Subjective and brain-evoked responses to electrical pain stimulation: effects of cigarette smoking and warning condition.

Infrahuman studies employing behavioral indices of pain reactivity have supported a central antinociceptive action of nicotine which appears to be selective and dependent on the class of pain elicited. Human investigations employing subjectively based ratings and judgments of pain intensity have been less conclusive regarding the painfulness of stimuli following nicotine/smoking administration. As the more objective brain-evoked potential (EP) measure has been shown to reflect pain intensity and to be sensitive to a variety of analgesics, this study attempted to examine, together with subjective responses, the effects of cigarette smoking on EPs to pain stimuli administered under varying warning conditions. Twelve male and twelve female smokers served as experimental subjects. In smoking and nonsmoking sessions, subjective intensity ratings (SR) and vertex EPs were assessed in response to electrical skin stimuli presented at a level 20% above pain threshold. Stimulation was either nonwarned or warned with warning conditions involving single or repeated presentations of electrical current at constant or increasing intensities 12 seconds prior to pain stimulation. SRs and peak-to-peak N1-P2 EP amplitudes were measured for each smoking session and warning condition. A significant condition effect was observed for SRs with increasing prepain warning stimulation resulting in the greatest pain ratings. Although smoking did not directly alter SRs or EPs to pain, smoking exposure, as measured by carbon monoxide, was found to be differentially correlated with EP alterations in male and female smokers depending on the warning condition.