Abstracts

Rationale: A deficit in declarative memory function is common among individuals with temporal lobe epilepsy. Studies using MRI have shown that hippocampal atrophy in this population is directly related to poor performance on memory tests. However, less is known about how structures surrounding the hippocampus contribute to this memory dysfunction. Of particular interest are the white matter pathways that supply the hippocampus with multi-modal sensory information. Degradation of these pathways may disrupt the transfer of information important for the formation of new memory. The purpose of this study is to evaluate the relationship between the volume of the hippocampus along with the surrounding white matter and memory performance in those with temporal lobe epilepsy.Methods: T1 weighted MRI scans were acquired using a 3-D SPGR pulse sequence in 50 right handed individuals with temporal lobe epilepsy. Hippocampal volumes were derived by manually tracing consecutive coronal slices aligned perpendicular to the long axis of the hippocampus. In addition, parahippocampal white matter volumes were determined using voxel based morphometry and statistical parametric mapping (SPM2). Finally, declarative memory was assessed using immediate and delayed verbal and visual memory tests from the Wechsler Memory Scale third edition.Results: Of the 50 individuals with temporal lobe epilepsy 12 had left hippocampal atrophy, 11 had right hippocampal atrophy and 27 had no hippocampal atrophy. Significant correlations were seen between right and left hippocampal volumes and delayed verbal memory test scores (R=0.323, p=0.022 and R=0.30, p=0.0346 respectively). In addition, left parahippocampal white matter showed positive correlations with immediate verbal and visual as well as delayed verbal and visual memory scores (R=0.31, p=0.0286; R=0.381, p=0.006; R=0.29, p=0.04 and R=0.31, p=0.0282 respectively).Conclusions: These results show that in addition to hippocampal atrophy, a decrease in white matter fibers projecting to the hippocampus may cause a disruption of incoming multi-modal sensory information. Therefore, the loss of white matter along with hippocampal atrophy may contribute to the declarative memory decline seen in subjects with temporal lobe epilepsy.