Interoceptive cortex in the posterior insula: comment on Garcia-Larrea et al. 2010 Brain 133, 2528.

Sir, In a recent publication in Brain, Garcia-Larrea et al. (2010) reported their identification of patients with post-stroke central pain and selective thermosensory dysfunction, but without other somatosensory abnormalities, and they suggested that the basis for such dissociated symptoms might be the presence of a 'third somatosensory area' specifically supporting temperature sensation in the operculo-insular region. In actuality, prior findings, which they did not cite, provide solid neurobiological evidence that the dorsal posterior insula contains the primary cortical sensory representation of temperature and pain in humans; indeed, these previous findings explain perfectly well these and other clinical observations by Garcia-Larrea and colleagues. In a carefully designed positron emission tomography study (Craig et al., 2000), my colleagues and I examined cerebral activation associated with six different innocuous cool temperatures applied to the hand of awake human subjects, and by performing a regression analysis against stimulus temperature across scans, we obtained clear and unequivocal evidence that the only site in the Figure 1 Images from a positron emission tomography study showing the localization in the dorsal margin of the posterior insula of the only site in contralateral cortex activated in direct (linear) proportion to the objective temperature of a cooling stimulus (Craig et al., 2000).