Selective Stimulation of C Fibers by an Intra-Epidermal Needle Electrode in Humans

We recorded evoked potentials (EPs) induced by intra-epidermal electrical stimulation using a needle electrode with specific parameters. We identified the fibers activated by this specific stimulation by assessing the conduction velocity (CV) of the peripheral nerve. The EPs were recorded from the Cz electrode (vertex) of the International 10-20 system in ten healthy male subjects. The dorsum of the left hand and forearm were stimulated with an intensity of 0.01 mA above the sensory threshold. The mean P1 latency of EPs for the hand and forearm were 1007 ± 88 and 783 ± 80 ms, respectively, and the CV estimated from the latency of P1 was 1.5 ± 0.7 m/s. The CV indicated that the fibers activated by the stimulation were C fibers. Since the method of stimulation is convenient and non-invasive, it should be useful for investigating the functions of small fibers.