The effects of A-fiber pressure block on perception and neurophysiological correlates of brief non-painful and painful CO2 laser stimuli in humans.
(2003) European Journal of Pain — Vol. 7, n° 2, p. 189-199 (2003)
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- This study examined the relative capacity of Adelta- and C-fibers to encode non-painful and painful brief CO(2) laser stimuli by comparing the effects of Adelta/C-fiber activation versus C-fiber activation alone. In nine normal subjects, brief CO(2) laser pulses of four different intensities (range 5.8-10.6mJ/mm(2)) were delivered at random on the first intermetacarpal zone of the dorsum of the hand. A-fiber pressure block of the superficial radial nerve was performed to fully isolate the activity of C-fibers. Quality and intensity (VAS) of percepts, reaction time (RT) and laser-evoked potentials (LEPs) were examined in baseline and A-fiber block conditions. During A-fiber block, absolute detection threshold increased dramatically from 4.8+/-1.8 to 10.9+/-4.8mJ/mm(2), proportion of detected stimuli decreased from 87% to 47% and proportion of pain reports from 39% to 10%. The quality of sensations became mainly 'light touch' and the 'pricking' sensation almost vanished. The stimulus-VAS curve shifted to the right and the slope was reduced. Signal Detection Theory analysis revealed that discrimination performance (P(A)) was significantly depressed and that response bias (B) evolved from a neutral towards a stoical attitude. Median RT increased from 492 to 1355ms. The late LEPs, attributed to the activation of Adelta-fibers, disappeared and ultra-late LEPs were recorded at Cz with a positivity peaking around 800ms. Collectively, these observations lead to the conclusion that Adelta-fibers are the main peripheral mediators for the perception of brief CO(2) laser stimuli and that they provide more sensory information than C-fibers.
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Nahra, H., & Plaghki, L. (2003). The effects of A-fiber pressure block on perception and neurophysiological correlates of brief non-painful and painful CO2 laser stimuli in humans. European Journal of Pain, 7(2), 189-199. https://doi.org/10.1016/S1090-3801(02)00099-X (Original work published 2003)