amp, Brain Products, Germany; Bandwidth: 0.1 Hz–1 kHz; digitization sampling rate: 5 kHz). Employing Vision Recorder Version 1.03 offline analysis was carried out. For this, the data was segmented into epochs from 200 ms before and 800 ms after stimulus onset for data acquired during PREP measurements and epochs ranging from 30 ms before stimulus onset to 80 ms after stimulus onset for data acquired during SEP measurements.Following previous studies for PREP using CE40 stimuli were applied intending to make the potential of PREP as clear to detect as possible. After data from ongoing studies in the neurological department of the Bergmannsheil Bochum seemed to indicate a decrease of the N1P1-amplitude when using 40 stimuli (data not shown), we split the data into the epochs 2–20 (first half) and 21–40 (second half). The comparison showed that the data of the second half contained more artifacts due to body movements and blinking, as well as significantly smaller amplitudes (data not shown). Therefore, the second half of the data was discarded and only the average of epochs 2–20 was used in later analysis, as was previously the practiceIn the PREP measurement we determined the N1- and P1-peaks, calculated the N1P1-amplitude and documented the N1-latency of each potential, as described in previous studiesIn the SEP measurements, the evaluated potentials depended on the examined limb. For the upper limb (median nerve SEP), the amplitude of the N20-potential was subtracted from the amplitude of the P25-potential, resulting in the N20-P25-amplitude, and the latency of the N20-potential was measured. For the lower limb (tibial nerve SEP), the same operations were performed with the N30- and P40-potentials.Subjects with EEG recordings in which the N1-, P1- N20-, P25, N30- or P40-potentials could not be clearly identified due to artifacts (e.g., movement or electrode artifacts) during at least one of the time points of the study, were excluded from further analysis.