28 Challenges to Lateralizing Visual Memory Dysfunction in TLE Patients

Abstract

Objective:

Neuropsychological assessment is an essential part of presurgical evaluation for epilepsy patients with refractory temporal lobe epilepsy. Evaluations assist in localizing and lateralizing epileptogenic focal points and identifying possible risks for cognitive decline following surgery. Researchers and clinicians consistently find that verbal memory dysfunction is an accurate indicator of left temporal lobe epilepsy (TLE) through verbal measures such as the CVLT-II. Although visual memory structures are assumed to be in the right (nondominant) hemisphere, visual memory assessments have not been reliable in identifying right TLE. It is hypothesized that assessments to test visual memory are confounded by verbal cueing to assist in visual learning. To account for this, researchers have identified that comparing verbal and visual score asymmetries does accurately differentiate left and right TLE patients. This study aimed to determine if verbalvisual asymmetry using the CVLT-II and BVMT-R accurately identifies left and right TLE relative weaknesses potentially associated with epileptogenic regions.

Participants and Methods:

As part of a pre-surgical neuropsychological evaluation, 37 well-characterized medically refractory TLE patients (18 right TLE; 19 left TLE) were administered the Brief Visuospatial Memory Test-Revised to evaluate visuospatial memory and the CVLT-II to evaluate verbal memory. A multivariate analysis of variance was used to compare RTLE and LTLE group performances on BVMT-R delay recall subscales, using T-scores. Then memory asymmetry scores were calculated by converting CVLT-II verbal delay memory scores to T-scores and subtracting BVMT-R delayed recall T-score from the verbal memory T-score. An independent samples t-test was used to compare asymmetry scores between the groups.

Results:

There were no significant differences between patients with RTLE and LTLE for BVMT-R Delay [F(2,34) = 0.11, p = .895]. There was not a significant difference when accounting for verbal-visual asymmetry (t (35) = 0.422, p = 0.675, d = 12.566) between left (M = -2.42, SD = 13.82) and right side (M = -4.17, SD = 11.09).

Conclusions:

The BVMT-R did not identify nondominant hemisphere dysfunction in this sample of 18 right TLE patients. Because visual memory performance did not inform lateralization, we investigated the usefulness of memory asymmetry. Inconsistent with our hypothesis, verbal-visual memory asymmetry scores did not differentiate RTLE from LTLE in this sample. These findings add to existing findings that the BVMT-R may not be able to identify visuospatial memory dysfunction in epilepsy. Additionally, these data indicate the inability to assess for visuospatial memory even when accounting for verbal abilities in epilepsy patients. Future research should consider alternate visuospatial measures for the evaluation of epilepsy patients.