MEMORY TESTS DISTINGUISH BETWEEN PATIENTS WITH FOCAL TEMPORAL AND EXTRATEMPORAL LOBE EPILEPSY

We examined the ability of preoperative memory performance to distingu ish between patients who had been diagnosed as having left (LTLE, n = 31), right (RTLE, n = 37), and extra-(ETLE, n = 17) temporal lobe foca l epilepsy. All patients eventually underwent surgical resections. Ana lyses indicated that the ETLE group performed better than the RTLE gro up on nonverbal memory measures and better than the LTLE group on verb al memory measures. Discriminant function analyses indicated that use of a combination of measures that assess different aspects of memory w ere of significant value in distinguishing between patients with focal TLE and ETLE. This approach, as compared the use of single measures, improved classification rates of all three groups. The best single pre dictor of group membership, an index of verbal learning, yielded a 47% overall correct classification rate, with sensitivities ranging from 25 to 59%, and performed at worse than chance levels in classifying RT LE patients. A multivariate approach, which included an index of verba l and nonverbal learning, incidental nonverbal memory, and consolidati on of organized and rote verbal material, yielded a 65% correct classi fication rate, with sensitivities ranging from 57 to 75%. This compare s favorably with other noninvasive techniques for lateralizing epilept ogenic lesions.