Abstracts

RATIONALE: To examine relationships between verbal memory and glucose metabolism in mesial and lateral temporal lobes of patients with temporal lobe epilepsy (TLE). METHODS: Sixteen patients with focal TLE underwent preoperative FDG-PET. Absolute counts for lateral temporal neocortex were obtained from four axial planes ranging from posterior superior temporal lobe to the temporal pole. The hippocampus was outlined by hand. Asymmetry indices were also calculated. All values were normalized by global cerebral metabolism. Verbal memory was assessed using the the Logical Memory delayed score (LM II) and the Logical Memory savings score (LM %) from the Wechsler Memory Scale. Only correlations achieving at least 80% power at p < .05 were considered significant (r ?.55). RESULTS: Both verbal memory measures correlated directly and significantly with the hippocampal asymmetry index (LMII = .77, LM% = .60). Both measures were also strongly related to the asymmetry indices from each plane in the lateral temporal lobe, with correlations ranging from .55 to .82. Examination of correlations with left and right values revealed an interesting pattern; verbal memory was directly related to left mesial and lateral temporal values, but inversely related to right values. CONCLUSIONS: Temporal lobe metabolic asymmetry strongly predicts verbal memory performance in patients with TLE. These findings are consistent with recent studies demonstrating ipsilateral hypometabolism and contralateral hypermetabolism in patients with TLE. In this context, our paradoxical finding of an inverse relationship between verbal memory and right temporal metabolism probably reflects the unique spatial distribution of local and distal metabolic changes in patients with intractable, focal TLE. Finally, our findings suggest that episodic verbal memory may be related equally to the mesial and lateral temporal lobes, suggesting that the left temporal lobe memory network is distributed rather than localized. Combined with the recent evidence of postoperative metabolic normalization, these finding may help explain reports of actual improvement in verbal memory following left temporal lobectomy.