Urge to scratch represented in the human cerebral cortex during itch.

1. We used functional positron emission tomography (PET), measuring regional cerebral blood flow (rCBF) as an index of neuronal activity, to investigate the central processing of itch in 10 healthy volunteers subjected to intracutaneous injections of histamine. 2. The study has unraveled a central representation that depicts a motor intention of the urge to scratch contingent on the perception of unpleasant itch. The coactivation of the anterior cingulate cortex (ACC), supplementary motor area (SMA), premotor area (PM), and inferior parietal lobule (IPL) substantiates that the posterior sector of the ACC (Brodmann 24) is related to the sensorial/affectional aspect of the event. The premotor cortical areas (SMA, PM) and the IPL may participate in the preparation of an intended action.