Common neural systems for contact heat and laser pain stimulation reveal higher-level pain processing.

Our current knowledge of pain-related neuronal responses is largely based on experimental pain studies using contact heat or nontactile laser painful stimulation. Both stimuli evoke pain, yet they differ considerably in their physical and perceptual properties. In sensory cortex, cerebral responses to either stimulus should therefore substantially differ. However, given that both stimuli evoke pain, we hypothesized that at a certain subset of cortical regions the different physical properties of the stimuli become less important and are therefore activated by both stimuli. In contrast, regions with clearly dissociable activity may belong to "lower-level" pain processing mechanisms depending on the physical properties of the administered stimuli. We used functional magnetic resonance (fMRI) to intraindividually compare pain-related activation patterns between laser and contact heat stimulation using four different intensities of laser and contact heat stimuli. Common and dissociable neural responses were identified by correlating perceived pain intensities with blood oxygenation level dependent (BOLD) signal changes. Only neuronal responses to stimuli that were perceived as painful were analyzed. Pain-related BOLD signal increases independent of stimulus modality were detected in the anterior insula, anterior cingulate cortex, medial secondary somatosensory cortex, and the prefrontal cortex. These similarities are likely to reflect higher-level pain processing, which is largely independent of the single physical parameters that determine the painful nature of the stimuli.