Verbal memory in mesial temporal lobe epilepsy: beyond material specificity

Association of Normative and Non-Normative Brain Networks With Cognitive Function in Patients With Temporal Lobe Epilepsy

BACKGROUND AND OBJECTIVES

Despite their temporal lobe pathology, a significant subgroup of patients with temporal lobe epilepsy (TLE) is able to maintain normative cognitive functioning. In this study, we identify patients with TLE with intact vs impaired neurocognitive profiles and interrogate for the presence of both normative and highly individual intrinsic connectivity networks (ICNs)-all toward understanding the transition from impaired to intact neurocognitive status.

METHODS

This retrospective cross-sectional study included patients with TLE and matched healthy controls (HCs) from the Thomas Jefferson Comprehensive Epilepsy Center. Functional MRI data were decomposed using independent component analysis to obtain individualized ICNs. In this article, we calculated the degree of match between individualized ICNs and canonical ICNs (e.g., 17 resting-state networks by Yeo et al.) and divided each participant's ICNs into normative or non-normative status based on the degree of match.

RESULTS

100 patients with TLE (mean age 42.0 [SD: 13.7] years, 47 women) and 92 HCs were included in this study. We found that the individualized networks matched to the canonical networks less well in the cognitively impaired (n = 24) compared with the cognitively intact (n = 63) patients with TLE by 2-way mixed-measures analysis of variance (impaired vs intact mean difference [MD] -0.165 [-0.317, -0.013], p = 0.028). The cognitively impaired patients showed significant abnormalities in the profiles of both normative (impaired vs intact MD -0.537 [-0.998, -0.076], p = 0.017, intact vs HC MD -0.221 [-0.536, 0.924], p = 0.220, and impaired vs HC MD -0.759 [-1.200, -0.319], p < 0.001) and non-normative networks (impaired vs intact MD 0.484 [0.030, 0.937], p = 0.033, intact vs HC MD 0.369 [0.059, 0.678], p = 0.014, and impaired vs HC MD 0.853 [0.419, 1.286], p < 0.001) while the intact patients showed abnormalities only in non-normative networks. At the same time, we found that normative networks held a strong, positive association with the neuropsychological measures, with this association negative in non-normative networks.

DISCUSSION

Our data demonstrated that significant cognitive deficits are associated with the status of both canonical and highly individual ICNs, making clear that the transition from intact to impaired cognitive status is not simply the result of disruption to normative brain networks.

Does epilepsy differentially affect different types of memory?

Despite the recognition that epilepsy can substantially disrupt memory, there are few published accounts of whether and how this disruption varies across different types of memory and/or different types of epilepsy. This review explores four main questions: (1) Are working, episodic and semantic memory differentially affected by epilepsy? (2) Do various types of epilepsy, and their treatment, have different, specifiable effects on memory? (3) Are the usual forms of neuropsychological assessments of memory - many or most designed for other conditions - appropriate for patients with epilepsy? (4) How can research on epilepsy contribute to our understanding of the neuroscience of memory? We conclude that widespread and multifactorial problems are seen in working memory in all patient groups, while patients with temporal lobe epilepsy seem particularly prone to episodic memory deficit, and those with frontal lobe epilepsy to executive function deficits that may in turn impair semantic control. Currently, it is difficult to make individual patient predictions about likely memory deficits based on seizure aetiology and type, but it is possible to guide and tailor neuropsychological assessments in an individualised way. We make recommendations for future directions in validating and optimising neuropsychological assessments, and consider how to approach effective shared decision making about the pros and cons of seizure treatment strategies, especially at crucial educational stages such as adolescence.

Altered structural network in temporal lobe epilepsy with focal to bilateral tonic-clonic seizures

OBJECTIVES

This study aims to investigate whether alterations in white matter topological networks are associated with focal to bilateral tonic-clonic seizures (FBTCS) in temporal lobe epilepsy (TLE). Additionally, we investigated the variables contributing to memory impairment in TLE.

METHODS

This cross-sectional study included 88 unilateral people with TLE (45 left/43 right), and 42 healthy controls. Graph theory analysis was employed to compare the FBTCS (+) group (n = 51) with the FBTCS (-) group (n = 37). The FBTCS (+) group was subcategorized into current-FBTCS (n = 31) and remote-FBTCS (n = 20), based on the history of FBTCS within 1 year or longer than 1 year before scanning, respectively. We evaluated the discriminatory power of topological network properties by receiver operating characteristic (ROC) analysis. Generalized linear models (GLMs) were employed to investigate variables associated with memory impairment in TLE.

RESULTS

Global efficiency (Eg) was significantly reduced in the FBTCS (+) group, especially in the current-FBTCS subgroup. Greater disruption of regional properties in the ipsilateral occipital and temporal association cortices was observed in the FBTCS (+) group. ROC analysis revealed that Eg, normalized characteristic shortest path length, and nodal efficiency of the ipsilateral middle temporal gyrus could distinguish between FBTCS (+) and FBTCS (-) groups. Additionally, GLMs linked the occurrence of current FBTCS with poorer verbal memory outcomes in TLE.

INTERPRETATION

Our study suggests that abnormal networks could be the structural basis of seizure propagation in FBTCS. Strategies aimed at reducing the occurrence of FBTCS could potentially improve the memory outcomes in people with TLE.

Sex differences in the pre and postoperative neuropsychological function of epilepsy surgery candidates

Objective: As programs expand globally, epilepsy surgery is becoming increasingly available as an effective treatment for some people with medically intractable seizures. Prospective candidates require careful neuropsychological evaluation and follow-up. The aim of this study was to examine the sex differences in neuropsychological function in presurgical presentation and postoperative outcomes in people with temporal lobe epilepsy referred for epilepsy surgery. Methods: Three hundred and seventy-two patients (202 Female; 170 Male) with a homogenous underlying pathology (hippocampal sclerosis) underwent a preoperative assessment on tests of intellectual, language, and memory function and were followed up one year after undergoing a unilateral temporal lobe resection; n = 169 Right (RTL), n = 203 Left (LTL). Results: There was no impact of sex or laterality of surgery on seizure outcome; 84% of males and 80% of females were seizure free at follow-up. Before surgery, sex effects were evident on tests of verbal memory with females performing better than males. Declines in verbal memory function following surgery were greater in females than males. Being female had a stronger association with postoperative decline on immediate prose recall (partial eta squared η2 = 0.029), than side of surgery (η2 = 0.018) albeit with a small effect size. Conclusions: There are subtle but significant sex differences in the neuropsychological profiles of people with temporal lobe epilepsy, before and following surgery. Whilst females generally perform better than males on tests of verbal memory function before surgery they demonstrate greater post-operative declines on these measures following surgery.

Cross-cultural application of the International Classification of Cognitive Disorders in Epilepsy (IC-CoDE): Cognitive phenotypes in people with temporal lobe epilepsy in India

OBJECTIVE

Efforts to understand the global variability in cognitive profiles in patients with epilepsy have been stymied by the lack of a standardized diagnostic system. This study examined the cross-cultural applicability of the International Classification of Cognitive Disorders in Epilepsy (IC-CoDE) in a cohort of patients with temporal lobe epilepsy (TLE) in India that was diverse in language, education, and cultural background.

METHODS

A cohort of 548 adults with TLE from Mumbai completed a presurgical comprehensive neuropsychological evaluation. The IC-CoDE taxonomy was applied to derive cognitive phenotypes in the sample. Analyses of variance were conducted to examine differences in demographic and clinical characteristics across the phenotypes, and chi-squared tests were used to determine whether the phenotype distribution differed between the Mumbai sample and published data from a multicenter US sample.

RESULTS

Using the IC-CoDE criteria, 47% of our cohort showed an intact cognitive profile, 31% a single-domain impairment, 16% a bidomain impairment, and 6% a generalized impairment profile. The distribution of cognitive phenotypes was similar between the Indian and US cohorts for the intact and bidomain phenotypes, but differed for the single and generalized domains. There was a larger proportion of patients with single-domain impairment in the Indian cohort and a larger proportion with generalized impairment in the US cohort. Among patients with single-domain impairment, a greater proportion exhibited memory impairment in the Indian cohort, whereas a greater proportion showed language impairment in the US sample, likely reflecting differences in language administration procedures and sample characteristics including a higher rate of mesial temporal sclerosis in the Indian sample.

SIGNIFICANCE

Our results demonstrate the applicability of IC-CoDE in a group of culturally and linguistically diverse patients from India. This approach enhances our understanding of cognitive variability across cultures and enables harmonized and inclusive research into the neuropsychological aspects of epilepsy.

The network is more important than the node: stereo-EEG evidence of neurocognitive networks in epilepsy

Introduction

Neuropsychological assessment forms an integral part of the presurgical evaluation for patients with medically refractory focal epilepsy. Our understanding of cognitive impairment in epilepsy is based on seminal lesional studies that have demonstrated important structure-function relationships within the brain. However, a growing body of literature demonstrating heterogeneity in the cognitive profiles of patients with focal epilepsy (e.g., temporal lobe epilepsy; TLE) has led researchers to speculate that cognition may be impacted by regions outside the seizure onset zone, such as those involved in the interictal or "irritative" network.

Methods

Neuropsychological data from 48 patients who underwent stereoelectroencephalography (SEEG) monitoring between 2012 and 2023 were reviewed. Patients were categorized based on the site of seizure onset, as well as their irritative network, to determine the impact of wider network activity on cognition. Neuropsychological data were compared with normative standards (i.e., z = 0), and between groups.

Results

There were very few distinguishing cognitive features between patients when categorized based purely on the seizure onset zone (i.e., frontal lobe vs. temporal lobe epilepsy). In contrast, patients with localized irritative networks (i.e., frontal or temporal interictal epileptiform discharges [IEDs]) demonstrated more circumscribed profiles of impairment compared with those demonstrating wider irritative networks (i.e., frontotemporal IEDs). Furthermore, the directionality of propagation within the irritative network was found to influence the manifestations of cognitive impairment.

Discussion

The findings suggest that neuropsychological assessment is sensitive to network activity beyond the site of seizure onset. As such, an overly focal interpretation may not accurately reflect the distribution of the underlying pathology. This has important implications for presurgical work-up in epilepsy, as well as subsequent surgical outcomes.

Excitation/Inhibition balance relates to cognitive function and gene expression in temporal lobe epilepsy: a high density EEG assessment with aperiodic exponent

Patients with epilepsy are characterized by a dysregulation of excitation/inhibition balance (E/I). The assessment of E/I may inform clinicians during the diagnosis and therapy management, even though it is rarely performed. An accessible measure of the E/I of the brain represents a clinically relevant feature. Here, we exploited the exponent of the aperiodic component of the power spectrum of the electroencephalography (EEG) signal, as a non-invasive and cost-effective proxy of the E/I balance. We recorded resting-state activity with high-density EEG from 67 patients with temporal lobe epilepsy and 35 controls. We extracted the exponent of the aperiodic fit of the power spectrum from source-reconstructed EEG and tested differences between patients with epilepsy and controls. Spearman's correlation was performed between the exponent and clinical variables (age of onset, epilepsy duration and neuropsychology) and cortical expression of epilepsy-related genes derived from the Allen Human Brain Atlas. Patients with temporal lobe epilepsy showed a significantly larger exponent, corresponding to inhibition-directed E/I balance, in bilateral frontal and temporal regions. Lower E/I in the left entorhinal and bilateral dorsolateral prefrontal cortices corresponded to a lower performance of short-term verbal memory. Limited to patients with temporal lobe epilepsy, we detected a significant correlation between the exponent and the cortical expression of GABRA1, GRIN2A, GABRD, GABRG2, KCNA2 and PDYN genes. EEG aperiodic exponent maps the E/I balance non-invasively in patients with epilepsy and reveals a close relationship between altered E/I patterns, cognition and genetics.

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.

Impact of white matter networks on risk for memory decline following resection versus ablation in temporal lobe epilepsy

BACKGROUND

With expanding neurosurgical options in epilepsy, it is important to characterise each options' risk for postoperative cognitive decline. Here, we characterise how patients' preoperative white matter (WM) networks relates to postoperative memory changes following different epilepsy surgeries.

METHODS

Eighty-nine patients with temporal lobe epilepsy with T1-weighted and diffusion-weighted imaging as well as preoperative and postoperative verbal memory scores (prose recall) underwent either anterior temporal lobectomy (ATL: n=38) or stereotactic laser amygdalohippocampotomy (SLAH; n=51). We computed laterality indices (ie, asymmetry) for volume of the hippocampus and fractional anisotropy (FA) of two deep WM tracts (uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF)).

RESULTS

Preoperatively, left-lateralised FA of the ILF was associated with higher prose recall (p<0.01). This pattern was not observed for the UF or hippocampus (ps>0.05). Postoperatively, right-lateralised FA of the UF was associated with less decline following left ATL (p<0.05) but not left SLAH (p>0.05), while right-lateralised hippocampal asymmetry was associated with less decline following both left ATL and SLAH (ps<0.05). After accounting for preoperative memory score, age of onset and hippocampal asymmetry, the association between UF and memory decline in left ATL remained significant (p<0.01).

CONCLUSIONS

Asymmetry of the hippocampus is an important predictor of risk for memory decline following both surgeries. However, asymmetry of UF integrity, which is only severed during ATL, is an important predictor of memory decline after ATL only. As surgical procedures and pre-surgical mapping evolve, understanding the role of frontal-temporal WM in memory networks could help to guide more targeted surgical approaches to mitigate cognitive decline.

Evidence for interictal blood-brain barrier dysfunction in people with epilepsy

OBJECTIVE

Interictal blood-brain barrier dysfunction in chronic epilepsy has been demonstrated in animal models and pathological specimens. Ictal blood-brain barrier dysfunction has been shown in humans in vivo using an experimental quantitative magnetic resonance imaging (MRI) protocol. Here, we hypothesized that interictal blood-brain barrier dysfunction is also present in people with drug-resistant epilepsy.

METHODS

Thirty-nine people (21 females, mean age at MRI ± SD = 30 ± 8 years) with drug-resistant epilepsy were prospectively recruited and underwent interictal T1-relaxometry before and after administration of a paramagnetic contrast agent. Likewise, quantitative T1 was acquired in 29 people without epilepsy (12 females, age at MRI = 48 ± 18 years). Quantitative T1 difference maps were calculated and served as a surrogate imaging marker for blood-brain barrier dysfunction. Values of quantitative T1 difference maps inside hemispheres ipsilateral to the presumed seizure onset zone were then compared, on a voxelwise level and within presumed seizure onset zones, to the contralateral side of people with epilepsy and to people without epilepsy.

RESULTS

Compared to the contralateral side, ipsilateral T1 difference values were significantly higher in white matter (corrected p < .05), gray matter (uncorrected p < .05), and presumed seizure onset zones (p = .04) in people with epilepsy. Compared to people without epilepsy, significantly higher T1 difference values were found in the anatomical vicinity of presumed seizure onset zones (p = .004). A subgroup of people with hippocampal sclerosis demonstrated significantly higher T1 difference values in the ipsilateral hippocampus and in regions strongly interconnected with the hippocampus compared to people without epilepsy (corrected p < .01). Finally, z-scores reflecting the deviation of T1 difference values within the presumed seizure onset zone were associated with verbal memory performance (p = .02) in people with temporal lobe epilepsy.

SIGNIFICANCE

Our results indicate a blood-brain barrier dysfunction in drug-resistant epilepsy that is detectable interictally in vivo, anatomically related to the presumed seizure onset zone, and associated with cognitive deficits.

Verbal memory network mapping in individual patients predicts postoperative functional impairments

Verbal memory decline is a significant concern following temporal lobe surgeries in patients with epilepsy, emphasizing the need for precision presurgical verbal memory mapping to optimize functional outcomes. However, the inter-individual variability in functional networks and brain function-structural dissociations pose challenges when relying solely on group-level atlases or anatomical landmarks for surgical guidance. Here, we aimed to develop and validate a personalized functional mapping technique for verbal memory using precision resting-state functional MRI (rs-fMRI) and neurosurgery. A total of 38 patients with refractory epilepsy scheduled for surgical interventions were enrolled and 28 patients were analyzed in the study. Baseline 30-min rs-fMRI scanning, verbal memory and language assessments were collected for each patient before surgery. Personalized verbal memory networks (PVMN) were delineated based on preoperative rs-fMRI data for each patient. The accuracy of PVMN was assessed by comparing post-operative functional impairments and the overlapping extent between PVMN and surgical lesions. A total of 14 out of 28 patients experienced clinically meaningful declines in verbal memory after surgery. The personalized network and the group-level atlas exhibited 100% and 75.0% accuracy in predicting postoperative verbal memory declines, respectively. Moreover, six patients with extra-temporal lesions that overlapped with PVMN showed selective impairments in verbal memory. Furthermore, the lesioned ratio of the personalized network rather than the group-level atlas was significantly correlated with postoperative declines in verbal memory (personalized networks: r = -0.39, p = .038; group-level atlas: r = -0.19, p = .332). In conclusion, our personalized functional mapping technique, using precision rs-fMRI, offers valuable insights into individual variability in the verbal memory network and holds promise in precision verbal memory network mapping in individuals.

Unilateral hippocampal sparing during whole brain radiotherapy for multiple brain metastases: narrative and critical review

Background

The landscape of brain metastases radiotherapy is evolving, with a shift away from whole-brain radiotherapy (WBRT) toward targeted stereotactic approaches aimed at preserving neurocognitive functions and maintaining overall quality of life. For patients with multiple metastases, especially in cases where targeted radiotherapy is no longer feasible due to widespread dissemination, the concept of hippocampal sparing radiotherapy (HA_WBRT) gains prominence.

Methods

In this narrative review we explore the role of the hippocampi in memory formation and the implications of their postradiotherapy lateral damage. We also consider the potential advantages of selectively sparing one hippocampus during whole-brain radiotherapy (WBRT). Additionally, by systematic evaluation of relevant papers published on PubMed database over last 20 years, we provide a comprehensive overview of the various changes that can occur in the left or right hippocampus as a consequence of radiotherapy.

Results

While it is important to note that various neurocognitive functions are interconnected throughout the brain, we can discern certain specialized roles of the hippocampi. The left hippocampus appears to play a predominant role in verbal memory, whereas the right hippocampus is associated more with visuospatial memory. Additionally, the anterior part of the hippocampus is more involved in episodic memory and emotional processing, while the posterior part is primarily responsible for spatial memory and pattern separation. Notably, a substantial body of evidence demonstrates a significant correlation between post-radiotherapy changes in the left hippocampus and subsequent cognitive decline in patients.

Conclusion

In the context of individualized palliative radiotherapy, sparing the unilateral (specifically, the left, which is dominant in most individuals) hippocampus could expand the repertoire of strategies available for adapted WBRT in cases involving multiple brain metastases where stereotactic radiotherapy is not a viable option. Prospective ongoing studies assessing various memory-sparing radiotherapy techniques will define new standard of radiotherapy care of patients with multiple brain metastases.

Characterizing cognitive function in patients with autoimmune encephalitis: an Australian prospective study

OBJECTIVE

This study uses the Wechsler intelligence and memory scales to characterize the cognitive function of patients with autoimmune encephalitis (AE) in the chronic stage of the disease. AE is a group of neuroinflammatory disorders, and cognitive impairment is a significant source of chronic morbidity in these patients.

METHODS

Fifty patients with an average disease duration of 3.2 years after diagnosis were prospectively recruited from four hospitals. They underwent a comprehensive cognitive examination using the Wechsler Abbreviated Scale of Intelligence (WASI-II), Wechsler Adult Intelligence Scale (WAIS-IV) and Wechsler Memory Scale (WMS-IV). Summary statistics were computed, and single-sample and independent-samples t tests were used to compare the cohort to normative data.

RESULTS

The results revealed significantly reduced performances in perceptual reasoning, processing speed, and working memory among AE patients. Seropositive AE patients exhibited below-norm processing speed, while the seronegative group showed reduced working memory and processing speed. Delayed memory performance was significantly below expectations only in seronegative patients. Pattern analysis indicated that intact cognition was the most observed outcome after AE, but significant heterogeneity was observed among the impaired patients.

CONCLUSIONS

The study identified deficits in perceptual reasoning, processing speed, and working memory among chronic AE patients. Pattern analysis highlighted positive long-term cognitive outcomes for many but varied outcomes for those with ongoing difficulties. Although severely cognitively impaired patients were not included, the findings apply to  AE cohorts who attend outpatient clinical neuropsychology consultations emphasizing the need for thorough cognitive assessment. The results suggest a need for further research targeting other cognitive domains, including executive functions.

Outcomes after laser interstitial thermal ablation for temporal lobe epilepsy: a systematic review and meta-analysis

Epilepsy is a common condition that affects approximately 1% of the world's population, with about one-third being refractory epilepsy. Temporal lobe epilepsy is the most common type of drug-resistant epilepsy, and laser interstitial thermal therapy (LITT) is an innovative treatment. In this systematic review and meta-analysis, we aimed to summarize the current evidence on outcomes after LITT, including seizure freedom rate, complication rate, and neurocognitive outcome. PubMed and OVID Medline search engines were systematically searched for all indexed publications in the English language up to July15, 2023. The search was limited to human studies. Proportions and 95% confidence interval (CI) values were calculated for seizure, neurocognitive outcome, and complication rate. A total of 836 patients were included. Overall seizure outcomes, regardless of the pathology, included Engel I outcome in 56% (95% CI, 52.4-59.5%), Engel II outcome in 19.2% (95% CI, 15.4-23.6%), Engel III outcome in 17.3% (95% CI, 13.5-21.8%), and Engel IV outcome in 10.5% (95% CI 6.3-17%) of the patients. The overall decline in verbal and visual memory regardless of laterality was 24.2 (95% CI 8.6-52%) and 25.2% (8.3-55.8%). For naming, the decline was 13.4% (6.6-25.4%). The results of the pooled analysis in comparison with available data in the literature showed that seizure outcomes after LITT were slightly inferior to published data after temporal lobectomy. Data on cognitive outcomes after LITT are scarce and heterogeneous.

Cognitive function and the longitudinal hippocampal axis in mesial temporal sclerosis

OBJECTIVE

The relationship of preoperative memory deficits in patients with mesial temporal lobe epilepsy (mTLE) and hippocampal sclerosis (HS) to the distribution of neuronal loss is uncertain. Building on the material specificity theory, we tested the hypothesis that visual memory deficits are associated with posterior hippocampal atrophy, whereas verbal memory deficits are associated with anterior hippocampal atrophy.

METHODS

We studied 22 adults with mTLE and HS, calculating hippocampal head, body, and tail volumes, correcting for estimated total intracranial volume, using automated segmentation. Preoperative memory ability was evaluated with the Wechsler Memory Scale (WMS-II: logical memory, verbal paired associates, family pictures, and faces subtests). We correlated memory ability with hippocampal division volumes using SPSS 26.1 (repeated measures ANOVAs, one-way ANOVAs, Pearson r correlations) for statistical analysis.

RESULTS

We found a significant main effect of hippocampal subdivision, reporting volumetric differences between the head, body, and tail. Pairwise comparisons reported that the hippocampal head had significantly greater volume than both the body and tail (p < 0.001). For both left and right focus groups, the ipsilateral hippocampi were significantly smaller than the contralateral. Linear regression reported a left hippocampal model (head, body, and tail volumes) predicted performance on logical memory with the left hippocampal tail volume being the strongest predictor. A right hippocampal model (head, body, and tail volumes) predicted memory ability for family pictures and verbal paired associates at a trend level.

CONCLUSIONS

Ipsilateral hippocampal head and tail seem more vulnerable to injury than the body in both the left and right mTLE. Our study suggests there may be functional differences along the hippocampal longitudinal axis, particularly for the left hippocampal tail with verbal memory. Our findings are consistent with material-specific right-left differences in memory processing.

Neuropsychological function in psychosis of epilepsy

OBJECTIVE

The neuropsychological profile of patients with psychosis of epilepsy (POE) has received limited research attention. Recent neuroimaging work in POE has identified structural network pathology in the default mode network and the cognitive control network. This study examined the neuropsychological profile of POE focusing on cognitive domains subserved by these networks.

METHODS

Twelve consecutive patients with a diagnosis of POE were prospectively recruited from the Comprehensive Epilepsy Programmes at The Royal Melbourne, Austin and St Vincent's Hospitals, Melbourne, Australia between January 2015 and February 2017. They were compared to 12 matched patients with epilepsy but no psychosis and 42 healthy controls on standardised neuropsychological tests of memory and executive functioning in a case-control design.

RESULTS

Mean scores across all cognitive tasks showed a graded pattern of impairment, with the POE group showing the poorest performance, followed by the epilepsy without psychosis and the healthy control groups. This was associated with significant group-level differences on measures of working memory (p = < 0.01); immediate (p = < 0.01) and delayed verbal recall (p = < 0.01); visual memory (p < 0.001); and verbal fluency (p = 0.02). In particular, patients with POE performed significantly worse than the healthy control group on measures of both cognitive control (p = .005) and memory (p < .001), whereas the epilepsy without psychosis group showed only memory difficulties (delayed verbal recall) compared to healthy controls (p = .001).

CONCLUSION

People with POE show reduced performance in neuropsychological functions supported by the default mode and cognitive control networks, when compared to both healthy participants and people with epilepsy without psychosis.

Cortical microstructural gradients capture memory network reorganization in temporal lobe epilepsy

Temporal lobe epilepsy (TLE), one of the most common pharmaco-resistant epilepsies, is associated with pathology of paralimbic brain regions, particularly in the mesiotemporal lobe. Cognitive dysfunction in TLE is frequent, and particularly affects episodic memory. Crucially, these difficulties challenge the quality of life of patients, sometimes more than seizures, underscoring the need to assess neural processes of cognitive dysfunction in TLE to improve patient management. Our work harnessed a novel conceptual and analytical approach to assess spatial gradients of microstructural differentiation between cortical areas based on high-resolution MRI analysis. Gradients track region-to-region variations in intracortical lamination and myeloarchitecture, serving as a system-level measure of structural and functional reorganization. Comparing cortex-wide microstructural gradients between 21 patients and 35 healthy controls, we observed a reorganization of this gradient in TLE driven by reduced microstructural differentiation between paralimbic cortices and the remaining cortex with marked abnormalities in ipsilateral temporopolar and dorsolateral prefrontal regions. Findings were replicated in an independent cohort. Using an independent post-mortem dataset, we observed that in vivo findings reflected topographical variations in cortical cytoarchitecture. We indeed found that macroscale changes in microstructural differentiation in TLE reflected increased similarity of paralimbic and primary sensory/motor regions. Disease-related transcriptomics could furthermore show specificity of our findings to TLE over other common epilepsy syndromes. Finally, microstructural dedifferentiation was associated with cognitive network reorganization seen during an episodic memory functional MRI paradigm and correlated with interindividual differences in task accuracy. Collectively, our findings showing a pattern of reduced microarchitectural differentiation between paralimbic regions and the remaining cortex provide a structurally-grounded explanation for large-scale functional network reorganization and cognitive dysfunction characteristic of TLE.

Exploring the impact of hippocampal sclerosis on white matter tracts and memory in individuals with mesial temporal lobe epilepsy

OBJECTIVE

To investigate how the presence/side of hippocampal sclerosis (HS) are related to the white matter structure of cingulum bundle (CB), arcuate fasciculus (AF), and inferior longitudinal fasciculus (ILF) in mesial temporal lobe epilepsy (MTLE).

METHODS

We acquired diffusion-weighted magnetic resonance imaging (MRI) from 86 healthy and 71 individuals with MTLE (22 righ-HS; right-HS, 34 left-HS; left-HS, and 15 nonlesional MTLE). We utilized two-tensor tractography and fiber clustering to compare fractional anisotropy (FA) of each side/tract between groups. Additionally, we examined the association between FA and nonverbal (WMS-R) and verbal (WMS-R, RAVLT codification) memory performance for MTLE individuals.

RESULTS

White matter abnormalities depended on the side and presence of HS. The left-HS demonstrated widespread abnormalities for all tracts, the right-HS showed lower FA for ipsilateral tracts and the nonlesional MTLE group did not differ from healthy individuals. Results indicate no differences in verbal/nonverbal memory performance between the groups, but trend-level associations between higher FA of visual memory and the left CB (r = 0.286, P = 0.018), verbal memory (RAVLT) and -left CB (r = 0.335, P = 0.005), -right CB (r = 0.286, P = 0.016), and -left AF (r = 0.287, P = 0.017).

SIGNIFICANCE

Our results highlight that the presence and side of HS are crucial to understand the pathophysiology of MTLE. Specifically, left-sided HS seems to be related to widespread bilateral white matter abnormalities. Future longitudinal studies should focus on developing diagnostic and treatment strategies dependent on HS's presence/side.

Arousal deregulation in the co-shaping of neuropsychological dysfunction in frontal and mesial temporal lobe epilepsy

OBJECTIVE

Our work aims to investigate the role of physiological arousal in the expression of neuropsychological deficits in frontal lobe epilepsy (FLE) and mesial temporal lobe epilepsy (mTLE), by drawing on the Lurian theory of brain function.

METHODS

For this study a total of 43 patients with focal onset epilepsy has been taken; twenty-four patients with FLE, 19 patients with mTLE and 26 healthy controls, all matched for age and education. Participants underwent a comprehensive neuropsychological assessment including various cognitive domains, such as attention, episodic memory, speed of information processing, response inhibition and mental flexibility, working memory, verbal fluency (phonological & semantic).

RESULTS

There were no significant differences between FLE and mTLE patients in terms of neuropsychological performance. However, both FLE and mTLE patients showed significantly worse performance in several cognitive domains than HCs. The results seem to support our hypothesis that aberrant physiological arousal, as reflected in patients' worse performance in vigilance and attention, response inhibition, and processing speed, along with other disease-specific variables, may co-determine neuropsychological dysfunction and/or impairment in both FLE and mTLE.

CONCLUSION

Identifying a differential arousal-related neuropsychological affection in FLE and mTLE, among the known deleterious effects of the functional deficit zone and other disease-related variables, may further our understanding of the underlying cognitive-pathophysiological mechanisms in focal epilepsy syndromes.

What are we really predicting with fMRI in epilepsy surgery?

While memory and language functional magnetic resonance imaging (fMRI) paradigms are becoming evermore refined, the measures of outcome they predict following epilepsy surgery tend to remain single scores on pencil and paper tests that were developed decades ago and have been repeatedly shown to bear little relation to patients' subjective reports of memory problems in the real world. The growing imbalance between the increasing sophistication of the predictive paradigms on the one hand and the vintage measures of the outcome on the other in the fMRI epilepsy surgery literature threatens the clinical relevance of studies employing these technologies. This paper examines some of the core principles of assessing neuropsychological outcomes following epilepsy surgery and explores how these may be adapted and applied in fMRI study designs to maximize the clinical relevance of these studies.

Multifocal hypometabolic correlates to deficits of verbal memory in mesial temporal lobe epilepsy

BACKGROUND AND OBJECTIVES

Neuropsychological research on mesial temporal lobe epilepsy (MTLE) often highlights material-specific memory deficits, but a lesion-focused model may not accurately reflect the underlying networks that support episodic memory in these patients. Our study evaluated the pathophysiology behind verbal learning/memory deficits as revealed by hypometabolism quantified through 18-fluorodeoxyglucose positron emission tomography (FDG-PET).

METHODS

This retrospective study included thirty presurgical patients with intractable unilateral MTLE who underwent interictal FDG-PET and verbal memory assessment (12 females, mean age: 38.73 years). Fluorodeoxyglucose-positron emission tomography mapping was performed with voxel-based mapping of glucose utilization to a database of age-matched controls to derive regional Z-scores. Neuropsychological outcome variables included scores on learning and recall trials of two distinct verbal memory measures validated for use in epilepsy research. Pearson's correlations evaluated relationships between clinical variables and verbal memory. Linear regression was used to relate regional hypometabolism and verbal memory assessment. Post hoc analyses assessed areas of FDG-PET hypometabolism (threshold Z ≤ -1.645 below mean) where verbal memory was impaired.

RESULTS

Verbal memory deficits correlated with hypometabolism in limbic structures ipsilateral to language dominance but also correlated with hypometabolism in networks involving the ipsilateral perisylvian cortex and contralateral limbic and nonlimbic structures.

DISCUSSION

We conclude that traditional models of verbal memory may not adequately capture cognitive deficits in a broader sample of patients with MTLE. This study has important implications for epilepsy surgery protocols that use neuropsychological data and FDG-PET to draw conclusions about surgical risks.

Nonverbal memory tests revisited: Neuroanatomical correlates and differential influence of biasing cognitive functions

The detection of right temporal lobe dysfunction with nonverbal memory tests has remained difficult in the past. Reasons for this might be the potential influence of other biasing cognitive functions such as executive functions or the verbalisability of nonverbal material. The aim of this study was to investigate three classic nonverbal memory tests by identifying their neuroanatomical correlates with lesion-symptom mapping (LSM) and by probing their independence from verbal encoding abilities and executive functions. In a cohort of 119 patients with first-time cerebrovascular accident, memory performance was assessed in the Nonverbal Learning and Memory Test for Routes (NLMTR), the Rey Complex Figure Test (RCFT), and the Visual Design Learning Test (VDLT). Calculating multivariate LSM, we identified crucial brain structures for these three nonverbal memory tests. Behavioural analyses were performed to assess the impact of executive functions and verbal encoding abilities with regression analyses and likelihood-ratio tests. LSM revealed for the RCFT mainly right-hemispheric frontal, insular, subcortical, and white matter structures and for the NLMTR right-hemispheric temporal (hippocampus), insular, subcortical, and white matter structures. The VDLT did not reach significance in LSM analyses. Behavioural results showed that amongst the three nonverbal memory tests the impact of executive functions was most pronounced for RCFT, and the impact of verbal encoding abilities was most important in VDLT. Likelihood-ratio tests confirmed that only for NLMTR did the goodness of fit not significantly improve by adding executive functions or verbal encoding abilities. These results suggest that amongst the three nonverbal memory tests the NLMTR, as a spatial navigation test, could serve as the most suitable marker of right-hemispheric temporal lobe functioning, with the right hippocampus being involved only in this test. In addition, the behavioural results propose that only NLMTR seems mostly unaffected by executive functions and verbal encoding abilities.

The who, what, when and why of cognitive difficulties in epilepsy

Cognitive complaints are very common in people diagnosed with epilepsy. These difficulties are often another manifestation of the same pathology responsible for seizures. They can be further exacerbated by treatments aimed at seizure control. Other common comorbidities of epilepsy such as low mood and elevated anxiety can also contribute to cognitive complaints. There is surprisingly little overlap between memory complaints and performance on formal memory tests in this population. This article examines the multifactorial and heterogeneous nature of cognitive difficulties in epilepsy and makes the case for the provision of basic psychoeducation as the foundation for all interventions aimed at ameliorating these difficulties in this patient population.

Oscillations in the dentate gyrus as a tool for the performance of the hippocampal functions: Healthy and epileptic brain

The dentate gyrus (DG) is part of the hippocampal formation and is essential for important cognitive processes such as navigation and memory. The oscillatory activity of the DG network is believed to play a critical role in cognition. DG circuits generate theta, beta, and gamma rhythms, which participate in the specific information processing performed by DG neurons. In the temporal lobe epilepsy (TLE), cognitive abilities are impaired, which may be due to drastic alterations in the DG structure and network activity during epileptogenesis. The theta rhythm and theta coherence are especially vulnerable in dentate circuits; disturbances in DG theta oscillations and their coherence may be responsible for general cognitive impairments observed during epileptogenesis. Some researchers suggested that the vulnerability of DG mossy cells is a key factor in the genesis of TLE, but others did not support this hypothesis. The aim of the review is not only to present the current state of the art in this field of research but to help pave the way for future investigations by highlighting the gaps in our knowledge to completely appreciate the role of DG rhythms in brain functions. Disturbances in oscillatory activity of the DG during TLE development may be a diagnostic marker in the treatment of this disease.

White matter network organization predicts memory decline after epilepsy surgery

The authors have withdrawn their manuscript owing to a substantial change in data analysis and findings/conclusions. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

Theta tACS impairs episodic memory more than tDCS

Episodic memory deficits are a common consequence of aging and are associated with a number of neurodegenerative disorders (e.g., Alzheimer's disease). Given the importance of episodic memory, a great deal of research has investigated how we can improve memory performance. Transcranial electrical stimulation (TES) represents a promising tool for memory enhancement but the optimal stimulation parameters that reliably boost memory are yet to be determined. In our double-blind, randomised, sham-controlled study, 42 healthy adults (36 females; 23.3 ± 7.7 years of age) received anodal transcranial direct current stimulation (tDCS), theta transcranial alternating current stimulation (tACS) and sham stimulation during a list-learning task, over three separate sessions. Stimulation was applied over the left temporal lobe, as encoding and recall of information is typically associated with mesial temporal lobe structures (e.g., the hippocampus and entorhinal cortex). We measured word recall within each stimulation session, as well as the average number of intrusion and repetition errors. In terms of word recall, participants recalled fewer words during tDCS and tACS, compared to sham stimulation, and significantly fewer words recalled during tACS compared with tDCS. Significantly more memory errors were also made during tACS compared with sham stimulation. Overall, our findings suggest that TES has a deleterious effect on memory processes when applied to the left temporal lobe.

Is formal scoring better than just looking? A comparison of subjective and objective scoring methods of the Rey Complex Figure Test for lateralizing temporal lobe epilepsy

ObjectiveNeuropsychologists labor over scoring the Rey Complex Figure Test (RCFT), a measure of visuospatial functioning and nonverbal memory. Compelling arguments suggest that pathognomonic signs of the RCFT are observable to the "naked eye." Standard scoring systems are insensitive to lateralizing temporal lobe epilepsy (TLE) and alternative "qualitative" scoring systems are ineffective and time-consuming. Method: We examined accuracy of TLE lateralization using subjective classifications and standard scoring. Participants were 84 TLE patients (53 female; mean age₌36yrs) and 46 controls (27 female; mean age = 27.5). The former were classified as right (n = 41) or left (n = 43) TLE by neurologists using EEG and MRI studies. RCFT were scored using standard scoring with cut-offs of z ≤ -2 classified as impaired and were rated as "characteristic" of RTLE (Ugly) or LTLE (Not Ugly) performance by neuropsychologists. Accuracy of seizure lateralization for both methods was examined. Results: Neuropsychologists' ratings accuracy were at or below chance. Standard scoring criteria showed chance or slightly better lateralization prediction. Standard scoring predicted RTLE laterality more accurately than subjective ratings for copy trials; standard scoring was no better at lateralizing RTLE with delays. Subjective ratings were better at distinguishing TLE patients from controls. Conclusion: Findings highlight concerns regarding the usefulness of the RCFT in TLE lateralization, regardless of scoring approach.

Episodic memory network connectivity in temporal lobe epilepsy

OBJECTIVE

Temporal lobe epilepsy (TLE) affects brain networks and is associated with impairment of episodic memory. Temporal and extratemporal reorganization of memory functions is described in functional magnetic resonance imaging (fMRI) studies. Functional reorganizations have been shown at the local activation level, but network-level alterations have been underinvestigated. We aim to investigate the functional anatomy of memory networks using memory fMRI and determine how this relates to memory function in TLE.

METHODS

Ninety patients with unilateral TLE (43 left) and 29 controls performed a memory-encoding fMRI paradigm of faces and words with subsequent out-of-scanner recognition test. Subsequent memory event-related contrasts of words and faces remembered were generated. Psychophysiological interaction analysis investigated task-associated changes in functional connectivity seeding from the mesial temporal lobes (MTLs). Correlations between changes in functional connectivity and clinical memory scores, epilepsy duration, age at epilepsy onset, and seizure frequency were investigated, and between connectivity supportive of better memory and disease burden. Connectivity differences between controls and TLE, and between TLE with and without hippocampal sclerosis, were explored using these confounds as regressors of no interest.

RESULTS

Compared to controls, TLE patients showed widespread decreased connectivity between bilateral MTLs and frontal lobes, and increased local connectivity between the anterior MTLs bilaterally. Increased intrinsic connectivity within the bilateral MTLs correlated with better out-of-scanner memory performance in both left and right TLE. Longer epilepsy duration and higher seizure frequency were associated with decreased connectivity between bilateral MTLs and left/right orbitofrontal cortex (OFC) and insula, connections supportive of memory functions. TLE due to hippocampal sclerosis was associated with greater connectivity disruption within the MTL and extratemporally.

SIGNIFICANCE

Connectivity analyses showed that TLE is associated with temporal and extratemporal memory network reorganization. Increased bilateral functional connectivity within the MTL and connectivity to OFC and insula are efficient, and are disrupted by greater disease burden.

Testing an Adapted Auditory Verbal Learning Test Paradigm for fMRI to Lateralize Verbal Memory in Patients with Epilepsy

BACKGROUND AND PURPOSE

fMRI is a noninvasive tool for predicting postsurgical deficits in candidates with pharmacoresistant temporal lobe epilepsy. We aimed to test an adapted paradigm of the Rey Auditory Verbal Learning Test to evaluate differences in memory laterality indexes between patients and healthy controls and its association with neuropsychological scores.

MATERIALS AND METHODS

We performed a prospective study of 50 patients with temporal lobe epilepsy and 22 healthy controls. Participants underwent a block design language and memory fMRI. Laterality indexes and the hippocampal anterior-posterior index were calculated. Language and memory lateralization was organized into typical and atypical on the basis of laterality indexes. A neuropsychological assessment was performed with a median time from fMRI of 8 months and was compared with fMRI performance.

RESULTS

We studied 40 patients with left temporal lobe epilepsy and 10 with right temporal lobe epilepsy. Typical language occurred in 65.3% of patients and 90.9% of healthy controls (P = .04). The memory fMRI laterality index was obtained in all healthy controls and 92% of patients. The verbal memory laterality index was bilateral (24.3%) more frequently than the language laterality index (7.69%) in patients with left temporal lobe epilepsy. Atypical verbal memory was greater in patients with left temporal lobe epilepsy (56.8%) than in healthy controls (36.4%), and the proportion of bilateral laterality indexes (53.3%) was larger than right laterality indexes (46.7%). Atypical verbal memory might be associated with higher cognitive scores in patients. No relevant differences were seen in the hippocampal anterior-posterior index according to memory impairment.

CONCLUSIONS

The adapted Rey Auditory Verbal Learning Test paradigm fMRI might support verbal memory lateralization. Temporal lobe epilepsy laterality influences hippocampal memory laterality indexes. Left temporal lobe epilepsy has shown a higher proportion of atypical verbal memory compared with language, potentially to memory functional reorganization.

Does epilepsy always indicate worse outcomes? A longitudinal follow-up analysis of 485 glioma patients

BACKGROUND

Epilepsy is one of the most common glioma complications, and the two may be connected in more ways than we understand. We aimed to investigate the clinical features of glioma-associated epilepsy and explore the risk factors associated with it.

METHODS

We collected clinical information from 485 glioma patients in the Nanjing Brain Hospital and conducted 4 periodic follow-up visits. Based on the collected data, we analyzed the clinical characteristics of glioma patients with or without epilepsy and their relationship with survival.

RESULTS

Among glioma patients, younger people were more likely to have epilepsy. However, epilepsy incidence was independent of gender. Patients with grade II gliomas were most likely to develop epilepsy, while those with grade IV gliomas were least likely. There was no difference in Karnofsky Performance Status scores between patients with glioma-associated epilepsy and those without epilepsy. Additionally, epilepsy was independently associated with longer survival in the World Health Organization grade IV glioma patients. For grades II, III, and IV tumors, the 1-year survival rate of the epilepsy group was higher than that of the non-epilepsy group.

CONCLUSIONS

Epilepsy did not lead to worse admission performance and correlated with a better prognosis for patients with grade IV glioma.

Precision medicine in pediatric temporal epilepsy surgery: optimization of outcomes through functional MRI memory tasks and tailored surgeries

OBJECTIVE

The goal of epilepsy surgery is both seizure cessation and maximal preservation of function. In temporal lobe (TL) cases, the lack of functional MRI (fMRI) tasks that effectively activate mesial temporal structures hampers preoperative memory risk assessment, especially in children. This study evaluated pediatric TL surgery outcome optimization associated with tailored resection informed by an fMRI memory task.

METHODS

The authors identified focal onset TL epilepsy patients with 1) TL resections; 2) viable fMRI memory scans; and 3) pre- and postoperative neuropsychological (NP) evaluations. They retrospectively evaluated preoperative fMRI memory scans, available Wada tests, pre- and postoperative NP scores, postoperative MRI scans, and postoperative Engel class outcomes. To assess fMRI memory task outcome prediction, the authors 1) overlaid preoperative fMRI activation onto postoperative structural images; 2) classified patients as having "overlap" or "no overlap" of activation and resection cavities; and 3) compared these findings with memory improvement, stability, or decline, based on Reliable Change Index calculations.

RESULTS

Twenty patients met the inclusion criteria. At a median of 2.1 postoperative years, 16 patients had Engel class IA outcomes and 1 each had Engel class IB, ID, IIA, and IID outcomes. Functional MRI activation was linked to NP memory outcome in 19 of 20 cases (95%). Otherwise, heterogeneity characterized the cohort.

CONCLUSIONS

Functional MRI memory task activation effectively predicted individual NP outcomes in the context of tailored TL resections. Patients had excellent seizure and overall good NP outcomes. This small study adds to extant literature indicating that pediatric TL epilepsy does not represent a single clinical syndrome. Findings support individualized surgical intervention using fMRI memory activation to help guide this precision medicine approach.

The challenge of neuropsychological assessment of visual/visuo-spatial memory: A critical, historical review, and lessons for the present and future

A proliferation of tests exists for the assessment of auditory-verbal memory processes. However, from a clinical practice perspective, the situation is less clear when it comes to the ready availability of reliable and valid tests for the evaluation of visual/visuo-spatial memory processes. While, at face value, there appear to be a wide range of available tests of visual/visuo-spatial memory, utilizing different types of materials and assessment strategies, a number of criticisms have been, and arguably should be, leveled at the majority of these tests. The criticisms that have been directed toward what are typically considered to be visual/visuo-spatial memory tests, such as (1) the potential for verbal mediation, (2) over-abstraction of stimuli, (3) the requirement of a drawing response, and (4) the lack of sensitivity to unilateral brain lesions, mean that, in reality, the number of readily available valid tests of visual/visuo-spatial memory is, at best, limited. This article offers a critical, historical review on the existing measures and resources for the neuropsychological assessment of visual/visuo-spatial memory, and it showcases some examples of newer tests that have aimed to overcome the challenges of assessing these important aspects of memory. The article also identifies new trends and examples of how technological advances such as virtual reality may add value to overcome previous obstacles to assessment, thereby offering professionals more reliable, accurate means to evaluate visual/visuo-spatial memory in clinical practice.

Focal epilepsy disrupts spindle structure and function

Sleep spindles are the hallmark of N2 sleep and are attributed a key role in cognition. Little is known about the impact of epilepsy on sleep oscillations underlying sleep-related functions. This study assessed changes in the global spindle rate in patients with epilepsy, analysed the distribution of spindles in relation to the epileptic focus, and performed correlations with neurocognitive function. Twenty-one patients with drug-resistant focal epilepsy (12 females; mean age 32.6 ± 10.7 years [mean ± SD]) and 12 healthy controls (3 females; 24.5 ± 3.3 years) underwent combined whole-night high-density electroencephalography and polysomnography. Global spindle rates during N2 were lower in epilepsy patients compared to controls (mean = 5.78/min ± 0.72 vs. 6.49/min ± 0.71, p = 0.02, d =  − 0.70). Within epilepsy patients, spindle rates were lower in the region of the epileptic focus compared to the contralateral region (median = 4.77/min [range 2.53–6.18] vs. 5.26/min [2.53–6.56], p = 0.02, rank biserial correlation RC =  − 0.57). This decrease was driven by fast spindles (12–16 Hz) (1.50/min [0.62–4.08] vs. 1.65/min [0.51–4.28], p = 0.002, RC =  − 0.76). The focal reduction in spindles was negatively correlated with two scales of attention (r =  − 0.54, p = 0.01; r =  − 0.51, p = 0.025). Patients with focal epilepsy show a reduction in global and local spindle rates dependent on the region of the epileptic focus. This may play a role in impaired cognitive functioning. Future work will show if the local reduction in spindles can be used as potential marker of the epileptic focus.

Impaired Behavioral Pattern Separation in Refractory Temporal Lobe Epilepsy and Mild Cognitive Impairment

OBJECTIVE

Episodic memory impairment and hippocampal pathology are hallmark features of both temporal lobe epilepsy (TLE) and amnestic mild cognitive impairment (aMCI). Pattern separation (PS), which enables the distinction between similar but unique experiences, is thought to contribute to successful encoding and retrieval of episodic memories. Impaired PS has been proposed as a potential mechanism underling episodic memory impairment in aMCI, but this association is less established in TLE. In this study, we examined behavioral PS in patients with TLE and explored whether profiles of performance in TLE are similar to aMCI.

METHOD

Patients with TLE, aMCI, and age-matched, healthy controls (HCs) completed a modified recognition task that relies on PS for the discrimination of highly similar lure items, the Mnemonic Similarity Task (MST). Group differences were evaluated and relationships between clinical characteristics, California Verbal Learning Test-Second Edition scores, and MST performance were tested in the TLE group.

RESULTS

Patients with TLE and aMCI demonstrated poorer PS performance relative to the HCs, but performance did not differ between the two patient groups. Neither the side of seizure focus nor having hippocampal sclerosis affected performance in TLE. However, TLE patients with clinically defined memory impairment showed the poorest performance.

CONCLUSION

Memory performance on a task that relies on PS was disrupted to a similar extent in TLE and aMCI. The MST could provide a clinically useful tool for measuring hippocampus-dependent memory impairments in TLE and other neurological disorders associated with hippocampal damage.

One-year neuropsychological outcome after temporal lobe epilepsy surgery in large Czech sample: Search for factors contributing to memory decline

Background:

Assessment of cognitive functions is an integral part of the evaluation the efficacy of temporal resections. We studied postoperative neuropsychological changes and factors contributing to worse memory outcomes in patients who experienced a significant decline using reliable change indices.

Methods:

We prospectively studied 110 patients in whom we indicated anteromesial temporal resection (AMTR) and 46 patients who underwent selective amygdalohippocampectomy (SAHE). We administrated Wechsler Adult Intelligence Scale-Revised, Wechsler Memory Scale-Revised, and the Verbal Fluency Test before and 1 year after the operation.

Results:

At a group level, we did not observe any statistically significant changes in global, verbal, and visual MQ in either the AMTR or the SAHE group. At an individual level, we found a mean decrease of verbal MQ after left-sided AMTR by −4.43 points (P = 0.01). We detected no significant differences between the left and right side of surgery in the SAHE group. In patients with significant postoperative memory decline, we found either pre-existing extrahippocampal deficits/postoperative complications or incomplete hippocampal resection or a combination of these factors.

Conclusion:

In addition to the side of surgery, structural integrity and functional adequacy of resected hippocampus and volume of resected tissue and preoperative extrahippocampal lesions/postoperative complications also contribute to postoperative memory decline after temporal lobe epilepsy surgery.

The Amnestic Syndrome of Posterior Cerebral Artery Infarction

OBJECTIVE

Little is known about the character and underlying lesions of ischemic amnesia. We therefore studied episodic memory functions and brain lesions in 84 patients with acute ischemic infarcts in the supply territory of the posterior cerebral artery (PCA). We also aimed to learn how the neural memory systems are organized.

METHODS

Standard neuropsychological tests were used to assess verbal and figural memory. Patients were split in memory-impaired and memory-intact. Lesions were demarcated, normalized and anatomically labeled, using standard mapping procedures.

RESULTS

Of the 84 patients more than 80% had an amnestic syndrome, mostly with combined, less often with figural or verbal memory impairment. Amnesia in subjects with left hemispheric lesions was more frequent and more severe, with significantly lower scores on the verbal memory test. Normal performance or figural amnesia were prevalent after right hemispheric lesions. However, no amnesia subtype was strictly tied to left- or right-sided brain damage. Hippocampal and thalamic lesions were common, but 30% of lesions were extrahippocampal located in the ventral occipito-temporal cortex and long occipital white matter tracts. Most amnestic-patients lacked awareness for their memory impairment.

CONCLUSIONS

Memory impairment is a key clinical manifestation of acute PCA stroke. Amnesia is more frequent and more severe after left stroke, suggesting a left hemisphere dominance of the two memory systems. Domain specific memory appears not strictly lateralized, since deficits in verbal and figural memory were found after lesions of both sides. Extrahippocampal lesions may also cause memory impairment.

Temporal lobe interictal spikes disrupt encoding and retrieval of verbal memory: A subregion analysis

OBJECTIVE

The medial temporal lobe (MTL) encodes and recalls memories and can be a predominant site for interictal spikes (IS) in patients with focal epilepsy. It is unclear whether memory deficits are due to IS in the MTL producing a transient decline. Here, we investigated whether IS in the MTL subregions and lateral temporal cortex impact episodic memory encoding and recall.

METHODS

Seventy-eight participants undergoing presurgical evaluation for medically refractory focal epilepsy with depth electrodes placed in the temporal lobe participated in a verbal free recall task. IS were manually annotated during the pre-encoding, encoding, and recall epochs. We examined the effect of IS on word recall using mixed-effects logistic regression.

RESULTS

IS in the left hippocampus (odds ratio [OR] = .73, 95% confidence interval [CI] = .63-.84, p < .001) and left middle temporal gyrus (OR = .46, 95% CI = .27-.78, p < .05) during word encoding decreased subsequent recall performance. Within the left hippocampus, this effect was specific for area CA1 (OR = .76, 95% CI = .66-.88, p < .01) and dentate gyrus (OR = .74, 95% CI = .62-.89, p < .05). IS in other MTL subregions or inferior and superior temporal gyrus and IS occurring during the prestimulus window did not affect word encoding (p > .05). IS during retrieval in right hippocampal (OR = .22, 95% CI = .08-.63, p = .01) and parahippocampal regions (OR = .24, 95% CI = .07-.8, p < .05) reduced the probability of recalling a word.

SIGNIFICANCE

IS in medial and lateral temporal cortex contribute to transient memory decline during verbal episodic memory.

Disorganization of language and working memory systems in frontal versus temporal lobe epilepsy

Cognitive impairment is a common comorbidity of epilepsy and adversely impacts people with both frontal lobe (FLE) and temporal lobe (TLE) epilepsy. While its neural substrates have been investigated extensively in TLE, functional imaging studies in FLE are scarce. In this study, we profiled the neural processes underlying cognitive impairment in FLE and directly compared FLE and TLE to establish commonalities and differences. We investigated 172 adult participants (56 with FLE, 64 with TLE and 52 controls) using neuropsychological tests and four functional MRI tasks probing expressive language (verbal fluency, verb generation) and working memory (verbal and visuo-spatial). Patient groups were comparable in disease duration and anti-seizure medication load. We devised a multiscale approach to map brain activation and deactivation during cognition and track reorganization in FLE and TLE. Voxel-based analyses were complemented with profiling of task effects across established motifs of functional brain organization: (i) canonical resting-state functional systems; and (ii) the principal functional connectivity gradient, which encodes a continuous transition of regional connectivity profiles, anchoring lower-level sensory and transmodal brain areas at the opposite ends of a spectrum. We show that cognitive impairment in FLE is associated with reduced activation across attentional and executive systems, as well as reduced deactivation of the default mode system, indicative of a large-scale disorganization of task-related recruitment. The imaging signatures of dysfunction in FLE are broadly similar to those in TLE, but some patterns are syndrome-specific: altered default-mode deactivation is more prominent in FLE, while impaired recruitment of posterior language areas during a task with semantic demands is more marked in TLE. Functional abnormalities in FLE and TLE appear overall modulated by disease load. On balance, our study elucidates neural processes underlying language and working memory impairment in FLE, identifies shared and syndrome-specific alterations in the two most common focal epilepsies and sheds light on system behaviour that may be amenable to future remediation strategies.

Exploring the Semantic Structure of WMS-IV Verbal Paired Associates using the Hub-and-Spoke Model

OBJECTIVES

This study aimed to identify a well-fitting and theoretically justified item-level latent factor structure for the Wechsler Memory Scales (WMS)-IV verbal paired associates (VerbalPA) subtest to facilitate the ease and accuracy of score interpretations for patients with lateralized temporal lobe epilepsy (TLE).

METHODS

Archival data were used from 250 heterogeneous neurosciences patients who were administered the WMS-IV as part of a standard neuropsychological assessment. Three theoretically motivated models for the latent structure of VerbalPA were tested using confirmatory factor analysis. The first model, based on cognitive principles of semantic processing from hub-and-spoke theory, tested whether performance is related to specific semantic features of target words. The second, motivated by the Cattell-Horn-Carroll (CHC) model of cognitive abilities, investigated whether the associative properties of items influence performance. A third, Hybrid model tested whether performance is related to both semantic and associative properties of items. The best-fitting model was tested for diagnostic group effects contrasting the heterogeneous neuroscience patients with subsets of left and right TLE (n = 51, n = 26, respectively) patients.

RESULTS

The Hybrid model was found to have the best fit. Patients with left TLE scored significantly less well than the heterogeneous neurosciences sample on selected semantic factor scores, although the effect size was small.

CONCLUSIONS

Future editions of the WMS may consider implementing a semantic scoring structure for the VerbalPA to facilitate test score interpretation. Additionally, these results suggest that principles of hub-and-spoke theory may be integrated into CHC cognitive ability taxonomy.

Dynamic functional connectivity in modular organization of the hippocampal network marks memory phenotypes in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is a network disorder with a high incidence of memory impairment. Memory processing ability highly depends on the dynamic coordination between distinct modules within the hippocampal network. Here, we investigate the relationship between memory phenotypes and modular alterations of dynamic functional connectivity (FC) in the hippocampal network in TLE patients. Then, 31 healthy controls and 66 TLE patients with hippocampal sclerosis were recruited. The patients were classified into memory-intact (MI, 35 cases) group and memory-deficit (MD, 31 cases) group, each based on individual's Wechsler Memory Scale-Revised score. The sliding-windows approach and graph theory analysis were used to analyze the hippocampal network based on resting state functional magnetic resonance imaging. Temporal properties and modular metrics were calculated. Two discrete and switchable states were revealed: a high modularized state (State I) and a low modularized state (State II), which corresponded to either anterior or posterior hippocampal network dominated pattern. TLE was prone to drive less State I but more State II, and the tendency was more obvious in TLE-MD. Additionally, TLE-MD showed more widespread alterations of modular properties compared with TLE-MI across two states. Furthermore, the dynamic modularity features had unique superiority in discriminating TLE-MD from TLE-MI. These findings demonstrated that state transitions and modular function of dissociable hippocampal networks were altered in TLE and more importantly, they could reflect different memory phenotypes. The trend revealed potential values of dynamic FC in elucidating the mechanism underlying memory impairments in TLE.

The Spatial Learning Task of Lhermitte and Signoret (1972): Normative Data in Adults Aged 18-45

Objective

The Spatial Learning Task of Lhermitte and Signoret is an object-location arbitrary associative learning task. The task was originally developed to evaluate adults with severe amnesia. It is currently used in populations where the memory system either is not yet fully developed or where it has been compromised (e.g. epilepsy, traumatic brain injury, electroconvulsive therapy, cerebrovascular disease and dementia). Normative data have been published for paediatric cohorts and for older adults, however no data exist for the intervening adult years.

Method

Here, we address this gap, collecting normative data from 101 adults aged 18–45.

Results

Our data indicate that performance on the Spatial Learning Task is not influenced by age, gender, level of education or overall IQ. Less than 10% of the variance in learning scores is associated with variability in verbal memory. Ninety percent of participants achieved perfect scores on two successive trials (T2Cr) within five or fewer trials on the Spatial Learning Task. A T2Cr score of 6 is suggestive of impairment and a T2Cr score of 7 or more is statistically abnormal.

Conclusion

These data expand the clinical utility of the Spatial Learning Task in the adult population. Future work should examine performance in lower IQ cohorts, including intellectual disability, and explore sensitivity to disease factors such as laterality of mesial temporal lobe damage.

Accelerated long-term forgetting in children with temporal lobe epilepsy: A timescale investigation of material specificity and executive skills

Recently, children with temporal lobe epilepsy (TLE) were found to be at risk of accelerated long-term forgetting (ALF). In this study, we examined the temporal trajectory of ALF, while exploring the relationship between ALF, executive skills, and epilepsy variables. Fifty-one children, (23 with TLE and 28 typically developing) completed a battery of neuropsychological tests of verbal and visual memory, executive skills, and two experimental memory tasks (verbal and visual) involving recall after short (30-min) and extended (1-day and 2-week) delays. Side of seizure focus and hippocampal integrity were considered. On the visual task (Scene Memory), children with TLE performed comparably to typically developing children following a 30-min and 1-day delay, although worse than typically developing children at 2 weeks: ALF was observed in children with right TLE focus. The two groups did not differ on the experimental verbal memory task. Children with TLE also had worse performance than typically developing children on standardized verbal memory test and on tests of executive skills (i.e., verbal generativity, inhibition, working memory, complex attention). Only complex attention was associated with visual ALF. ALF was present for visuo-spatial materials in children with TLE at two weeks, and children with right TLE were most susceptible. A relationship was identified between complex attention and long-term forgetting. The findings extend our understanding of difficulties in long-term memory formation experienced by children with TLE.

Association Between Microstructural Asymmetry of Temporal Lobe White Matter and Memory Decline After Anterior Temporal Lobectomy

BACKGROUND AND OBJECTIVES

Risk for memory decline is a substantial concern in patients with temporal lobe epilepsy (TLE) undergoing anterior temporal lobectomy (ATL). Although prior studies have identified associations between memory and integrity of white matter (WM) networks within the medial temporal lobe (MTL) preoperatively, we contribute a study examining whether microstructural asymmetry of deep and superficial WM networks within the MTL predicts postoperative memory decline.

METHODS

Patients with drug-resistant TLE were recruited from 2 epilepsy centers in a prospective longitudinal study. All patients completed preoperative T1 and diffusion-weighted MRI (DWI) as well as preoperative and postoperative neuropsychological testing. Preoperative fractional anisotropy (FA) of the WM directly beneath the neocortex (i.e., superficial WM [SWM]) and of deep WM tracts associated with memory were calculated. Asymmetry was calculated for hippocampal volume and FA of each WM tract or region and examined in linear and logistic regressions with preoperative to postoperative memory change as the primary outcome.

RESULTS

Data were analyzed from 42 patients with TLE (19 left TLE [LTLE], 23 right TLE [RTLE]) who underwent ATL. Leftward FA asymmetry of the entorhinal SWM was associated with decline on prose and associative recall in LTLE, whereas leftward FA asymmetry of the uncinate fasciculus (UNC) was associated with decline on prose recall only. After controlling for preoperative memory score and hippocampal volume, leftward FA asymmetry of the entorhinal SWM uniquely contributed to decline in both prose and associative recall (β = -0.46; SE 0.14 and β = -0.68; SE 0.22, respectively) and leftward FA asymmetry of the UNC uniquely contributed to decline in prose recall (β = -0.31; SE 0.14). A model combining asymmetry of hippocampal volume and entorhinal FA correctly classified memory outcomes in 79% of patients with LTLE for prose (area under the curve [AUC] 0.89; sensitivity 82%; specificity 75%) and 81% of patients for associative (AUC 0.79; sensitivity 83%; specificity 80%) recall. Entorhinal SWM asymmetry was the strongest predictor in both models.

DISCUSSION

Preoperative asymmetry of deep WM and SWM integrity within the MTL is a strong predictor of postoperative memory decline in TLE, suggesting that surgical decision-making may benefit from considering each patient's WM network adequacy and reserve in addition to hippocampal integrity.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that preoperative asymmetry of deep WM and SWM integrity within the MTL is a predictor of postoperative memory decline.

Spatial Binding Impairments in Visual Working Memory following Temporal Lobectomy

Disorders of the medial temporal lobe (MTL) adversely affect visual working memory (vWM) performance, including feature binding. It is unclear whether these impairments generalize across visual dimensions or are specifically spatial. To address this issue, we compared performance in two tasks of 13 epilepsy patients, who had undergone a temporal lobectomy, and 15 healthy controls. In the vWM task, participants recalled the color of one of two polygons, previously displayed side by side. At recall, a location or shape probe identified the target. In the perceptual task, participants estimated the centroid of three visible disks. Patients recalled the target color less accurately than healthy controls because they frequently swapped the nontarget with the target color. Moreover, healthy controls and right temporal lobectomy patients made more swap errors following shape than space probes. Left temporal lobectomy patients, showed the opposite pattern of errors instead. Patients and controls performed similarly in the perceptual task. We conclude that left MTL damage impairs spatial binding in vWM, and that this impairment does not reflect a perceptual or attentional deficit.

Multimodal connectome biomarkers of cognitive and affective dysfunction in the common epilepsies

Epilepsy is one of the most common chronic neurological conditions, traditionally defined as a disorder of recurrent seizures. Cognitive and affective dysfunction are increasingly recognized as core disease dimensions and can affect patient well-being, sometimes more than the seizures themselves. Connectome-based approaches hold immense promise for revealing mechanisms that contribute to dysfunction and to identify biomarkers. Our review discusses emerging multimodal neuroimaging and connectomics studies that highlight network substrates of cognitive/affective dysfunction in the common epilepsies. We first discuss work in drug-resistant epilepsy syndromes, that is, temporal lobe epilepsy, related to mesiotemporal sclerosis (TLE), and extratemporal epilepsy (ETE), related to malformations of cortical development. While these are traditionally conceptualized as ‘focal’ epilepsies, many patients present with broad structural and functional anomalies. Moreover, the extent of distributed changes contributes to difficulties in multiple cognitive domains as well as affective-behavioral challenges. We also review work in idiopathic generalized epilepsy (IGE), a subset of generalized epilepsy syndromes that involve subcortico-cortical circuits. Overall, neuroimaging and network neuroscience studies point to both shared and syndrome-specific connectome signatures of dysfunction across TLE, ETE, and IGE. Lastly, we point to current gaps in the literature and formulate recommendations for future research.

Epilepsy is increasingly recognized as a network disorder characterized by recurrent seizures as well as broad-ranging cognitive difficulties and affective dysfunction. Our manuscript reviews recent literature highlighting brain network substrates of cognitive and affective dysfunction in common epilepsy syndromes, namely temporal lobe epilepsy secondary to mesiotemporal sclerosis, extratemporal epilepsy secondary to malformations of cortical development, and idiopathic generalized epilepsy syndromes arising from subcortico-cortical pathophysiology. We discuss prior work that has indicated both shared and distinct brain network signatures of cognitive and affective dysfunction across the epilepsy spectrum, improves our knowledge of structure-function links and interindividual heterogeneity, and ultimately aids screening and monitoring of therapeutic strategies.

A clinically applicable functional MRI memory paradigm for use with pediatric patients

OBJECTIVE

Clinically employable functional MRI (fMRI) memory paradigms are not yet established for pediatric patient epilepsy surgery workups. Seeking to establish such a paradigm, we evaluated the effectiveness of memory fMRI tasks we developed by quantifying individual activation in a clinical pediatric setting, analyzing patterns of activation relative to the side of temporal lobe (TL) pathology, and comparing fMRI and Wada test results.

METHODS

We retrospectively identified 72 patients aged 6.7-20.9 years with pathology (seizure focus and/or tumor) limited to the TL who had attempted memory and language fMRI tasks over a 9-year period as part of presurgical workups. Memory fMRI tasks required visualization of autobiographical memories in a block design alternating with covert counting. Language fMRI protocols involved verb and sentence generation. Scans were both qualitatively interpreted and quantitatively assessed for blood oxygenation level dependent (BOLD) signal change using region of interest (ROI) masks. We calculated the percentage of successfully scanned individual cases, compared 2 memory task activation masks in cases with left versus right TL pathology, and compared fMRI with Wada tests when available. Patients who had viable fMRI and Wada tests had generally concordant results.

RESULTS

Of the 72 cases, 60 (83%), aged 7.6-20.9 years, successfully performed the memory fMRI tasks and 12 (17%) failed. Eleven of 12 unsuccessful scans were due to motion and/or inability to perform the tasks, and the success of a twelfth was indeterminate due to orthodontic metal artifact. Seven of the successful 60 cases had distorted anatomy that precluded employing predetermined masks for quantitative analysis. Successful fMRI memory studies showed bilateral mesial temporal activation and quantitatively demonstrated: (1) left activation (L-ACT) less than right activation (R-ACT) in cases with left temporal lobe (L-TL) pathology, (2) nonsignificant R-ACT less than L-ACT in cases with right temporal lobe (R-TL) pathology, and (3) lower L-ACT plus R-ACT activation for cases with L-TL versus R-TL pathology. Patients who had viable fMRI and Wada tests had generally concordant results.

SIGNIFICANCE

This study demonstrates evidence of an fMRI memory task paradigm that elicits reliable activation at the individual level and can generally be accomplished in clinically involved pediatric patients. This autobiographical memory paradigm showed activation in mesial TL structures, and cases with left compared to right TL pathology showed differences in activation consistent with extant literature in TL epilepsy. Further studies will be required to assess outcome prediction.

Uses and abuses of the neuropsychological assessment in the presurgical evaluation of epilepsy surgery candidates

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Results from the neuropsychological assessment must be integrated into the wider clinical picture for all epilepsy surgery candidates.

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Motivation for surgery must be fully explored to ensure informed consent, even in ‘ideal’ surgical candidates.

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Inappropriate weight should not be given to standalone neuropsychological scores in the surgical decision making process.

Recent guidelines from the International League Against Epilepsy (ILAE) delineating the role of the neuropsychologist in the assessment of epilepsy surgery patients stress the collaborative contribution neuropsychologists should make to seizure characterization, lateralization and localization in the pre-surgical setting. The role they should play in the comprehensive counselling of surgical candidates, including exploration of the patient’s expectations of surgical treatment is also mandated. In this paper we present two contrasting case studies which illustrate the importance of these roles and the impact they can have on patient outcomes. In Case A we describe the patient journey of a 69-year-old women with left hippocampal sclerosis and concordant neurophysiology and seizure semiology. We present the series of discussions and decisions which led her to reject the surgical option following a detailed exploration of her motivations for surgery and the likely cognitive consequences of the procedure. In Case B we describe the series of errors and omissions which led to the failure of a clinical team to correctly interpret and integrate neuropsychological findings into the larger clinical picture of a 19-year-old woman with a seven year history of seizures. These errors ultimately culminated in the patient undergoing a right temporal lobe resection to treat psychogenic nonepileptic seizures (PNES).

The extent of integration of the data from the clinical neuropsychological assessment in the full presurgical evaluation was critical in determining the outcomes in both of these cases. Surgery did not solve Case B’s problems and left her with the lifelong cognitive vulnerabilities that are associated with unilateral temporal lobe resection. In contrast, Case A was a good surgical candidate, but comprehensive integration of the neuropsychological findings into the larger clinical picture established that surgery was not the best solution to the problem she wished to solve.

Neuropsychology of temporal lobe epilepsies

This chapter focuses on the neuropsychology of adults with temporal lobe epilepsy (TLE). First, a thorough description of the brain-behavior relationship characterizing focal TLE with and without hippocampal sclerosis is presented. Then, the aim and the specificity of the NPA in the care of epilepsy are described. Considering the high frequency of medically intractable TLE that can be treated by surgery, an assessment carried out in the context of pre- and postoperative evaluation is presented and discussed in light of insights from functional neuroimaging findings. Finally, we propose concluding remarks about the place of neuropsychology in the care of epilepsy in improving our understanding of the cognitive and emotional phenotypes associated with TLE.