Rhinal and hippocampal contributions to spontaneous inter-item binding and verbal memory recall: Evidence from temporal lobe epilepsy

Verbal paired associates learning lateralizes left hippocampal sclerosis in temporal lobe epilepsy

OBJECTIVE

Left hippocampal sclerosis (HS) is associated with verbal-specific memory impairment. This association is well established for word list learning tasks, and there is some evidence that this may also be relevant to verbal paired associates learning (PAL), though the evidence is limited. We aimed to evaluate the utility of verbal PAL as a marker for left HS, compare this with word list learning, and derive cutoff scores to facilitate clinical application.

METHODS

Retrospective analysis of Rey Auditory Verbal Learning Test (RAVLT) and PAL scores obtained from 116 surgically naïve temporal lobe epilepsy patients with HS (14 bilateral, 57 left, 45 right; range of N across test indices: 77-110).

RESULTS

Relative to right HS, left HS and bilateral HS were associated with poorer performance on PAL Hard Pairs (p < 0.001) and all RAVLT indices (p < 0.001), with performance comparable in left HS and bilateral HS (p > 0.05). PAL Hard Pairs and all RAVLT indices displayed acceptable discriminatory ability (AUC > 0.70) in classifying left-sided HS (unilateral left or bilateral HS), with RAVLT delayed recall the strongest predictor (AUC = 0.87; PAL Hard Pairs Learning and Delay = 0.80 and 0.83, respectively). Optimal cutoff scores for left-sided HS classification were generated.

SIGNIFICANCE

Although the RAVLT delayed recall was the strongest predictor of left-sided HS, PAL Hard Pairs also demonstrated excellent discriminatory capacity, offering an additional cognitive marker of left hippocampal integrity to complement word list learning in clinical assessments.

PLAIN LANGUAGE STATEMENT

The results of the study show that the ability to learn unrelated pairs of words (e.g., "silver"-"run") is compromised in the setting of epilepsy with left-sided hippocampal sclerosis (HS), be it unilateral left HS or bilateral HS. The ability of unrelated word pair learning to discriminate left vs. right HS was comparable to word list learning, a task with demonstrated sensitivity to left HS. Our results suggest that the ability to learn unrelated pairs of words provides another useful marker of left-sided hippocampal compromise in epilepsy. We provide cutoff scores to facilitate clinical interpretation.

The modified Ruche visuospatial learning test (RUCHE-M) for the assessment of visuospatial episodic memory in patients with temporal lobe epilepsy: Preliminary evidence for the investigation of memory binding

INTRODUCTION

The Ruche test is a visuospatial form of the Rey auditory verbal learning test (RAVLT), with initial evidence of utility in the diagnosis of temporal lobe epilepsy (TLE)-related memory disorders.

AIMS

To present the translation to Brazilian Portuguese and modification of the Ruche test (RUCHE-M) and compare the RUCHE-M and RAVLT performance between patients with right and left TLE.

METHODS

Twenty-five neuropsychologists participated in instrument adaptation. Thirty-seven patients with right (n = 19) and left (n = 18) TLE participated. Data were compared with the Mann-Whitney U test.

RESULTS

All specialists considered the final RUCHE-M to be adequate. The RUCHE-M forgetting speed index (FSI) score and several RAVLT scores differed significantly between patients with right and left TLE.

CONCLUSION

The RUCHE-M showed limited utility for the assessment of visuospatial episodic memory in patients with TLE. The manipulation of memory binding as demonstrated by FSI score seems to be a promising paradigm for the assessment of right hippocampal function.

Effects of healthy aging and mnemonic strategies on verbal memory performance across the adult lifespan: Mediating role of posterior hippocampus

In this study, we aimed to understand the contributions of hippocampal anteroposterior subregions (head, body, tail) and subfields (cornu ammonis 1-3 [CA1-3], dentate gyrus [DG], and subiculum [Sub]) and encoding strategies to the age-related verbal memory decline. Healthy participants were administered the California Verbal Learning Test-II to evaluate verbal memory performance and encoding strategies and underwent 4.7 T magnetic resonance imaging brain scan with subsequent hippocampal subregions and subfields manual segmentation. While total hippocampal volume was not associated with verbal memory performance, we found the volumes of the posterior hippocampus (body) and Sub showed significant effects on verbal memory performance. Additionally, the age-related volume decline in hippocampal body volume contributed to lower use of semantic clustering, resulting in lower verbal memory performance. The effect of Sub on verbal memory was statistically independent of encoding strategies. While total CA1-3 and DG volumes did not show direct or indirect effects on verbal memory, exploratory analyses with DG and CA1-3 volumes within the hippocampal body subregion suggested an indirect effect of age-related volumetric reduction on verbal memory performance through semantic clustering. As semantic clustering is sensitive to age-related hippocampal volumetric decline but not to the direct effect of age, further investigation of mechanisms supporting semantic clustering can have implications for early detection of cognitive impairments and decline.

Whole-brain functional correlates of memory formation in mesial temporal lobe epilepsy

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Large study of encoding and subsequent memory for words, faces, and scenes.

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Less ipsilateral mesial temporal activity in mesial temporal lobe epilepsy (mTLE).

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Extra-mTL activity in mTLE only partly relevant for memory formation.

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Across materials contralateral mTL decisive to maintain intact memory in mTLE.

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Left frontal activation correlates with better verbal memory only in left mTLE.

The mesial temporal lobe is a key region for episodic memory. Accordingly, memory impairment is frequent in patients with mesial temporal lobe epilepsy. However, the functional relevance of potentially epilepsy-induced reorganisation for memory formation is still not entirely clear. Therefore, we investigated whole-brain functional correlates of verbal and non-verbal memory encoding and subsequent memory formation in 56 (25 right sided) mesial temporal lobe epilepsy patients and 21 controls. We applied an fMRI task of learning scenes, faces, and words followed by an out-of-scanner recognition test. During encoding of faces and scenes left and right mesial temporal lobe epilepsy patients had consistently reduced activation in the epileptogenic mesial temporal lobe compared with controls. Activation increases in patients were apparent in extra-temporal regions, partly associated with subsequent memory formation (left frontal regions and basal ganglia), and patients had less deactivation in regions often linked to the default mode and auditory networks. The more specific subsequent memory contrast indicated only marginal group differences. Correlating patients’ encoding activation with memory performance both within the paradigm and with independent clinical measures demonstrated predominantly increased contralateral mesio-temporal activation supporting intact memory performance. In left temporal lobe epilepsy patients, left frontal activation was also correlated with better verbal memory performance. Taken together, our findings hint towards minor extra-temporal plasticity in mesial temporal lobe epilepsy patients, which is in line with pre-surgical impairment and post-surgical memory decline in many patients. Further, data underscore the importance of particularly the contralateral mesial temporal lobe itself, to maintain intact memory performance.