Transcutaneous spinal direct current stimulation shows no effect on paired stimulation suppression of the somatosensory cortex

Jan H Bettmann,Christine H Meyer-Frießem,Peter K Zahn,Lauren M Schweizer,Lara Schlaffke,Martin Tegenthoff,Oliver Höffken

doi:10.1038/s41598-020-79131-2

Abstract

Transcutaneous spinal direct current stimulation (tsDCS) is a safe and convenient method of neuromodulation. It has been proven to alter sensory processing at cervicomedullary level by amplitude changes of the P30 response of tibial nerve somatosensory evoked potentials (TN SEPs). With knowledge that tsDCS affects cortical circuits, we hypothesized that tsDCS may also affect intracortical excitability of the somatosensory cortex assessed by paired stimulation suppression (PSS). Fourteen healthy men were included in this prospective, single-blinded, placebo-controlled crossover study. Single (SS) and paired stimulation (PS) TN SEPs were recorded over the scalp before, immediately as well as 30 and 60 min after applying 15 min of tsDCS over the twelfth thoracic vertebra. Each volunteer underwent three independent and randomized sessions of either cathodal, anodal or sham stimulation. tsDCS showed no effect on peak-to-peak amplitudes or latencies of cortical P40-N50 response after SS. Furthermore, tsDCS failed to induce significant changes on amplitude ratios of PSS, thus showing no impact on intracortical excitability of the somatosensory cortex in healthy subjects. Further research is required to reveal the different mechanisms and to strengthen clinical use of this promising technique.

Highlights

Transcutaneous spinal direct current stimulation is a safe and convenient method of neuromodulation
By analyzing tibial nerve somatosensory evoked potentials (TN SEPs), previous studies showed that anodal Transcutaneous spinal direct current stimulation (tsDCS) of the lower thoracic spine induces subcortical changes in the neural activity of the brainstem represented by an amplitude depression of the far field potential P30 recorded over the sixth cervical vertebra while cathodal tsDCS tends to increase P3015, both suggesting axonal alterations of transmission
One out of fifteen participants was excluded from further analysis due to electroencephalogram artefacts

Summary

Results

One out of fifteen participants was excluded from further analysis due to electroencephalogram artefacts. Independent from stimulation polarity (Fig. 1), participants did not report any adverse events due to tsDCS. No main effects of tsDCS were seen in amplitudes (polarity: F 1.88, 15.02 = 0.329, p = 0.712, partial η2 = 0.039; time: F1.55, 12.37 = 1.106, p = 0.345, partial η2 = 0.121). In latencies only a main effect over time was observed (polarity: F1.89, 15.15 = 0.32, p = 0.719, partial η2 = 0.038; time: F2.57, 20.53 = 5.837, p = 0.006, partial η2 = 0.422). No interactions between polarity*time were detected (amplitudes: F 3.16, 25.26 = 1.378, p = 0.272, partial η2 = 0.147; latencies: F3.33, 26.62 = 1.416, p = 0.259, partial η2 = 0.15). There were no effects of tsDCS polarity (F1.81, 14.48 = 0.886, p = 0.424, partial η2 = 0.1) or over time (F1.4, 11.21 = 4.021, p = 0.06, partial η2 = 0.334).

Discussion

Methods