Preferential stimulation of Aδ fibers by intra-epidermal needle electrode in humans

Abstract

We recorded evoked potentials (EPs) induced by conventional transcutaneous electrical stimulation (TS), laser stimulation (LS) and epidermal electrical stimulation (ES) using a specially made needle electrode. We evaluated the activated fibers by epidermal stimulation by assessing the conduction velocity (CV) of the peripheral nerves. The EPs were recorded from Cz electrode (vertex) of the International 10-20 system in 12 healthy subjects. For the ES, the tip of a stainless steel needle electrode was inserted in the epidermis of the skin (0.2 mm in depth). Distal and proximal sites of the upper limb were stimulated by the LS and ES with an intensity which induced a definite pain sensation. Similar sites were stimulated by TS with an intensity of two times the sensory threshold. A major EP positive response (P1) was obtained by stimulation by all three types of stimuli. The P1 latency for the TS (245+/-22 ms) was significantly shorter than that for the ES (302+/-17 ms, P<0.0001) and LS (341+/-21 ms, P<0.0001) and the peak latency P1 by the LS was also significantly longer, approximately 40 ms, than that by the ES (P<0.0001). The CVs were 15.1, 15.3 and 44.1 m/s obtained by ES, LS and TS, respectively. The CV indicated that the fibers activated by the ES were mainly A fibers, which corresponded to the fibers stimulated by the LS. We considered that the ES with our newly developed needle electrode was a very convenient method for the selective stimulation of the A fibers, since it was very simple, not requiring any special apparatus, did not cause bleeding or burns and caused minimum uncomfortable feeling.

Somatosensory-evoked potentials indicate increased unpleasantness of noxious stimuli in response to increasing stimulus intensities in the rat

“…In conclusion, the SEP components in the latency range studied in the present study are considered to be related to nociception which is in line with other studies using SEPs evoked by electrical stimulation to study nociception [7,15,35,[39][40][41][42][43].…”

An inhibitory interaction of human cortical responses to stimuli preferentially exciting Aδ or C fibers

“…The neurophysiological characteristics of the cortical responses to these stimuli were nearly identical to those reported by Inui et al (Inui et al, 2002) and by Granovsky et al (Granovsky et al, 2005) for Aδ and C fiber mediated evoked potentials. The cortical response to preferential Aδ or C fiber stimulation was suppressed whenever either cortical response preceded the other.…”

Analgesia to pressure–pain develops in the ipsilateral forehead after high- and low-frequency electrical stimulation of the forearm

“…Electrodes with these properties preferentially activate superficial nociceptive A-δ and C fibers (Inui et al 2002;Kaube et al 2000;Nilsson and Schouenborg 1999). The electrical detection threshold (EDT) was determined using the method of limits for 2 ascending and 2 descending sets of single pulses at 2 ms pulse width and an inter-pulse interval of 5 s. The stimulus intensity, starting at 0.1 mA, increased in steps of 0.1 mA until the participant perceived the stimulus, and then decreased in steps of 0.05 mA until the stimulus was no longer perceived.…”