抄録
The A beta, A delta and C fibers are suggested to be selectively stimulated by sinusoidal current stimulation (SCS) at 2k, 250 and 5Hz, respectively. However no direct electrophysiological evidence has been reported. In this study, we examined the characteristics of the sensations and the afferent discharges evoked by the different frequencies of SCS by use of microneurography.Ten healthy volunteers with informed consent were used. A pair of surface gel electrodes (20x25 mm) was put around the middle finger for SCS. Subjective detection threshold and the characteristics of sensations elicited by the three different frequencies of SCS were recorded. Then a tungsten microelectrode was inserted to the medial nerve and unitary discharges of the afferents were recorded, and their conduction velocities and response to SCS were investigated.The mean of detection threshold (T) at 2k, 250 and 5Hz SCS were 1.8, 0.9 and 1.0 mA, and their major sensations provoked at 2T were pressing, tingling and pulsing, respectively. In microneurogram, the A beta fibers were clearly activated by 2kHz SCS and regular discharges about 30Hz appeared at twofold threshold intensity of firing. The A beta fibers were also activated relatively higher intensity of SCS at 250 or 5Hz. The activities of A delta and C fibers were not recorded. These results suggest that each frequency of SCS induced different sensation at relatively low intensity which may activate the afferent fibers in different way. [Jpn J Physiol 54 Suppl:S174 (2004)]
