Electrical low-frequency stimulation induces long-term depression of sensory and affective components of pain in healthy man

Electrical low-frequency stimulation (LFS) of nociceptive skin afferents reliably induces long-term depression (LTD) of pain. Recent experiments have assessed the effects of LTD on pain perception by using a simple one-dimensional rating scale. The psychophysical study investigated the impact of noxious LFS on the sensory and affective aspects of pain perception by multidimensional rating scales. In 20 healthy volunteers, nociceptive fibers of the left hand dorsum were electrically stimulated by a concentric electrode. Test stimulation series (15 stimuli each, 0.125 Hz) were performed before (Pre) and after (Post) a conditioning LFS (1 Hz, 20 min) or no stimulation period (Control). Pain ratings concerning test stimulation and LFS were obtained by multidimensional assessment including Verbal rating scale of perceived stimulus intensity (VRS-I) and unpleasantness (VRS-U) and pain perception scale with sensory (SES-S) and affective items (SES-A). After the conditioning LFS, VRS-I, VRS-U, SES-S, and SES-A decreased as compared to Pre series and Control. During conditioning LFS, ratings decreased. Factor analysis of SES-S revealed sole reduction of superficial sharp pain perception after conditioning LFS in contrast to Control experiment. Perception of deep rhythmic pain decreased over time. Deep constant pain and superficial heat pain were not affected. Electrical test stimulation via concentric electrode evokes sensory as well as affective pain perception. Both components decrease during noxious, conditioning LFS and remain depressed for at least one hour. Reduction of sharp pain points to A delta fiber mediated LTD. These results stress the analgesic potency of LTD and its possible impact on future therapy in chronic pain. (C) 2009 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.