Strengths and Limitations
pain
The greatest strength of the study is the elaborate sham-controlled, double-blind cross-over design using 4 time points and several measures of pain perception. However, this also makes multiple testing a larger problem, especially when effects are small. Indeed, our effects were significant only at an exploratory level. The sample size was principally adequate, even somewhat larger than that of previous studies that included 14 to 16 participants [There are several possible reasons why we found only small effects. The occipital bone over the cerebellum is very thick [In addition, individual differences may affect susceptibility to cerebellar t-DCS modulation of pain. For example, the effect of cerebellar t-DCS on pain perception and LEPs was blunted in subjects with high hypnotizability [Moreover, a single t-DCS session as used here and in previous experimental studies might be insufficient to induce a stable effect. Clinical studies showing t-DCS effects on pain perception use at least 5 sessions and often many more [In addition, it must be mentioned that the measures of endogenous pain modulation and supraspinal nociception used here only reflect facets of these phenomena and are subject to confounding. This may be especially evident for the electrophysiological measures. Both the RIII reflex and the N120 are not purely nociceptive, and the RIII reflex arch contains spinal interneurons and motor neurons [