Abstract

We aimed to investigate the working memory (WM) and language separate contributions to verbal learning and memory in patients with unilateral drug-resistant temporal lobe epilepsy (drTLE); additionally, we explored the mediating role of WM on the relationship between the number of antiepileptic drugs (AEDs) and short-term verbal memory. We retrospectively enrolled 70 patients with left (LTLE; n = 44) and right (RTLE; n = 26) drTLE. About 40 similar (age and education) healthy controls were used to determine impairments of groups at WM, language (naming and verbal fluency), and verbal learning and memory (five trials list-learning, story memory—immediate recall). To disentangle the effect of learning from the short-term memory, we separately analyzed performances at the first trial, last trial, and delayed-recall list-learning measures, in addition to the total learning capacity (the sum of the five trials). Correlation and regression analyses were used to assess the contribution of potential predictors while controlling for main clinical and demographic variables, and ascertain the mediating role of WM. All patients were impaired at WM and story memory, whereas only LTLE showed language and verbal learning deficits. In RTLE, language was the unique predictor for the most verbal learning performances, whereas WM predicted the results at story memory. In LTLE, WM was the sole predictor for short-term verbal learning (list-learning capacity; trial 1) and mediated the interaction between AED number and the performance at these measures, whereas language predicted the delayed-recall. Finally, WM confounded the performance at short-term memory in both groups, although at different measures. WM is impaired in drTLE and contributes to verbal memory and learning deficits in addition to language, mediating the relationship between AED number and short-term verbal memory in LTLE. Clinicians should consider this overlap when interpreting poor performance at verbal learning and memory in drTLE.

Highlights

  • Patients with temporal lobe epilepsy show heterogeneous cognitive phenotypes, including various deficits in verbal memory and language [1, 2] and in working memory (WM) [3]

  • Pairwise post-hoc comparisons revealed that, compared to controls, both patient groups had impaired WM (LTLE: p = 0.002; RTLE: p < 0.001), but only the List-Learning Trial 1 (LTLE) group was impaired at verbal memory and language measures: learning capacity (p = 0.001), trial 1 (p = 0.003), trial 5 (p < 0.001), delayed-recall (p < 0.001), story memory (p < 0.001), picture naming (p < 0.001), and semantic fluency (p < 0.001), whereas the RTLE group showed only a story memory impairment (p = 0.002)

  • We found no significant correlations between sex, history of traumatic brain injury (TBI) or focal to bilateral tonic-clonic seizures (FBTCS), and verbal memory variables in any patient group, except a moderate correlation between history of febrile convulsion (HFC) and list-learning capacity, trial 1 and delayed-recall in LTLE

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Summary

Introduction

Patients with temporal lobe epilepsy show heterogeneous cognitive phenotypes, including various deficits in verbal memory and language [1, 2] and in working memory (WM) [3]. WM, a dedicated system for short-term active manipulation of the information, serves as a foundation for various cognitive processes, including verbal learning, language comprehension, and production [4, 5]. WM and the short-term verbal memory span concepts significantly overlap [6], they represent distinct entities [7], functionally correlated within a multi-store memory model [8]. WM involves an active organization and manipulation of the stored information and relates to executive functioning [4]

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