On the origin of painful somatosensory seizures

Objective: To explore whether painful somatosensory seizures (PSS) are generated in the primary somatosensory cortex (SI area) or in the operculo-insular cortex. Methods: We analyzed ictal recordings and data from stimulation using intracerebral electrodes exploring the operculo-insular cortex (including secondary somatosensory [SII] region), SI area, and other areas of the pain matrix (cingulate gyrus and supplementary motor area) in a case series study of 5 patients with PSS. Results: Clinical features of PSS were different from those of seizures arising from the SI area: (1) pain intensity was higher; (2) pain spreading was not from one somatotopic territory to adjacent ones; and (3) the spatial extent of pain was large, fitting better with the size of somatosensory receptive fields of the insula and SII region than of the SI area. The insula and SII region were systematically involved at the onset of seizures, rapidly followed by the opercular portion of SI area. The upper part of SI cortex was involved at a lesser degree, with some delay, and pain duration did not correlate in time with that of the discharge in SI. Ictal pain was consistently reproduced by stimulation of the insula or SII region but never by stimulating the SI area. Conclusions: These data strongly suggest that PSS originate in the operculo-insular cortex and not in the SI area and corroborate the concept that this region is involved in the sensory-discriminative processing of pain inputs. Pain at the onset of PSS has a high value for localizing the epileptogenic area.