Statistical analysis
pain
Before testing for effects of tsDCS modality, Shapiro–Wilk-tests for normal distribution, as well as tests for group effects and carry-over effects were performed. Because not all variables were normally distributed in all measurements, nonparametric tests were used to check for group effects, comparing 4 groups denoted in Fig. After this, tests for carry-over-effects were performed. For this, we followed a procedure recommended in the literatureTo evaluate effects of tsDCS modality on the different dependent variables, the values measured before tsDCS were first subtracted from the values measured after tsDCS in order to obtain the difference. The difference for each measured quantity (N1P1-amplitude, N1-latency, NRS value of the PREP-induced pain, DT, PT for PREP and NP-amplitude, N-latency, current intensity used for SEP) was then used as dependent variable in an ANOVA with the independent variables 'stimulation' (sham stimulation or anodal tsDCS) and 'limb' (lower or upper limb) in order to evaluate how the dependent variables changed during an experimental session depending on stimulation type, for upper and lower limb. The decision to use an ANOVA although not all variables were normally distributed for all measurements was made because the number of subjects was seen as large enough to guarantee a sufficient robustness to deviations from normal distributions, which is supported by previous studies