Abstracts

Rationale: Memory impairments are a common comorbidity in adults and children with epilepsy; however, few studies have used functional magnetic resonance imaging (fMRI) to assess memory functioning in adults and children with epilepsy. Therefore, we sought to develop a paired association learning fMRI task to directly probe verbal memory and elicit hippocampal activation on an individual basis. We hypothesized that activation would be lateralized and would be related to task memory performance. Methods: We examined hippocampal activation during an EPI BOLD 3T block design task of paired association learning with word pair stimuli. Six blocks were presented with each block consisting of three trials [learning, distraction (baseline), and recall]. Eleven typically developing controls (age range: 11-29 years) and 5 patients with focal epilepsy (age range: 12-52 years) have been piloted on the memory paradigm. Imaging processing and statistical analyses were conducted in SPM8. The region of interest (ROI) for bilateral hippocampi was based on the Anatomical Atlas Library in the Wake Forest PickAtlas. We calculated a laterality index (LI) for the hippocampal ROI using the LI Toolbox. Results: On an individual basis, 91% (10 of 11) of the TD controls and 100% (5 of 5) of the patients demonstrated activation in the hippocampus during the learning trial. During the recall block, 73% (8 of 11) of the TD controls and 80% (4 of 5) of patients demonstrated hippocampal activation (all analyses thresholded at p=0.05, uncorrected). A group map (p=FDR) for the controls rendered a cluster of 13 voxels in the hippocampus for the learning trial, and 292 voxels for the recall trial. The pattern of categorical distribution of laterality was left lateralized for adult controls, particularly during the learning block (adult controls: 7 left, 1 bilateral) and more bilateral for adult patients (2 bilateral). In the pediatric group, both controls and patients with epilepsy showed similar laterality patterns during the learning condition (pediatric controls: 2 left, 1 right; pediatric patients: 2 left, 1 right). Conclusions: The preliminary results demonstrate that this verbal learning paradigm reliably activates the hippocampus on an individual basis. Further, adult controls showed primarily left-lateralized hippocampal activation during the learning block, as expected. We plan to investigate the effect of age, duration of epilepsy, and other clinical variables, as well as task performance on memory activation patterns.