Novel analogous tasks to assess material-specific memory impairments associated with temporal lobe epilepsy

Episodic memory tasks employing verbal material are generally sensitive to material-specific memory impairments in individuals with left mesial temporal lobe epilepsy (LTLE), whereas visuospatial memory tasks are less consistently failed by individuals with right mesial temporal lobe epilepsy (RTLE). A limitation of these tasks is the possibility for the examinee to use verbalization strategies when tested with visuospatial stimuli, and visualization strategies with verbal material. In this study, we aimed to develop two new analogous computerized recognition tasks to identify material-specific memory impairments, adapted from those previously developed in our lab: one using verbal material (i.e., pseudowords), and the other visuospatial material (i.e., pictures depicting similar landscapes of mountains, trees, and lakes). Each task consists of a 3-trial learning phase and delayed recognition trials after 30 min. and two weeks. After having established normative data for adults (N = 124), we assessed the ability of each task to detect material-specific memory impairments in patients who have had surgery for LTLE (n = 16) or RTLE (n = 12). Both tasks have good psychometric properties. The RTLE group showed significantly poorer performance on the visuospatial than on the verbal memory test on all trials. The LTLE group showed significantly poorer performance on the verbal than on the visuospatial memory test on delayed (30-min. and 2-week) recognition trials. Memory profile on delayed recognition trials was concordant with the lateralization of epilepsy surgery in 87.5% of LTLE and in 83.3% of the RTLE group. This study provides preliminary clinical validation for our novel tasks to detect material-specific memory impairments in individuals with temporal lobe epilepsy.