[A potential role of functional magnetic resonance imaging in the diagnosis of pain].

Functional neuroimaging techniques have revealed the cerebral substrates of pain perception (pain matrix) in humans, which include the thalamus, as well as primary, secondary somatosensory, insular, anterior cingulate, and prefrontal cortices. Functional magnetic resonance imaging (fMRI) could be the most suitable candidate for routine clinical use in the evaluation of pain because of its relatively low cost and the absence of irradiation. Here the author summarizes the practical aspects of fMRI studies on pain, and proposes the "bottom-up/top-down theory" of cerebral pain processing that explains possible interaction among discrete parts of pain matrix. Long-term, plastic changes induced by such interaction could play a pivotal role in the exaggerated brain activity of chronic pain patients. The top-down component of pain matrix also explains basic neuroimaging findings on the anticipation, empathy, and placebo effects of pain, and on the cortical trigger of the descending pain inhibitory system. Finally, the author summarizes his recent research on the cerebral substrates of chronic low back pain, and shows a case study on neuropathic pain using fMRI, which hopefully should help in planning clinical fMRI studies for a longitudinal follow-up of chronic pain patients.