Short-term plastic changes of the human nociceptive system following acute pain induced by capsaicin.
OBJECTIVE
To investigate possible neuroplastic changes induced by pain in cerebral areas devoted to nociceptive input processing.


METHODS
CO(2) laser-evoked potentials (LEPs) were recorded from 10 healthy subjects after stimulation of the right and left hand dorsum. Acute pain was obtained by topical application of capsaicin on the skin of right hand dorsum. LEPs were recorded after right and left hand stimulation before capsaicin, at the peak pain and 10-20 min after capsaicin removal. Right hand LEPs were evoked by laser stimuli delivered over the zone of secondary hyperalgesia during capsaicin and on both the zones of primary and secondary hyperalgesia after capsaicin removal.


RESULTS
After right hand stimulation, the vertex LEPs, which are generated in the cingulate cortex, were significantly decreased in amplitude during capsaicin application and after capsaicin removal. Moreover, the topography of these potentials was modified after capsaicin removal, shifting from the central toward the parietal region. Dipolar modelling showed that the dipolar source in the anterior cingulate cortex moved backward after capsaicin removal. All these changes were not observed after stimulation of the left hand, contralateral to the application of capsaicin, thus suggesting that functional changes are selective for the painful skin and the adjacent territories.


CONCLUSIONS
Our results suggest that acute cutaneous pain may inhibit the neural activity in regions of central nervous system processing nociceptive inputs and cortical representation of these inputs can be rapidly modified in presence of acute pain.
D000328:Adult; D001931:Brain Mapping; D002211:Capsaicin; D002540:Cerebral Cortex / Q000503:physiopathology*; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006225:Hand / Q000294:innervation / Q000503:physiopathology; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology; D007271:Injections, Intradermal; D028022:Low-Level Light Therapy / Q000379:methods; D008297:Male; D009433:Neural Inhibition; D010146:Pain / Q000139:chemically induced / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold; D011601:Psychophysics / Q000379:methods; D011930:Reaction Time; D012867:Skin / Q000187:drug effects; D013997:Time Factors
D002211:Capsaicin