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

Naofumi Otsuru1, 2, *, Koji Inui1, Koya Yamashiro1, 2, Takahiro Miyazaki1, 2, Ichiro Ohsawa3, Yasuyuki Takeshima1, Ryusuke Kakigi1, 2
1 Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan
2 Department of Physiological Sciences, School of Life Sciences, Graduate University for Advanced Studies, Hayama, Kanagawa, Japan
3 The first Department of Surgery, Mie University School of Medicine, Tsu 514-8507, Japan

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© 2009 Otsuru et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of IntegrativePhysiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Tel: +81 564 55 7811; Fax: +81 564 52 7913; E-mail:


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.