Somatic sensation and the insular-opercular cortex: relationship to central pain

We report 5 stroke patients with lesions affecting the insula and parietal operculum sparing the postcentral gyrus (somatosensory cortical area SI); 3 had spontaneous central poststroke pain (CPSP) and 2 did not. All were imaged and underwent quantitative sensory threshold tests, though not all modalities were tested in all subjects. Tactile thresholds were unaltered in all. The patients with CPSP exhibited greatly elevated thresholds for mechanical pain (skinfold pinch), sharpness and thermal sensations; the pain-free patients had distinctly lesser elevations of their skinfold pinch and innocuous and noxious thermal thresholds, and no sharpness deficit. It is therefore suggested that, in the case of similar cortical lesions, the presence or absence of spontaneous pain either modifies the thresholds for some innocuous modalities, or that the degree of deficit of some innocuous modalities determines whether or not central pain occurs.