Abstracts

Rationale: Memory impairments are a common comorbidity in epilepsy; therefore, functional magnetic resonance imaging (fMRI) to assess memory functioning yields valuable information. However, no published fMRI memory studies exist for children with epilepsy. Therefore, we developed a paired association learning fMRI task to elicit hippocampal and parahippocampal activation (HA, PHA) to assess material specificity (left hippocampus-verbal, right hippocampus-visual) and compared activation in children with focal epilepsy and typically developing (TD) controls. Methods: Twenty-one children with focal epilepsy (mean age=13.5±2.6) and 17 TD controls (mean age=12.7±2.2) participated in two EPI BOLD 3T block design paired association learning tasks: 1) word pair stimuli (verbal memory: n=16 TD; n=17 patients: 9 left focal, 8 right focal) and 2) abstract designs (visual memory: n=16 TD; n=18 patients: 10 left, 8 right). Imaging processing and statistical analyses were conducted in SPM12. Image segmentation and normalization were done using subjects’ high-resolution T1 images with the CAT12 Toolbox in SPM12, then applying those parameters to EPI images. A field map was used to correct distortion. Results were examined at the whole brain level with bspmview at p=0.001, uncorrected, k>10. Results: At the whole brain level, controls showed primarily left-lateralized HA/PHA for verbal memory fMRI and more bilateral HA/PHA for visual memory fMRI on both learning and recall trials. During verbal learning, controls showed greater left HA and fusiform activation than left focal patients; patients showed greater activation in left BA39. Controls showed varied activation, which was outside of the hippocampus, compared to left focal patients during verbal recall (right parietal and occipital) and compared to the right focal group for both verbal learning and recall (learning: left temporal, left occipital, bilateral frontal, bilateral insula, cingulate; recall: right frontal).  On the visual memory task, we did not find group differences in HA/PHA at the whole brain level, but we found many group differences outside of the hippocampus for the left focal group  for visual learning (left>controls: right occipital) and recall (controls>left: bilateral frontal, left>controls: left temporal, right cerebellar) and for the right focal group for visual learning (controls>right: left temporal, right frontal, right occipital/lingual, right insula); there were no group differences for recall.  Conclusions: Group analysis yielded robust HA/PHA during both verbal and visual memory fMRI tasks for controls, even at the whole brain level. For controls, HA/PHA was left-lateralized for verbal and more bilateral for visual memory. Similar to adult findings, left focal pediatric patients show reduced left HA compared to controls during verbal memory fMRI. However, hippocampal-specific changes were not seen during the visual memory task for left focal epilepsy or either verbal or visual task for the right focal group. The results suggest that these fMRI memory tasks can be used to assess material specificity, and are sensitive to differences in HA in epilepsy populations.  In the future, we will examine the effect of task performance, as well as clinical variables on HA/PHA. Funding: This work was supported by NINDS Division of Intramural Research, Susan S. Spencer Clinical Research Training Fellowship [to L.N.S.] and Avery Translational Research Career Development Program Award [through the Clinical and Translational Science Institute at Children's National to L.N.S.].