Noninvasive cortical modulation of experimental pain.

Noninvasive cortical stimulation (NICS) can produce analgesic effects by means of repetitive transcranial magnetic stimulation or transcranial direct current stimulation (tDCS). Such effects have been demonstrated on chronic ongoing pain, as in acute provoked pain. The investigation of induced changes in the perception of experimental pain by NICS could help clinicians and researchers to better understand the mechanisms of action involved with these techniques and the role played by the cortex in the integration of nociceptive information. This review presents current literature data on the modulation of experimental pain perception by cortical stimulation. The observations found that NICS analgesic effects depend on the method used to provoke pain (referring to the type of nerve fibers and neural circuits that are recruited to mediate pain) and the parameters of cortical stimulation (especially the nature of the cortical target). The motor cortex (precentral cortical area) is the most widely used target for pain modulation. However, other targets, such as the dorsolateral prefrontal cortex, could be of particular interest to modulate various components of pain. Further developments in NICS techniques, such as image-guided navigated brain stimulation, might lead to improvement in the beneficial effects of NICS on pain. Finally, we discuss whether the results obtained in experimental pain can be transposed to the problem of chronic pain and whether they can be used to optimize cortical stimulation therapy for pain disorders.