Abstracts

Rationale: The underlying neural substrate for explicit memory functioning in typically developing (TD) adults has been studied, with encoding of information occurring in hippocampal subregions CA2, CA3, and dentate gyrus (DG), and retrieval in the subiculum (Eldridge et al., 2005; Zeineh et al., 2003). Much less is known about these hippocampal subregions in epilepsy. To address this gap, we determined the volume of these subregions in adults with mesial temporal lobe epilepsy (MTLE) and correlated the volumes with memory ability. We hypothesized that ipsilateral hippocampal subregion volumes would be decreased in the left and right MTLE groups. Further, memory ability would correlate with hippocampal volumes, particularly for subregions implicated in memory encoding and retrieval (CA2, CA3, DG, subiculum). Methods: We examined adults with MTLE (n=33; left MTLE=19, right MTLE=14) and TD controls (n=26). The volumes of the hippocampus and hippocampal subregions (CA1, CA2/3, CA4/DG, subiculum) were calculated using an automated segmentation program (FreeSurfer). We corrected hippocampal measurements for total cerebral volume using estimated total intracranial volume. Memory ability was assessed with the Wechsler Memory Scale (WMS-III: Logical Memory, Verbal Paired Associates, Family Picture, and Faces subtests) for a subset of MTLE patients (n=22). We correlated memory ability with hippocampal subregion volumes. Statistical analysis was conducted in SPSS 22.0 (repeated measures ANOVAs, one-way ANOVAs, Pearson r correlations). Results: Estimated total intracranial volume was not different between groups. The left MTLE group demonstrated reduced overall volume of the left hippocampus compared to TD controls (p=0.01). Repeated measures ANOVA revealed a group (left MTLE vs. controls) by left subregion interaction (p<0.001), with smaller left CA1 volume and other larger subregions (left CA2/3, CA4/DG, subiculum) in the left MTLE group compared to controls (p's<0.001). The right MTLE group demonstrated reduced overall volume of the right hippocampus (p<0.001). Repeated measures ANOVA revealed a main effect of group (controls>