Abstracts

Rationale: Memory impairment is a common comorbidity within the pediatric epilepsy population. Functional MRI (fMRI) activation of the mesial temporal lobe aids in surgical planning to help minimize post-operative memory decline. The material specificity model of memory proposes the left hippocampus is involved with verbal memory and the right is involved with visual; however, more recent research suggests a more bilateral framework for both verbal and visual memory (Postma et al. 2020, Yoo et al. 2019). While material specific deficits have been observed in children, most pediatric studies do not demonstrate the same material specific deficits seen in adults. Additionally, prior work suggests functional subdivisions along the longitudinal axis of hippocampus. Several theories exist regarding the function of these subdivisions, one posits verbal memory is anterior and visual memory is posterior. Another theory suggests the anterior is involved with encoding and the posterior supports retrieval (HIPER model Lepage et al. 1998). To explore functional organization of the hippocampus in visual memory, we examined amount of activation in visual learning and recognition in children with epilepsy and typically developing (TD) controls.

Methods: A total of 22 patients with focal epilepsy and 17 TD controls (Table 1) completed a paired association visual memory (abstract visual stimuli) fMRI task with both learning and recognition conditions. Image processing was done using SPM 12 and statistical analyses were conducted in SPSS. We extracted amount of activation (magnitude) in anterior and posterior segments of the hippocampus, based on Anatomical Atlas Library from Wake Forest PickAtlas, and calculated lateralization indices (LI). First, we investigated if magnitude of activation varied by hippocampal segment and condition (learning versus recognition).

Results: The visual memory fMRI task activated the hippocampus at an individual level for the majority of subjects and LI (based on magnitude) for all groups was bilateral. For both learning and recognition conditions, we observed increased posterior activation across both patients and controls (p < .001). Additionally, we observed a two-way interaction between hippocampal segment and task condition. The learning condition elicited a greater magnitude of activation in the anterior hippocampus, while the recognition condition produced a greater amount of activation in the posterior hippocampus (p < .001).