Noninvasive brain imaging: Brain correlates of the voluntary mental evocation of pain

Abstract

Pain is consistently associated with the activation of a network of cerebral structures including S1, S2, insula (INS), and anterior cingulate cortex (ACC). This study examines the role of these structures in the mental representation of pain during voluntary mental imagery. BOLD signal acquired in 7 healthy volunteers was contrasted in four conditions: pain stimulation (contact heat at 46.5-49.0°C); warm stimulation (38.0°C); mental imagery of pain; and mental imagery of warmth. The contact probe was applied on the left leg for 9s, every 18s, in all conditions. In the imagery conditions, the temperature remained neutral (32.0°C) and subjects were instructed to imagine a WARM sensation or a highly unpleasant heat PAIN experience when the thermode touched the skin. Directed searches were conducted specifically on the four contralateral target areas using group analyses (t>2.55, p-corrected<.05). Contrasts between pain and warm stimulation conditions confirmed pain-related activation (t-value) in the posterior ACC (4.41), the anterior (3.93) and posterior (6.71) INS, the parietal operculum (2.64), and the leg area of S1 (2.59). Imagery of pain compared to warm significantly activated the ACC (3.28) and the parietal operculum (3.93) while INS activation was only marginally significant (peak-t=2.47) and no peak was found in S1 (t<2.00). A conjunction analysis of the pain vs. warm contrast in the stimulation and imagery conditions further confirmed the common activation of the posterior ACC (3.04), the parietal operculum (3.04), and a marginally significant effect in the posterior INS (2.54). Separate conjunction analyses revealed additional activations common to the stimulation and imagery conditions in the anterior INS in both the pain (3.20) and warm (2.65) conditions and in the anterior ACC in the warm condition (3.61). These results are consistent with the involvement of pain-related cortical areas in the mental evocation and imagery of pain experiences.