Brain responses to pain have been widely investigated over the past 10 years through positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies. Experiments in which normal volunteers undergo brain scans during a painful experience have allowed investigators to perform precise spatial mapping of brain responses. Two meta-analyses that reviewed brain activations to nociceptive stimuli have clearly identified discrete brain regions where activation is consistently found during the application of noxious stimuli and/or the experience of pain (Derbyshire 2000; Peyron et al. 2000b). Thus, the question of which brain regions show pain-related changes in activity can now be answered within the framework of a relatively stable functional map and a limited number of activated brain regions. The questions of "when" brain areas are activated during pain and "what" is the functional contribution of those areas to pain cannot be so easily answered by PET and fMRI techniques.
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