Psychophysical evidence for long-term potentiation of C-fiber and Adelta-fiber pathways in humans by analysis of pain descriptors.

Long-term potentiation of human pain perception (nociceptive LTP) to single electrical test stimuli was induced by high-frequency stimulation (HFS) of cutaneous nociceptive afferents. Numerical pain ratings and a list of sensory pain descriptors disclosed the same magnitude of nociceptive LTP (23% increase for >60 min, P < 0.001), whereas affective pain descriptors were not significantly enhanced. Factor analysis of the sensory pain descriptors showed that facilitation was restricted to two factors characterized by hot and burning (+41%) and piercing and stinging (+21%, both P < 0.01), whereas a factor represented by throbbing and beating was not significantly increased (+9%, P = 0.47). The increased perception of the burning pain quality for >1 h after HFS is interpreted as a LTP-like facilitation of the conditioned cutaneous C-fiber pathway. Additionally, the increase of the stinging pain quality supplied evidence for facilitation of a sharpness-sensitive Adelta-fiber pathway.