Abstracts

Rationale: Memory impairments are a common comorbidity in adults with epilepsy; therefore, functional magnetic resonance imaging (fMRI) to assess memory functioning yields valuable information regarding a commonly affected area of cognitive functioning in epilepsy. We used a verbal fMRI memory paradigm to compare mesial temporal lobe (MTL) activation in adults with focal epilepsy (EPI) and typically developing (TD) controls. Methods: Sixteen patients referred to the Clinical Epilepsy Section at the National Institute of Neurological Disease and Stroke (NINDS), National Institutes of Health (NIH) for presurgical evaluation of drug-resistant epilepsy and 16 TD controls (TD mean age: 30.7 years; EPI mean age: 36.3 years) completed an EPI BOLD 3T verbal memory block design task. The task consisted of paired association learning with word stimuli. Six blocks were presented with each block consisting of three trial types [learning, distraction (baseline), and recall]. Imaging processing and statistical analyses were conducted in SPM12. Image normalization and segmentation was done using subjects' high-resolution T1 images with the CAT12 Toolbox in SPM12, then applying those parameters to EPI images. A field map was acquired and used to correct distortion. MTL region of interest (ROI) included hippocampi and parahippocampal gyri based on the Anatomical Atlas Library in the Wake Forest PickAtlas. The MTL was chosen as a specific ROI because it has a particular role in episodic memory encoding and retrieval. We calculated a bootstrapped MTL ROI lateralization index (LI) using the LI Toolbox. Results: Controls showed left-lateralized MTL activation for both learning and recall trials (p=0.05, FDR; k>5: learning> baseline LI=0.62; recall>baseline LI=0.8). Patients demonstrated right-lateralized activation for the learning trial and bilateral MTL activation for the recall trial (p=0.05, FDR; k>5; learning>baseline LI=-0.5; recall>baseline LI=-0.06). For both the learning and recall trials group comparisons (TD>EPI; EPI>TD), controls showed greater activation in the left MTL than patients, and patients showed greater right activation (p=0.05, uncorrected, k=5). Conclusions: Group analysis of this verbal memory paradigm yielded left-lateralized MTL activation for controls during encoding and retrieval. In contrast, group analysis of patients, showed right-lateralized MTL activation during encoding and bilateral MTL activation for retrieval. When patients and controls were directly compared, the patients with focal epilepsy demonstrated more right lateralized MTL activation for both the learning and recall trials, compatible with an affected network for memory recall in the patients. We are currently adding additional study participants in order to look at the effect of focus on activation maps, as well as analyzing results on an individual basis which will be important for establishing clinical utility. 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.].