Parietal and cingulate processes in central pain. A combined positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) study of an unusual case

Parietal, insular and anterior cingulate cortices are involved in the proce ssing of noxious inputs and genesis of pain sensation. Parietal lesions may generate central pain by mechanisms generally assumed to involve the 'medi al' pain system (i.e. medial thalamic nuclei and anterior cingulate cortex (ACC)). We report here PET and fMRI data in a patient who developed central pain and allodynia in her left side after a bifocal infarct involving both the right parietal cortex (SI and SII) and the right ACC (Brodmann areas 2 4 and 32), thus questioning the schematic representation of cortical pain p rocessing. No rCBF increase was found in any part of the residual cingulate cortices, neither in the basal state (which included spontaneous pain and extended hypoperfusion around the infarct), nor during left allodynic pain. Thus, as previously observed in patients with lateral medullary infarct, n either spontaneous pain nor allodynia reproduce the cingulate activation ob served after noxious pain in normal subjects. Conversely, both PET and fMRI data argue in favour of plastic changes in the 'lateral discriminative' pa in system. Particularly, allodynia was associated with increased activity a nteriorly to the infarct in the right insula/SII cortex. This response is l ikely to be responsible for the strange and very unpleasant allodynic sensa tion elicited on the left side by a nonnoxious stimulation. (C) 2000 Intern ational Association for the Study of Pain. Published by Elsevier Science BV .