Functional imaging in pain research

Functional brain imaging techniques allow to noninvasively visualize neuronal activity and associated metabolic consequences. In combination with elegant experimental paradigms in both healthy volunteers and, increasingly, in patients, functional brain imaging has led to a vast accumulation of knowledge concerning the CNS mechanisms involved in pain perception and pain modulation in humans. The so-called "pain matrix" represents a dynamic network of cortical and subcortical brain regions regularly activated by acute pain. This includes the somatosensory cortices (SI, SII), insular cortex, the cingulate cortex, prefrontal areas, amygdala, thalamus, brainstem and cerebellum. The subjective perception of pain is substantially influenced by context-dependent intracortical modulations and the descending pain modulatory system. This system includes cingulo-frontal brain areas together with specific brainstem nuclei that can exert control over nociceptive input at the level of the dorsal horn of the spinal cord. Recent studies support the view that a dysfunctional interaction between the ascending and descending pain system may contribute to the development or maintenance of chronic pain states. Here we provide an overview of the principles, applications, key findings and recent advances of functional imaging in pain research.