Cerebral responses to pain in patients suffering acute post-dental extraction pain measured by positron emission tomography (PET)

Previous studies with normal volunteers have demonstrated distributed cortical responses to experimental heat pain within a network of structures. The network includes the insula, anterior cingulate: prefrontal, inferior parietal and somatosensory cortices. Patients suffering from chronic nociceptive pain following rheumatoid arthritis (RA) have shown damped central responses to experimental heat pain applied to the back of the right hand. In this study of patients with acute, left-sided, post-molar-extraction (surgical) pain, we assessed the cortical responses to experimental heat pain, applied to the back of the right hand, using positron emission tomography (PET), and compared the responses with a previously reported control group and the RA group. In response to the experimental heat pain, the surgical group indicated significantly increased regional cerebral blood flow in the prefrontal cortex [Brodman's area (BA) 44] ipsilateral to the heat stimulus. Contralateral increases were detected in the putamen and transverse temporal gyrus (BA 40/41/42) with bilateral increases in the insular cortex. Compared to the control and RA group, there were significantly reduced responses in the anterior cingulate (BA 24), pre-frontal medial, and orbito-frontal (BA 9/10/32/47) cortices. These results suggest that relatively discrete regions of the cerebral cortex are responsible for acute nociceptive processing during an acute inflammatory episode. The reduced frontal and anterior cingulate responses to the experimental heat pain (applied to the right hand) during acute inflammatory pain (left jaw) illustrates cortical modulation of nociceptive processing that may be related to non-somatotopic, bilateral, nociceptive inputs to these areas.