P50-T Changes in peripheral nerve excitability by transcutaneous direct currents in healthy subjects – pilot study

Abstract

Background Anodal stimulation results in subthreshold depolarisation, while cathodal stimulation hyperpolarises neuronal membranes. There have been few studies on the possible modulatory effect of long lasting transcutaneous direct current stimulation on the axonal membrane properties of peripheral nerves, especially on the possible modulatory effect of such currents. We aimed to assess the applicability, safety and effects on axonal membrane excitability of transcutaneous peripheral nerve stimulation with direct currents (pDCS). Material and methods We included 15 healthy subjects. pDCS was performed with the active electrode placed over the forearm and the reference electrode on the back of the hand using 5 × 5 cm rubber electrodes. The current applied was 2.5 mA during 15 min. Following a sham stimulation, two different settings were randomly used, cathodal and anodal current. Excitability measurements were performed using the TRONDNF nerve excitability protocol of the QTRAC program. Results The protocol was completed and well tolerated in all subjects. The TEd (90–100 ms) was significantly lower for anodal stimulation (p = 0.04). There were no other significant differences. These results were not replicated in a repeated trial, and in addition multiTRAC assessment failed to demonstrate significant after-effects on excitability. Conclusions TEd 90–100 ms reflects function of slow K+ channels, mainly located at the nodes. Initial findings suggested that slow K+-channel expression or conductance may be reduced after the application of anodal DC current, however repeated studies and real-time assessment of excitability measures argue against a consistent effect. Further research should be performed, using different intensities and stimulation time, as well as other excitability measurements.