Topographic effects of tonic cutaneous nociceptive stimulation on human electroencephalograph.

To examine the specific effects of cutaneous pain on electroencephalographic (EEG) activities, tonic painful and non-painful sensations in left forearm were induced by intradermal injection of capsaicin 100 microg/20microl and the same volume of vehicle, respectively, in 15 healthy males. The EEG data acquired in five experimental conditions: (i) baseline A; (ii) non-painful vehicle injection; (iii) baseline B; (iv) painful capsaicin injection and (v) waning pain, were analyzed and compared with analysis of variance. Only the painful capsaicin injection evoked significant decreases of theta, alpha-1 and alpha-2 powers over the centro-parieto-occipital regions compared with baseline B. No significant difference in EEG activation between the non-painful vehicle injection and painful capsaicin injection was found. This implicates that the observed topographic EEG activation is not specific for pain but probably related to the cutaneous stimulation.