Abstracts

Rationale: Based on intracarotid amobarbital procedure (IAP) in post-temporal lobectomy patients, we recently reported that the IAP memory scores, when considered in the context of hippocampal memory dominance, correlated well with postoperative neuropsychological evaluation (NPE) (Burton et al, Epilepsia 2007 online early). In this study, we investigated whether preoperative hippocampal memory dominance on IAP correlated with performance on NPE.Methods: Based on retrospective review, we included patients meeting 3 criteria: left hemisphere dominance for language, clear unilateral memory dominance and well-determined seizure onset by video-EEG monitoring. Patients with bilateral memory representation were excluded. Hippocampal memory dominance was determined from the IAP such that left hippocampal memory dominance was defined by significant memory disruption upon left hemisphere injection and little or no change in functional memory upon right hemisphere injection, and vice versa. Patients with left hippocampal memory dominance (ipsilateral to language-dominant hemisphere) were considered to have dominant hippocampus while patients with right hippocampal memory dominance were considered to have nondominant hippocampus. We analyzed the effects of hippocampal memory dominance (dominant vs. nondominant hippocampus), seizure localization (temporal vs. extra-temporal) and seizure lateralization (left vs. right hemisphere) on interpolated global delay recall scores (from the WMS-R) on NPE using univariate analysis of variance.Results: There were 38 patients in the study (22 female, 16 male, mean age 32 years). The patients in different subgroups was as follows: dominant hippocampus (n=25); nondominant hippocampus (n=13); temporal seizure onset (n=26); extra-temporal seizure onset (n=12); left hemispheric seizure onset (n=18); right hemispheric seizure onset (n=20). Dominant hippocampus patients showed significantly higher global delay recall scores on NPE than nondominant hippocampus patients (93 vs. 78, F=5.315, p=0.028). Overall, neither seizure localization (p=0.263) nor seizure lateralization (p=0.182) significantly affected the NPE scores. Assuming that right temporal seizure onset could have contributed to the lower score in the nondominant hippocampus group, we analyzed the effects of seizure localization and lateralization specifically in this group, and found no significant interactions (p=0.288, p=0.212).Conclusions: Patients with dominant hippocampus (hippocampal memory dominance ipsilateral to language-dominant hemisphere) perform significantly better on NPE as measured by global delay recall scores than patients with nondominant hippocampus (hippocampal memory dominance contralateral to language-dominant hemisphere), regardless of their seizure localization or lateralization. This finding supports the notion of close intra-hemispheric linkage between language and memory which is relevant in considering temporal resection. It also suggests that the nondominant hippocampus can support memory function although not at the level of the dominant hippocampus.