Verbal episodic memory in children undergoing temporal lobe epilepsy surgery: a one-year follow-up study

Verbal episodic memory (VEM) is often unimpaired in children with focal epilepsy undergoing left temporal lobe resections, unlike what we might expect in the adult brain. The latter findings suggest that epileptiform activity in early life disrupts memory system lateralization, leading to the development of bilateral memory representation. The present study aims to analyze whether the laterality of epilepsy is a major predictor for post-operative VEM prognosis in pediatric temporal lobe epilepsy (TLE) surgery. This research also pretends to provide evidence about the relationship of VEM performance with other relevant demographical and clinical factors such as sex, age at onset of seizures, age at surgery and duration of epilepsy, as well as to study the impact of presurgical VEM performance on postsurgical outcomes.

Pre-operative and one-year follow-up post-operative word-list recall scores from 25 children who underwent TLE surgery (left-sided, n = 11; right-sided, n = 14) were extracted from the Hospital Sant Joan de Deu database and were retrospectively analyzed.

No significant presurgical intergroup differences were found when comparing VEM scores by laterality of epilepsy (p > 0.5). Looking at the left TLE group, a high negative correlation was found between the onset age and the pre-operative long-term free recall score (rho = -0.72, p = 0.01). No significant pre- to post-operative intragroup changes were found regarding VEM performance, regardless of epilepsy laterality (left TLE group, p > 0.56; right TLE group, p > 0.12).

The laterality of epilepsy does not show to be a significant factor in and of itself regarding presurgical VEM outcome and its prognosis one year after surgery, thus supporting the bilateral memory representation hypothesis. Furthermore, a younger age at onset of seizures seems to be related with a better pre-operative VEM performance, likely due to a more efficient reorganization of memory system induced by a greater brain plasticity at lower ages; however, this relationship has been only reported for the left-sided epilepsies in our sample.