Event-related fMRI with single mechanical pain

A description of the functional anatomy of human pain processing has been subject to number of difficulties. We sought to resolve some these issues by using event-related functional magnet resonance imaging (ERfMRI). We gave single-painful stimuli at approximately 20 second intervals and averaged the resultant haemodynamic response functions. We found activation with ERfMRI in contralateral SI, both SII, the posterior cingulate cortex (PCC) and the contralateral dorsomedial thalamus. SI corresponds to the upper face represented by Penfield's map. The SII activation is more lateral than that obtained by others for the arm and foot. Significantly there was no activation of the anterior cingulate cortex (ACC) which has been an invariable site of activation with repetitive or blocked stimulation. Deactivations were found in the ipsilateral dorsomedial thalamus and ipsilateral SI. We believe these results define the functional anatomy of pain processing from the fact that is relatively devoid of contamination by the effects of habituation or elaborated emotional responses.