SEPs were obtained after posterior tibial nerve stimulation at the ankles. Activity was measured at the popliteal fossa (popliteal potential, N9), at the first lumbar vertebra referred to the umbilicus (spinal potential, N22), at the sixth cervical vertebra referred to Fpz (cervico-medullary potential, P30) and at Cz referred to the right earlobe (cortical potential, P39). The amplitude and latency for each SEP component were measured at two time points (B, before spinal tDCS; T20, 20 min after spinal tDCS offset). From the top, pairs of traces are P39, P30, N22 and N9. In each pair, the top trace is the baseline recording (B), whereas the bottom trace is recorded 20 min after DC offset (T20). Note that anodal spinal tDCS (2.5 mA, 15 min) decreases the amplitude of the cervico-medullary potential (P30, second pair of traces from the top, grey lines). Conversely spinal tDCS leaves the other potentials unchanged. Modified from Cogiamanian et al. , with permission.