Cortical responses to C-fiber stimulation by intra-epidermal electrical stimulation: An MEG study

• Published in: Neuroscience letters 2014-06, Vol.570, p.69-74
• Main Authors: Motogi, Jun, Kodaira, Minori, Muragaki, Yoshihiro, Inui, Koji, Kakigi, Ryusuke
• Format: Article
• Language: English
• Subjects: Adult; Brain Mapping; C-fiber; Cerebral Cortex - physiology; Electric Stimulation; Epidermis - innervation; Female; Foot - innervation; Humans; Intra-epidermal electrical stimulation; Magnetoencephalography; Male; Middle Aged; Nerve Fibers, Unmyelinated - physiology; Primary somatosensory cortex; Reaction Time; Secondary somatosensory cortex; Sensory Thresholds; Somatosensory Cortex - physiology
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2014.04.001

•Cortical responses to C-fiber stimulation were recorded using MEG.•For C-fiber stimulation, modified intra-epidermal electrical stimulation was used.•Six out of seven subjects reported the evoked sensation as pricking.•The conduction velocity calculated using S1 and opercular activation was 1.0m/s. Intra-epidermal electric stimulation (IES) is an alternative to laser stimulation for selective activation of cutaneous Aδ-fibers. IES is based on the fact that nociceptive fiber terminals are located in the epidermis, whereas receptors of other fibers end deep in the dermis. IES can selectively stimulate C-fibers if the electrode structure and stimulation parameters are carefully selected. However, stable selective stimulation of C-fibers using IES has proven difficult and cannot currently be used in clinical settings. The purpose of the present study was to determine if IES performed using a modified electrode reliably stimulates C-fibers. Magnetoencephalographic responses to IES to the foot were measured in seven healthy subjects. IES elicited somatosensory evoked fields in all subjects. The mean peak latency was 1327±116ms in the opercular region contralateral to the stimulated side, 1318±90ms in the opercular region ipsilateral to the stimulated side, and 1350±139ms in the primary somatosensory cortex. These results indicate that IES performed using the modified electrode can selectively stimulate C-fibers and may be a useful tool for pain research as well as clinical evaluation of peripheral small fiber function.