Pain sensitivity alterations as a function of lesion location in the parasylvian cortex

Six patients with lesions involving parasylvian cerebral cortex were evalua ted for their pain thresholds using contact heat (all six) and sharp probes that evoke pin-prick pain (4/6). Without knowledge of the sensory status o f the individuals, two of the authors evaluated the MRIs of these patients, and determined to what extent the following cerebral regions were involved in the lesion: anterior insula, posterior insula, retroinsula, and parieta l operculum. Each patient's lesion encompassed at least two of these region s. Three individuals demonstrated significant laterality differences in pai n sensitivity, with elevated thresholds on the hand contralateral to his/he r lesion. The common feature in these cases was the inclusion of the pariet al operculum and posterior insula. The three other cases showed no evidence of abnormal pain thresholds. The common feature of these cases was the app arent sparing of the parietal operculum. Thus, this series of cases points to the significance of the parietal operculum, either alone or with adjacen t posterior insula, for normal pain thresholds. In comparison, extensive in volvement of the anterior insula in two cases was not associated with abnor mal pain thresholds. Four of the six patients were also evaluated with a co ld pain tolerance test, which presumably involves more affective/motivation al aspects of pain than threshold tests. Only two of these patients showed greater tolerance contralaterally versus ipsilaterally, and theirs were the two lesions of the four with involvement of a large part of the insula. Th is result supports the theory that the insula's involvement in nociceptive processing is related to the affective/motivational aspect of pain. (C) 199 9 International Association for the Study of Pain. Published by Elsevier Sc ience B.V.