Insights gained into pain processing from patients with focal brain lesions.

The recognition that dissociated sensory loss affecting selectively pain and temperature results from lesions of the operculo-insular cortex is due to Biemond in 1956. This contrasted with the prevailing view that the sensory aspects of pain did not imply regions above the thalamus. Anatomical data in non-human primates, as well as electrophysiology and functional imaging in humans have now abundantly demonstrated that the opercular-insular region is the main cortical target of the spinothalamic system, and a vast number of reports have confirmed the relation between lesions in this region and the development of dissociated sensory symptoms and central neuropathic pain. Operculo-insular pain (parasylvian pain) is a distinct entity that can be clinically suspected and objectively diagnosed with combined radiological and electrophysiological methods, in particular evoked potentials to spinothalamic (laser) input. The region comprising the posterior insula and medial operculum may deserve being considered as a third somatosensory cortex (S3) contributing to the spinothalamic attributes of somatic perception.