The PET H 2 15 O-bolus method was used to image regional brain activity in normal human subjects during intense pain induced by intradermal injection of capsaicin and during post-capsaicin mechanical allodynia (the perception of pain from a normally non-painful stimulus). Images of regional cerebral blood flow were acquired during six conditions: (i) rest; (ii) light brushing of the forearm; (iii) forearm intradermal injection of capsaicin, (iv) and (v) the waning phases of capsaicin pain; and

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... vi) allodynia. Allodynia was produced by light brushing adjacent to the capsaicin injection site after ongoing pain from the capsaicin injection had completely subsided. Capsaicin treatment produced activation in many discrete brain regions which we classified as subserving four main functions: sensation-perception (primary somatosensory cortex, thalamus and insula); attention (anterior cingulate cortex); descending pain control (periaqueductal grey); and an extensive network related to sensory-motor integration (supplementary motor cortex, bilateral putamen