A 15-minute session of direct current stimulation does not produce lasting changes in axonal excitability

Abstract

To assess the applicability and lasting effects on axonal membrane excitability of transcutaneous peripheral nerve direct current stimulation (pDCS). We included 15 healthy subjects. pDCS was performed with the active electrode placed over the left forearm and the reference electrode on the back of the hand. We used 5×5cm rubber electrodes and the current applied was 2.5mA during 15minutes. Three pDCS sessions were performed on the same day with a 20-minute interval between them: first a sham stimulation, followed by cathodal and anodal stimulations in random order. Motor nerve excitability measurements were performed immediately after each pDCS session using the TRONDNF nerve excitability protocol of the QTRAC program. The protocol was completed and well tolerated in all subjects. There were no consistent significant differences in excitability measurements between the three sessions. No consistent long-lasting effects were noted on peripheral nerve excitability beyond the period of application of pDCS. We showed that a 15-minute session of DCS is not able to produce lasting changes in axonal excitability, supporting the hypothesis that the functional and clinical impact of DCS protocols applied to the central nervous system is related to long-term synaptic changes rather sustained local changes in axonal rest membrane potential.