Imaging episodic memory during development and childhood epilepsy

Abstract

Epilepsy affects 2.2 million adults in the USA, with 1 in 26 people developing epilepsy at some point in their lives. Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy as medial structures, and the hippocampus in particular, are prone to generating seizures. Selective anterior temporal resection (which removes the hippocampus) is the most effective intractable TLE treatment, but given the critical role of the mesial temporal lobe in memory functioning, resection can have negative effects on this crucial cognitive skill. To minimize the adverse impact of temporal lobe surgery on memory functioning, reliable pre-surgical guides are needed. Clinical functional magnetic resonance imaging (fMRI) provides reliable, noninvasive guidance of language functioning and plays a growing role in the pre-surgical evaluation for epilepsy patients; however, localization of memory function in children with epilepsy using fMRI has not been established. Aside from the lack of neuroimaging memory studies in children with TLE, studies of typical development are limited. This review will focus on the functional anatomy of memory systems throughout development, with a focus on TLE. TLE provides the ideal model from which to understand memory function and the limits of plasticity and compensation/reorganization throughout development.

Fig. 1

Results from hippocampal region of interest, comparing correct R and correct K response amplitudes (a). Event-related responses within the left hippocampal region; response amplitude for correct R trials was greater than that for correct K trials (b). Adapted with permission from Eldridge et al. [40]

Fig. 2

Activation in MTL for two participants. Pattern encoding yielded right, word yielded left, and face and scene encoding yielded bilateral activation. Adapted with permission from Golby et al. [96]

Fig. 3

During language fMRI, the peak MTL voxel is depicted for each individual in the adult and pediatric age group (blue represents TD controls and green represents epilepsy). MTL was more left lateralized in adults than children. MTL, mesial temporal lobe. Adapted with permission from Sepeta et al. [71]