Differential inhibitory effect on human nociceptive skin senses induced bylocal stimulation of thin cutaneous fibers

It is known that stimulation of thin cutaneous nerve fibers can induce long lasting analgesia through both supraspinal and segmental mechanisms, the l atter often exhibiting restricted receptive fields. On this basis, we recen tly developed a new method, termed cutaneous field stimulation (CFS), for l ocalized stimulation of A delta and C fibers in the superficial part of the skin. In the present study, we have evaluated the effects of CFS on non-no ciceptive and nociceptive skin senses. We compared the effects of CFS with those of conventional transcutaneous electrical nerve stimulation (TENS), k nown to preferentially activate coarse myelinated fibers. A battery of sens ory tests were made on the right volar forearm of 20 healthy subjects. CFS (16 electrodes, 4 Hz per electrode, 1 ms, up to 0.8 mA) and TENS (100 Hz, 0 .2 ms, up to 26 mA) applied either on the right volar forearm (homotopicall y), or on the lower right leg (heterotopically) were used as conditioning s timulation for 25 min. The tactile threshold was not affected by either hom o- or heterotopical CFS or TENS, The mean thresholds for detecting warming or cooling of the skin were increased by 0.4-0.9 degrees C after homo- but not heterotopical CFS and TENS. Regarding nociceptive skin senses, homo- bu t not heterotopical CFS, markedly reduced CO2-laser evoked A delta- and C f iber mediated heat pain to 75 and 48% of control, respectively, and mechani cally evoked pain to 73% of control. Fabric evoked prickle, was not affecte d by CFS. Neither homo- nor heterotopical TENS induced any marked analgesic effects. It is concluded that different qualities of nociception can be di fferentially controlled by CFS. (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.