Relationship of age at onset, chronologic age, and adequacy of preoperative performance to verbal memory change after anterior temporal lobectomy

Stability of face recognition abilities after left or right anterior temporal lobectomy

Patients with anterior temporal lobe (ATL) resection due to mesial temporal lobe epilepsy (MTLE) have difficulties at identifying familiar faces and explicitly remembering newly learned faces but their ability to individuate unfamiliar faces remains largely unknown. Moreover, the extent to which their difficulties with familiar face identity recognition and learning is truly due to the ATL resection remains unknown. Here, we report a study of 24 MTLE patients and matched healthy controls tested with an extensive set of seven face and visual object recognition tasks (including three tasks evaluating unfamiliar face individuation) before and about 6 months after unilateral (nine left, 15 right) ATL resection. We found that ATL resection has little or no effect on the patients' preserved pre-surgical ability to perform unfamiliar face individuation, both at the group and individual levels. More surprisingly, ATL resection also has little effect on the patients' performance at recognizing and naming famous faces as well as at learning new faces. A substantial proportion of right MTLE patients (33%) even improved their response times on several tasks, which may indicate a functional release of visuo-spatial processing after resection in the right ATL. Altogether this study shows that face recognition abilities are mainly unaffected by ATL resection in MTLE, either because the critical regions for face recognition are spared or because performance at some tasks is already lower than normal preoperatively. Overall, these findings urge caution when interpreting the causal effect of brain lesions on face recognition ability in patients with ATL resection due to MTLE. They also illustrate the complexity of predicting cognitive outcomes after epilepsy surgery because of the influence of many different intertwined factors.

Bilateral ictal EEG is associated with better memory outcome after hippocampal sclerosis surgery

OBJECTIVE

To compare memory outcomes after surgery for unilateral hippocampal sclerosis (HS)-associated epilepsy in patients with unilateral and bilateral ictal electrographic involvement.

METHODS

We prospectively evaluated HS patients, aged 18-55 years and IQ ≥70. Left (L) and right (R) surgical groups underwent noninvasive video-EEG monitoring and Wada test. We classified patients as Ipsilateral if ictal EEG was restricted to the HS side, or Bilateral, if at least one seizure onset occurred contralaterally to the HS, or if ictal discharge evolved to the opposite temporal region. Patients who declined surgery served as controls. Memory was evaluated on two occasions with Rey Auditory-Verbal Learning Test and Rey Visual-Design Learning Test. Baseline neuropsychological test scores were compared between groups. Pre- and postoperative scores were compared within each group. Reliable change index Z-scores (RCI) were obtained using controls as references, and compared between surgical groups.

RESULTS

We evaluated 64 patients. Patients were classified as: L-Ipsilateral (9), L-Bilateral (15), L-Control (9), R-Ipsilateral (10), R-Bilateral (9), and R-Control (12). On preoperative evaluation, memory performance did not differ among surgical groups. Right HS patients did not present postoperative memory decline. L-Ipsilateral group presented postoperative decline on immediate (P = 0.036) and delayed verbal recall (P = 0.011), while L-Bilateral did not decline. L-Ipsilateral had lower RCI Z-scores, indicating delayed verbal memory decline compared to L-Bilateral (P = 0.012).

SIGNIFICANCE

Dominant HS patients with bilateral ictal involvement presented less pronounced postoperative verbal memory decline compared to patients with exclusive ipsilateral ictal activity. Surgery was indicated in these patients regardless of memory impairment on neuropsychological testing, since resection of the left sclerotic hippocampus could result in cessation of contralateral epileptiform activity, and, therefore, improved memory function.

Language MEG predicts postoperative verbal memory change in left mesial temporal lobe epilepsy

OBJECTIVE

To clarify whether preoperative language magnetoencephalography (MEG) predicts postoperative verbal memory (VM) changes in left mesial temporal lobe epilepsy (LMTLE).

METHODS

We reviewed 18 right-handed patients with LMTLE who underwent anterior temporal lobectomy or selective amygdala hippocampectomy, 12 with (HS+) and 6 without hippocampal sclerosis (HS-). Patients underwent neuropsychological assessment before and after surgery. MEG was measured with an auditory verbal learning task in patients preoperatively and in 15 right-handed controls. Dynamic statistical parametric mapping (dSPM) was used for source imaging of task-related activity. Language laterality index (LI) was calculated by z-score of dSPM in language-related regions. LI in the region of HS+ and HS- was compared to controls. The correlation between LI and postoperative VM change was assessed in HS+ and HS-.

RESULTS

Preoperative LI in supramarginal gyrus showed greater right-shifted lateralization in both HS+ and HS- than in controls. Right-shifted LI in supramarginal gyrus was correlated with postoperative VM increase in HS+ (p = 0.019), but not in HS-.

CONCLUSIONS

Right-shifted language lateralization in dSPM of MEG signals may predict favorable VM outcome in HS+ of LMTLE.

SIGNIFICANCE

Findings warrant further investigation of the relation between regional language laterality index and postoperative verbal memory changes.

A Comparison of Neuropsychological Outcomes following Responsive Neurostimulation and Anterior Temporal Lobectomy in Drug-Resistant Epilepsy

Neuropsychological outcomes following temporal lobe resection for drug-resistant epilepsy (DRE) are well established. For instance, left anterior temporal lobectomy (LATL) is associated with a greater risk for cognitive morbidity compared to right (RATL). However, the impact of neuromodulatory devices, specifically responsive neurostimulation (RNS), remains an area of active interest. There are currently no head-to-head comparisons of neuropsychological outcomes after surgical resection and neuromodulation. This study reports on a cohort of 21 DRE patients with the RNS System who received comprehensive pre- and post-implantation neuropsychological testing. We compared both cognitive and seizure outcomes in the RNS group to those of 307 DRE patients who underwent LATL (n = 138) or RATL (n = 169). RNS patients had higher seizure rates pre-intervention. While fewer in the RNS group achieved Class I Engel outcomes compared to the ATL cohorts, RNS patients also showed seizure frequency declines from pre- to post-intervention that were similar to those who underwent resective surgery. Moreover, the RNS and RATL groups were similar in their neuropsychological outcomes, showing no significant cognitive decline post-intervention. In contrast, the LATL group notably declined in object naming and verbal list learning. Direct comparisons like this study may be used to guide clinicians in shared decision making to tailor management plans for patients' overall treatment goals.

Clinical recommendations for conducting pediatric functional language and memory mapping during the phase I epilepsy presurgical workup

Objective: Pediatric epilepsy surgery effectively controls seizures but may risk cognitive, language, or memory decline. Historically, the intra-carotid anesthetic procedure (IAP or Wada Test) was pivotal for language and memory function. However, advancements in noninvasive mapping, notably functional magnetic resonance imaging (fMRI), have transformed clinical practice, reducing IAP's role in presurgical evaluations. Method: We conducted a critical narrative review on mapping technologies, including factors to consider for discordance. Results: Neuropsychological findings suggest that if pre-surgery function remains intact and the surgery targets the eloquent cortex, there is a high chance for decline. Memory and language decline are particularly pronounced post-left anterior temporal lobe resection (ATL), making presurgical cognitive assessment crucial for predicting postoperative outcomes. However, the risk of functional decline is not always clear - particularly with higher rates of atypical organization in pediatric epilepsy patients and discordant findings from cognitive mapping. We found little research to date on the use of IAP and other newer technologies for lateralization/localization in pediatric epilepsy. Based on this review, we introduce an IAP decision tree to systematically navigate discordance in IAP decisions for epilepsy presurgical workup. Conclusions: Future research should be aimed at pediatric populations to improve the precision of functional mapping, determine which methods predict post-surgical deficits and then create evidence-based practice guidelines to standardize mapping procedures. Explicit directives are needed for resolving conflicts between developing mapping procedures and established clinical measures. The proposed decision tree is the first step to standardize when to consider IAP or invasive mapping, in coordination with the multidisciplinary epilepsy surgical team.

Anterolateral temporal lobe localization of dysnomia after temporal lobe epilepsy surgery

Objectives

To evaluate what factors influence naming ability after temporal lobectomy in patients with drug-resistant epilepsy.

Methods

85 participants with drug-resistant epilepsy who underwent temporal lobe (TL) resective surgery were retrospectively identified (49 left TL and 36 right TL). Naming ability was assessed before and >3 months post-surgery using the Boston Naming Test (BNT).Multivariate lesion-symptom mapping was performed to evaluate whether lesion location related to naming deficits. Multiple regression analyses were conducted to examine if other patient characteristics were significantly associated with pre-to post-surgery changes in naming ability.

Results

Lesion laterality and location were important predictors of post-surgical naming performance. Naming performance significantly improved after right temporal lobectomy ( p = 0.015) while a decrement in performance was observed following left temporal lobectomy ( p = 0.002). Lesion-symptom mapping showed the decline in naming performance was associated with surgical resection of the anterior left middle temporal gyrus (Brodmann area 21, r =0.41, p = <.001). For left hemisphere surgery, later onset of epilepsy was associated with a greater reduction in post-surgical naming performance ( p = 0.01).

Significance

There is a wide range of variability in outcomes for naming ability after temporal lobectomy, from significant improvements to decrements observed. If future studies support the association of left anterior middle temporal gyrus resection and impaired naming this may help in surgical planning and discussions of prognosis.

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.

Hyperphosphorylated Tau in Mesial Temporal Lobe Epilepsy: a Neuropathological and Cognitive Study

Temporal lobe epilepsy (TLE) often courses with cognitive deficits, but its underlying neuronal basis remains unclear. Confluent data suggest that epilepsy share pathophysiological mechanisms with neurodegenerative diseases. However, as most studies analyze subjects 60 years old and older, it is challenging to rule out that neurodegenerative changes arise from age-related mechanisms rather than epilepsy in these individuals. To fill this gap, we conducted a neuropathological investigation of the hippocampal formation of 22 adults with mesial TLE and 20 age- and sex-matched controls (both younger than 60 years). Moreover, we interrogated the relationship between these neuropathological metrics and cognitive performance. Hippocampal formation extracted from patients with drug-resistant mesial TLE undergoing surgery and postmortem non-sclerotic hippocampal formation of clinically and neuropathologically controls underwent immunohistochemistry against amyloid β (Aβ), hyperphosphorylated tau (p-tau), and TAR DNA-binding protein-43 (TDP-43) proteins, followed by quantitative analysis. Patients underwent a comprehensive neuropsychological evaluation prior to surgery. TLE hippocampi showed a significantly higher burden of p-tau than controls, whereas Aβ deposits and abnormal inclusions of TDP-43 were absent in both groups. Patients with hippocampal sclerosis (HS) type 2 had higher immunostaining for p-tau than patients with HS type 1. In addition, p-tau burden was associated with impairment in attention tasks and seizures frequency. In this series of adults younger than 60 years-old, the increase of p-tau burden associated with higher frequency of seizures and attention impairment suggests the involvement of tau pathology as a potential contributor to cognitive deficits in mesial TLE.

Correlation of age at seizure onset with GABAA receptor subunit and chloride Co-transporter configuration in Focal cortical dysplasia (FCD)

Focal cortical dysplasia (FCD) represents a group of malformations of cortical development, which are speculated to be related to early developmental defects in the cerebral cortex. According to dysmature cerebral development hypothesis of FCD altered GABAA receptor function is known to contribute to abnormal neuronal network. Here, we studied the possible association between age at seizure onset in FCD with the subunit configuration of GABAA receptors in resected brain specimens obtained from patients with FCD. We observed a significantly higher ratio of α4/α1 subunit-containing GABAA receptors in patients with early onset (EO) FCD as compared to those with late onset (LO) FCD as is seen during the course of development where α4-containing GABAA receptors expression is high as compared to α1-containing GABAA receptors expression. Likewise, the influx to efflux chloride co-transporter expression of NKCC1/KCC2 was also increased in patients with EO FCD as seen during brain development. In addition, we observed that the ratio of GABA/Glutamate neurotransmitters was lower in patients with EO FCD as compared to that in patients with LO FCD. Our findings suggest altered configuration of GABAA receptors in FCD which could be contributing to aberrant depolarizing GABAergic activity. In particular, we observed a correlation of age at seizure onset in FCD with subunit configuration of GABAA receptors, levels of NKCC1/KCC2 and the ratio of GABA/Glutamate neurotransmitters such that the patients with EO FCD exhibited a more critically modulated GABAergic network.

WADA test for postoperative memory prediction in left TLE. Is it still useful in the 21st century?

BACKGROUND

Epilepsy surgery offers an effective treatment to achieve seizure freedom in refractory temporal lobe epilepsy. Since left temporal lobe surgery can be associated with verbal memory deterioration, control of cognitive decline is a main goal of therapy. This study analyzes the prognostic value of intracarotid amobarbital procedure (Wada test) in addition to specific neuropsychological and clinical variables for postoperative memory changes.

METHOD

Between 2013 and 2021 thirty-six patients (18 females, 18 males, mean age 41.0 years) from the Epilepsy Center Erlangen (ECE) with left hemispheric temporal lobe epilepsy underwent neuropsychological assessment preoperatively - including the Wada test - and six months postoperatively. In addition, a group of 92 patients (40 females, 52 males, mean age 36.1 years) with left or right hemispheric focus who underwent Wada test and surgery before 2013 was included as a standardization group. In all patients Wada test was carried out preoperatively to determine language dominance and memory capacity.

RESULTS

Postoperative verbal memory scores showed no significant difference from preoperative performance. Preoperative verbal memory performance as well as the hippocampal resection extent is particularly important in predicting postoperative verbal memory change. After left temporal lobe surgery, a significantly higher postoperative functional level was shown for figural memory. Specifically, a good contralateral hemispheric performance level assessed by the Wada test proved to be a compensatory factor for postoperative losses.

CONCLUSION

The Wada test is no longer necessary as a diagnostic tool for a broad group of patients with temporal lobe epilepsy. However, it can be useful for a subgroup of patients with clinical indicators such as nonspecific or incongruent preoperative verbal and figural memory impairments. In this study, Wada test data about the functional level of the contralateral hemisphere specifically allowed estimation of postoperative figural memory changes.

Task-based functional magnetic resonance imaging prediction of postsurgical cognitive outcomes in temporal lobe epilepsy: A systematic review, meta-analysis, and new data

Task-based functional magnetic resonance imaging (tfMRI) has developed as a common alternative in epilepsy surgery to the intracarotid amobarbital procedure, also known as the Wada procedure. Prior studies have implicated tfMRI as a comparable predictor of postsurgical cognitive outcomes. However, the predictive validity of tfMRI has not been established. This preregistered systematic review and meta-analysis (CRD42020183563) synthesizes the literature predicting postsurgical cognitive outcomes in temporal lobe epilepsy (TLE) using tfMRI. The PubMed and PsycINFO literature databases were queried for English-language articles published between January 1, 2009 and December 31, 2020 associating tfMRI laterality indices or symmetry of task activation with outcomes in TLE. Their references were reviewed for additional relevant literature, and unpublished data from our center were incorporated. Nineteen studies were included in the meta-analysis. tfMRI studies predicted postsurgical cognitive outcomes in left TLE ( ρ ̂ = -.27, 95% confidence interval [CI] = -.32 to -.23) but not right TLE ( ρ ̂ = -.02, 95% CI = -.08 to .03). Among studies of left TLE, language tfMRI studies were more robustly predictive of postsurgical cognitive outcomes ( ρ ̂ = -.27, 95% CI = -.33 to -.20) than memory tfMRI studies ( ρ ̂ = -.27, 95% CI = -.43 to -.11). Further moderation by cognitive outcome domain indicated language tfMRI predicted confrontation naming ( ρ ̂ = -.32, 95% CI = -.41 to -.22) and verbal memory ( ρ ̂ = -.26, 95% CI = -.35 to -.17) outcomes, whereas memory tfMRI forecasted only verbal memory outcomes ( ρ ̂ = -.37, 95% CI = -.57 to -.18). Surgery type, birth sex, level of education, age at onset, disease duration, and hemispheric language dominance moderated study outcomes. Sensitivity analyses suggested the interval of postsurgical follow-up, and reporting and methodological practices influenced study outcomes as well. These findings intimate tfMRI is a modest predictor of outcomes in left TLE that should be considered in the context of a larger surgical workup.

Reliable change on the selective reminding test in a series of left-hemisphere language dominant patients with right temporal lobe epilepsy

The Selective Reminding Test (SRT) is widely used in pre-surgical evaluations for people with epilepsy; however, important characteristics such as reliability and stability over time within an epilepsy-specific control cohort are unclear. In this study, we document test-retest reliabilities, practice effects, and Reliable Change Indices (RCI) for this test in a sample of right temporal lobe epilepsy patients who are left hemisphere dominant for language and underwent surgical resection on the right temporal lobe. A sample of 101 adults with a right temporal lobe seizure focus (mean age = 38.5) was administered the SRT pre- and post-right temporal lobe surgery. Test-retest reliabilities were modest (r = 0.44-0.59). Practice effects were minimal (0.25-2.04). Reliable Change Indices were calculated and ranged from 4 to 26 depending on the SRT index. The RCI's indicate that relatively moderate to large changes on the SRT are needed for a change score to be considered a significant change in an individual's performance. The RCIs can be used to detect a reliable change in patients undergoing left temporal lobe epilepsy surgery who are at significant risk for verbal memory decline.

The Impact of Right Temporal Lobe Epilepsy On Nonverbal Memory: Meta-regression of Stimulus- and Task-related Moderators

Nonverbal memory tests have great potential value for detecting the impact of lateralized pathology and predicting the risk of memory loss following right temporal lobe resection (TLR) for temporal lobe epilepsy (TLE) patients, but this potential has not been realized. Previous reviews suggest that stimulus type moderates the capacity of nonverbal memory tests to detect right-lateralized pathology (i.e., faces > designs), but the roles of other task-related factors have not been systematically explored. We address these limitations using mixed model meta-regression (k = 158) of right-lateralization effects (right worse than left TLE) testing the moderating effects of: 1) stimulus type (designs, faces, spatial), 2) learning format (single trial, repeated trials), 3) testing delay (immediate or long delay), and 4) testing format (recall, recognition) for three patient scenarios: 1) presurgical, 2) postsurgical, and 3) postsurgical change. Stimulus type significantly moderated the size of the right-lateralization effect (faces > designs) for postsurgical patients, test format moderated the size of the right-lateralization effect for presurgical-postsurgical change (recognition > recall) but learning format and test delay had no right-lateralization effect for either sample. For presurgical patients, none of the task-related factors significantly increased right-lateralization effects. This comprehensive review reveals the value of recognition testing in gauging the risk of nonverbal memory decline.

Practical Aspects of Functional Magnetic Resonance Imaging in Children

Functional magnetic resonance imaging (fMRI) has become a broadly accepted presurgical mapping tool for pediatric populations with brain pathology. The aim of this article is to provide general guidelines on the pragmatic aspects of performing and processing fMRI, as well as interpreting its results across children of all age groups. Based on the author's accumulated experience of more than 20 years on this specific field, these guidelines consider many factors that include the particular physiology and anatomy of the child's brain, and how specific peculiarities may pose disadvantages or even certain advantages when performing fMRI procedures. The author carefully details the various challenges that the practitioner might face in dealing with limited volitional behavior and language comprehension of infants and small children and remedial strategies. The type and proper choice of task-based paradigms in keeping with the age and performance of the patient are discussed, as well as the appropriate selection and dosage of sedative agents and their inherent limitations. Recommendations about the scanner and settings for specific sequences are provided, as well as the required devices for appropriate stimulus delivery, response, and motion control. Practical aspects of fMRI postprocessing and quality control are discussed. Finally, given the relevance of resting-state-fMRI for use in noncooperative patients, a praxis-oriented guide to obtain, classify, and understand the spontaneous neural networks (utilizing independent component analysis) is also provided. The article concludes with a thorough discussion about the possible pitfalls at different stages of the fMRI process.

Nomograms to Predict Verbal Memory Decline After Temporal Lobe Resection in Adults With Epilepsy

OBJECTIVE

To develop and externally validate models to predict the probability of postoperative verbal memory decline in adults after temporal lobe resection (TLR) for epilepsy using easily accessible preoperative clinical predictors.

METHODS

Multivariable models were developed to predict delayed verbal memory outcome on 3 commonly used measures: Rey Auditory Verbal Learning Test (RAVLT) and Logical Memory (LM) and Verbal Paired Associates (VPA) subtests from Wechsler Memory Scale-Third Edition. With the use of the Harrell step-down procedure for variable selection, models were developed in 359 adults who underwent TLR at the Cleveland Clinic and validated in 290 adults at 1 of 5 epilepsy surgery centers in the United States or Canada.

RESULTS

Twenty-nine percent of the development cohort and 26% of the validation cohort demonstrated significant decline on at least 1 verbal memory measure. Initial models had good to excellent predictive accuracy (calibration [c] statistic range 0.77-0.80) in identifying patients with memory decline; however, models slightly underestimated decline in the validation cohort. Model coefficients were updated with data from both cohorts to improve stability. The model for RAVLT included surgery side, baseline memory score, and hippocampal resection. The models for LM and VPA included surgery side, baseline score, and education. Updated model performance was good to excellent (RAVLT c = 0.81, LM c = 0.76, VPA c = 0.78). Model calibration was very good, indicating no systematic overestimation or underestimation of risk.

CONCLUSIONS

Nomograms are provided in 2 easy-to-use formats to assist clinicians in estimating the probability of verbal memory decline in adults considering TLR for treatment of epilepsy.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that multivariable prediction models accurately predict verbal memory decline after TLR for epilepsy in adults.

Memory outcomes of temporal lobe surgery in adults aged over 45 years

OBJECTIVE

It is assumed that temporal lobe resection in older people is associated with worse seizure outcomes and potential postsurgical memory decline. We studied postsurgical memory development and surgical efficacy in patients over 45 years of age compared with younger patients.

METHODS

We studied 88 patients (51 male and 37 female) after temporal lobe surgery, which involved hippocampal resection. The patients were evaluated before surgery and in the first (72 patients) and/or third (57 patients) postsurgical year. The Wechsler Memory Scale III test was performed to evaluate the MQ postsurgical development. Engel's classification was used to evaluate the postsurgical seizure outcome.

RESULTS

The presurgical MQ (median 88) in ≥45 years age group was significantly lower than in both younger groups (median MQ = 100 for ≤30 years age group, p = 0.002; median MQ = 107 for 31-44 years age group, p = 0.002). Three years after the surgery, the MQ decreased significantly in ≤30 years age group (p = 0.012), while only non-significant MQ decline was observed in both older groups. We found no significant impact of age on the surgical outcome.

CONCLUSION

Higher age at the time of surgery does not significantly increase the risk for postsurgical memory decline; however, older patients are more likely to have lowered presurgical MQ. We did not find significant differences in the impact of surgery on seizure outcome among the age groups. Epilepsy surgery appears to be a safe and effective method in the age over 45 years even though an earlier surgery should be preferred.

Semantic and episodic memory in adults with temporal lobe epilepsy

The primary aims were to (1) identify the factor structure of tests thought to measure semantic and episodic memory and (2) examine whether patterns of impairment would show a double dissociation between these two memory systems at an individual level in patients with temporal lobe epilepsy (TLE). The secondary aim was to explore the impact of epilepsy-related variables on performance. This retrospective study involved a cohort of 54 adults who had been diagnosed with TLE and had undergone a neuropsychological assessment that included four memory tests traditionally used to measure either semantic memory (picture naming, animal fluency) or episodic memory (story recall, word list recall) at a single epilepsy surgery center in Australia. Principal component analysis revealed two factors albeit with unexpected loadings. Picture naming and story recall loaded on one factor. Animal fluency and word list recall loaded on another factor. There was no evidence of a double dissociation between semantic and episodic memory at an individual level. Left hemisphere seizure focus and early age of seizure onset related to worse performance on word list recall, picture naming and animal fluency, respectively. Our study highlights the importance of caution when interpreting the results of neuropsychological assessments, as not all putative tests of semantic and episodic memory may necessarily be measuring the same construct. Future directions for research are also considered.

Prevalence and factors of verbal learning and memory dysfunction in patients with epilepsy - A single centre study

The objective of this study is to determine prevalence and factors leading to verbal learning and memory dysfunction among patients with epilepsy. A total of 211 subjects were recruited. Their verbal memory was assessed by Rey's Auditory Verbal Learning Test (RAVLT). This test was further subdivided into four major spheres for analysis, namely the verbal learning, interference list, immediate memory and delayed memory. All data collected were analyzed using Statistical Package for Social Sciences. Among the 211 patients, 55% (n = 116) had focal seizures and the remaining 45% (n = 95) had generalized seizures. Prevalence of verbal learning and memory impairment was high at 39.97% overall, and found most commonly in patients with focal impaired awareness seizures. Verbal learning and immediate memory dysfunction were significantly lower in focal impaired awareness group compared to others. Age more than 50 years, exposure to three or more antiepileptic drugs and use of carbamazepine more than 1000 mg a day were the predictors in poor verbal memory outcome. No statistical difference was observed in the mean RAVLT scores among the gender and hand dominance groups. Between patients with and without electroencephalogram changes as well as brain magnetic resonance imaging changes, the mean RAVLT scores showed no statistically significant difference. Verbal learning and memory impairment is prevalent among the epilepsy patients. The consequences of the memory impairment can be as debilitating as the seizure control. RAVLT is a reliable and practical test in the clinical setting.

Verbal associative memory outcomes in pediatric surgical temporal lobe epilepsy: Exploring the impact of mesial structures

OBJECTIVE

We examined verbal associative memory outcomes in children with left- or right-sided temporal lobe epilepsy (TLE) who received combined lateral and mesial resections versus lateral resections sparing mesial structures. We hypothesized that children who underwent left-sided resections including mesial structures would show the greatest verbal associative memory declines following surgery.

METHOD

We retrospectively analyzed neuropsychology assessment results from a sample of 65 children with TLE who completed pre- and postoperative evaluation at the Hospital for Sick Children in Toronto, Canada. We examined verbal associative memory score changes between groups by laterality (left versus right) and resection type (lateral only versus lateral and mesial resection). We also explored potential associations between certain epilepsy-related characteristics and verbal associative memory changes.

RESULTS

Postoperative decline was found in children with left-sided resections, but not those with right-sided resections. In children who received left-sided resections, there was some suggestion of verbal associative memory decline in those who had both lateral and mesial tissues excised, but not in those with lateral resections only. Notably, there was also a language dominance (typical versus atypical) by resection type interaction. Specifically, for the typical language group, children with left lateral plus mesial resections (but not mesial sparing resections) showed postoperative verbal associative memory declines, whereas the opposite was true for the atypical language group.

SIGNIFICANCE

These data contribute to our growing understanding of verbal memory outcomes following TLE in childhood, with consideration of the extent of resection to mesial structures. Our findings also highlight the importance of language laterality when interpreting neuropsychological assessment findings and making predictions regarding risk of functional loss following surgery.

Standardization of an Arabic-Language Neuropsychological Battery for Epilepsy Surgical Evaluations

OBJECTIVES

This study provides a standardized Arabic language neuropsychological test battery and tests its ability to distinguish patients with left and right hemisphere epileptic foci who are candidates for surgical resection.

METHODS

An Arabic language battery of 15 tests was developed based on the neuropsychological test battery used at the Johns Hopkins Hospital for surgical evaluation of patients undergoing temporal lobe resection. With modifications where culturally required, 11 tests were translated to Arabic by the principal investigator and back-translated by two bilingual health professionals; four tests were available in Arabic and added to the battery. The battery was administered to 21 Arabic-speaking patients with left temporal epileptic foci, 21 with right temporal epileptic foci, and 46 neurologically and psychiatrically healthy adults.

RESULTS

Nearly all the Arabic test versions were capable of differentiating healthy controls and the temporal lobe epilepsy (TLE) groups. Tests known to distinguish left and right temporal lobectomy candidates, such as wordlist memory and prose recall, were able to do so as accurately as the English versions. Also, a roughly "culturally free" task (the Baltimore Board) and a newly developed version of the Boston Naming Test demonstrated some sensitivity to left temporal lobe involvement.

CONCLUSIONS

Arabic-language neuropsychological tests for epilepsy surgical evaluations are made available, demonstrate cultural sensitivity and clinical validity, and require further psychometric property and normative research. (JINS, 2019, 25, 761-771).

Postoperative memory prognosis in temporal lobe epilepsy surgery: The contribution of postictal memory

OBJECTIVE

The prediction of verbal memory decline after temporal lobe epilepsy (TLE) surgery remains difficult at an individual level. We evaluated the prognostic value of postictal memory testing in predicting the postoperative verbal memory function.

METHODS

Sixty-three consecutive patients were included in the analysis who underwent TLE surgery at our center with preoperative interictal/postictal and postoperative memory testing. Verbal memory was evaluated using the Rey Auditory Verbal Learning Test (RAVLT). We used reliable change indices with 90% confidence interval (90% RCIs) to evaluate a significant postoperative memory decline. The sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), area under the curve (AUC), and accuracy (ACC) were calculated. The analysis was performed for all TLE patients and for the subgroup with hippocampal sclerosis (HS).

RESULTS

Left-TLE patients (n = 31) had lower verbal memory scores on RAVLT than right-TLE at 3 months (57% vs 78%) and 12 months (53% vs 78%) after surgery. The 90% RCI was estimated to be a loss of 4 out of 15 items. The predictive value was Sn = 42%, Sp = 84%, PPV = 39%, NPV = 86%, AUC = 0.630, and ACC = 76% to predict a verbal memory decline in the whole group (n = 63). In HS patients (n = 41), the postictal verbal memory test had Sn = 50%, Sp = 88%, PPV = 50%, NPV = 88%, AUC = 0.689, and ACC = 81% to predict a significant postoperative decline.

SIGNIFICANCE

Postictal memory is a noninvasive bedside memory test that can help predict the postoperative verbal memory decline in patients with HS with an overall accuracy of 81%.

Temporal lobe epilepsy is associated with distinct cognitive phenotypes

Neuropsychological assessment is critical for understanding the impact of seizures on cognition and informing treatment decisions. While focus is often placed on examining groups based on seizure type/epilepsy syndrome, an alternate approach emphasizes empirically derived groups based solely on cognitive performance. This approach has been used to identify cognitive phenotypes in temporal lobe epilepsy (TLE). The current study sought to replicate prior work by Hermann and colleagues (2007) and identify cognitive phenotypes in a separate, larger cohort of 185 patients with TLE (92 left TLE, 93 right TLE). Cluster analysis revealed 3- and 4-cluster solutions, with clusters differentiated primarily by overall level of performance in the 3-cluster solution (Low, Middle, and High performance) and by more varying cognitive phenotypes in the 4-cluster solution (Globally Low, Low Executive Functioning/Speed, Low Language/Memory, and Globally High). Differences in cognitive performance as well as demographic and clinical seizure variables are presented. A greater proportion of the patients with left TLE were captured by Cluster 3 (Low Language/Memory) than by the other 3 clusters, though this cluster captured only approximately one-third of the overall group with left TLE. Consistent with prior findings, executive functioning and speed emerged as additional domains of interest in this sample of patients with TLE. The current results extend prior work examining cognitive phenotypes in TLE and highlight the importance of identifying the comprehensive range of potential cognitive profiles in TLE.

Imaging episodic memory during development and childhood epilepsy

Epilepsy affects 2.2 million adults in the USA, with 1 in 26 people developing epilepsy at some point in their lives. Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy as medial structures, and the hippocampus in particular, are prone to generating seizures. Selective anterior temporal resection (which removes the hippocampus) is the most effective intractable TLE treatment, but given the critical role of the mesial temporal lobe in memory functioning, resection can have negative effects on this crucial cognitive skill. To minimize the adverse impact of temporal lobe surgery on memory functioning, reliable pre-surgical guides are needed. Clinical functional magnetic resonance imaging (fMRI) provides reliable, noninvasive guidance of language functioning and plays a growing role in the pre-surgical evaluation for epilepsy patients; however, localization of memory function in children with epilepsy using fMRI has not been established. Aside from the lack of neuroimaging memory studies in children with TLE, studies of typical development are limited. This review will focus on the functional anatomy of memory systems throughout development, with a focus on TLE. TLE provides the ideal model from which to understand memory function and the limits of plasticity and compensation/reorganization throughout development.

Brain network alterations of mesial temporal lobe epilepsy with cognitive dysfunction following anterior temporal lobectomy

The aims of this study were to investigate the brain network connectivity alterations of intractable unilateral mesial temporal lobe epilepsy (MTLE) with cognitive dysfunction before and after anterior temporal lobectomy (ATL) using resting-state functional magnetic resonance imaging (rs-fMRI) study and to further observe the correlation between the brain network connectivity with cognitive performance. Fourteen patients with unilateral left MTLE before and after ATL were compared with thirty healthy controls (HCs) on functional connectivity (FC) between resting-state networks (RSNs). The correlation between the neuropsychological tests of patients and abnormal FC was further investigated. When compared with the HCs, patients before surgery showed significantly changed FC between special RSNs. No difference of FC was found between each RSN when patients were compared with the HCs after surgery. Compared with patients before surgery, patients after surgery showed significantly decreased FC between RSNs. Abnormal FC between RSNs significantly correlated with Montreal Cognitive Assessment (MoCA) scores. Our study suggested that dynamic alterations of RSN after ATL in unilateral MTLE may be closely related with seizure generating. However, unchanged FC between RSN before and after ATL may be closely related with cognitive performance. The present findings may help us understand the feature of brain network alterations in patients with left MTLE who became seizure-free following ATL.

Correlation of neuropsychological and metabolic changes after epilepsy surgery in patients with left mesial temporal lobe epilepsy with hippocampal sclerosis

Background

Epilepsy surgery often causes changes in cognition and cerebral glucose metabolism. Our aim was to explore relationships between pre- and postoperative cerebral metabolism as measured with ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) and neuropsychological test scores in patients with left mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), who were rendered seizure-free after epilepsy surgery.

Results

Thirteen patients were included. All had neuropsychological testing and an interictal FDG-PET scan of the brain pre- and postoperative. Correlations between changes in neuropsychological test scores and metabolism were examined using statistical parametric mapping (SPM). There were no significant changes in the neuropsychological test scores pre- and postoperatively at the group level. Decreased metabolism was observed in the left mesial temporal regions and occipital lobe. Increased metabolism was observed in the bi-frontal and right parietal lobes, temporal lobes, occipital lobes, thalamus, cerebellum, and vermis. In these regions, we did not find a correlation between changes in metabolism and neuropsychological test scores. A significant negative correlation, however, was found between metabolic changes in the precuneus and Boston Naming Test (BNT) scores.

Conclusions

There are significant metabolic decreases in the left mesial temporal regions and increases in the bi-frontal lobes; right parietal, temporal, and occipital lobes; right thalamus; cerebellum; and vermis in patients with left MTLE-HS who were rendered seizure-free after epilepsy surgery. We could not confirm that these changes translate into significant cognitive changes. A significant negative correlation was found between changes in confrontation naming and changes in metabolism in the precuneus. We speculate that the precuneus may play a compensatory role in patients with postoperative naming difficulties after left TLE surgery. Understanding of these neural mechanisms may aid in designing cognitive rehabilitation strategies.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0385-5) contains supplementary material, which is available to authorized users.

Verbal memory decline from hippocampal depth electrodes in temporal lobe surgery for epilepsy

OBJECTIVE

To explore whether patients with refractory mesial temporal lobe epilepsy risk aggravated verbal memory loss from intracranial electroencephalography (EEG) recording with longitudinal hippocampal electrodes in the language-dominant hemisphere.

METHODS

A long-term neuropsychological follow-up (mean 61.5 months, range 22-111 months) was performed in 40 patients after ictal registration with left hippocampal depth electrodes (study group, n = 16) or no invasive EEG, only extracranial registration (reference group, n = 24). The groups were equal with respect to education, age at seizure onset, epilepsy duration, and prevalence of pharmacoresistant temporal lobe epilepsy (TLE; 75%) versus seizure freedom (25%). Retrospective neuropsychological data from preoperative surgical workup (T1) and prospective follow-up neuropsychological data (T2) were compared. A ≥1 SD intrapatient decline was considered as clinically relevant deterioration of verbal memory.

RESULTS

Significant decline in verbal memory was seen in 56% of the patients in the study group compared to 21% in the reference group. At T1, there were no statistical between-group differences in memory performance. At T2, between-group comparison showed significantly greater verbal memory decline for the study group (Claeson Dahl Learning and Retention Test, Verbal Learning: p = 0.05; Rey Auditory Verbal Learning Test, Total Learning: p = 0.04; Claeson Dahl Learning and Retention Test, Verbal Retention: p = 0.04). An odds ratio (OR) of 7.1 (90% confidence interval [CI] 1.3-37.7) for verbal memory decline was seen if right temporal lobe resection (R TLR) had been performed between T1 and T2. The difference between groups remained unchanged when patients who had undergone R TLR were excluded from the analysis, with a remaining aggravated significant decline in verbal memory performance for the study group compared to the reference group.

SIGNIFICANCE

Our results suggest a risk of verbal memory deterioration after the use of depth electrodes along the longitudinal axis of the hippocampus. Until this issue is further investigated, caution regarding depth electrodes in the language-dominant hemisphere hippocampus seems advisable.

A Functional MRI-Based Model for Individual Memory Assessment in Patients Eligible for Anterior Temporal Lobe Resection

Title:

A functional (f) MRI-based model for individual memory assessment in patients eligible for temporal lobe resection.

Aim:

To investigate if pre-operative fMRI memory paradigms, add predictive information with regard to post-surgical memory deficits.

Methods:

Fourteen pharmacoresistant Temporal Lobe Epilepsy (TLE) patients accepted for Anterior Temporal Lobe Resection (ATLR) were included. A clinical risk assessment score (RAS 0-3) was constructed from structural MRI, neuropsychological testing and hemisphere dominance. fMRI lateralization indices (LIs) over frontal language and medial temporal regions were calculated. Predictive value from clinical risk scoring and added value from fMRI LIs were correlated to post-surgical memory change scores (significant decline -1 SD). Verbal memory outcome was classified either as expected (RAS 2-3 and post-operative decline; RAS 0-1 and intact post-operative verbal memory) or as unexpected (RAS 2-3 and intact post-operative verbal memory post-surgery; RAS 0-1 and post-operative decline).

Results:

RAS for verbal memory decline exhibited a specificity of 67% and a sensitivity of 75%. Significant correlations were found between frontal language LIs and post-operative verbal memory (r = -0.802; p = 0.017) for left (L) TLE and between medial temporal lobe LIs and visuospatial memory (r = 0.829; p = 0.021), as well as verbal memory (r = 0.714; p = 0.055) for right (R) TLE. Ten patients had expected outcome and four patients had an unexpected outcome. In two MRI-negative RTLE patients that suffered significant verbal memory decline post-operatively, fMRI identified bilateral language and right lateralized medial temporal verbal encoding. In two LTLE patients with MRI pathology and verbal memory dysfunction, neither RAS nor fMRI identified the risk for aggravated verbal memory decline following ATLR.

Conclusion:

fMRI visualization of temporal-frontal network activation may add value to the pre-surgical work-up in epilepsy patients eligible for ATLR. Frontal language patterns are important for prediction in both L and RTLE. Strong left lateralized language in LTLE, as well as bilateral language combined with right lateralized encoding in RTLE, seems to indicate an increased risk for post-operative verbal memory decline.

Verbal memory after temporal lobe epilepsy surgery in children: Do only mesial structures matter?

OBJECTIVE

Previous findings have been mixed regarding verbal memory outcome after left temporal lobectomy in children, and there are few studies comparing verbal memory change after lateral versus mesial temporal lobe resections. We compared verbal memory outcome associated with sparing or including the mesial structures in children who underwent left or right temporal lobe resection. We also investigated predictors of postsurgical verbal memory change.

METHODS

We retrospectively assessed verbal memory change approximately 1 year after unilateral temporal lobe epilepsy surgery using a list learning task. Participants included 23 children who underwent temporal lobe surgery with sparing of the mesial structures (13 left), and 40 children who had a temporal lobectomy that included resection of mesial structures (22 left).

RESULTS

Children who underwent resection from the left lateral and mesial temporal lobe were the only group to show decline in verbal memory. Furthermore, when we considered language representation in the left temporal resection group, patients with left language representation and spared mesial structures showed essentially no change in verbal memory from preoperative to follow-up, whereas those with left language representation and excised mesial structures showed a decline. Postoperative seizure status had no effect on verbal memory change in children after left temporal lobe surgery. Finally, we found that patients with intact preoperative verbal memory experienced a significant decline compared to those with below average preoperative verbal memory.

SIGNIFICANCE

Our findings provide evidence of significant risk factors for verbal memory decline in children, specific to left mesial temporal lobe epilepsy. Children who undergo left temporal lobe surgery that includes mesial structures may be most vulnerable for verbal memory decline, especially when language representation is localized to the left hemisphere and when preoperative verbal memory is intact.

Parahippocampal and Entorhinal Resection Extent Predicts Verbal Memory Decline in an Epilepsy Surgery Cohort

The differential contribution of medial-temporal lobe regions to verbal declarative memory is debated within the neuroscience, neuropsychology, and cognitive psychology communities. We evaluate whether the extent of surgical resection within medial-temporal regions predicts longitudinal verbal learning and memory outcomes. This single-center retrospective observational study involved patients with refractory temporal lobe epilepsy undergoing unilateral anterior temporal lobe resection from 2007 to 2015. Thirty-two participants with Engel Class 1 and 2 outcomes were included (14 left, 18 right) and followed for a mean of 2.3 years after surgery (±1.5 years). Participants had baseline and postsurgical neuropsychological testing and high-resolution T1-weighted MRI scans. Postsurgical lesions were manually traced and coregistered to presurgical scans to precisely quantify resection extent of medial-temporal regions. Verbal learning and memory change scores were regressed on hippocampal, entorhinal, and parahippocampal resection volume after accounting for baseline performance. Overall, there were no significant differences in learning and memory change between patients who received left and right anterior temporal lobe resection. After controlling for baseline performance, the extent of left parahippocampal resection accounted for 27% (p = .021) of the variance in verbal short delay free recall. The extent of left entorhinal resection accounted for 37% (p = .004) of the variance in verbal short delay free recall. Our findings highlight the critical role that the left parahippocampal and entorhinal regions play in recall for verbal material.

Electrical stimulation of the parahippocampal gyrus for prediction of posthippocampectomy verbal memory decline

OBJECTIVE Epilepsy surgery is of known benefit for drug-resistant temporal lobe epilepsy (TLE); however, a certain number of patients suffer significant decline in verbal memory after hippocampectomy. To prevent this disabling complication, a reliable test for predicting postoperative memory decline is greatly desired. Therefore, the authors assessed the value of electrical stimulation of the parahippocampal gyrus (PHG) as a provocation test of verbal memory decline after hippocampectomy on the dominant side. METHODS Eleven right-handed, Japanese-speaking patients with medically intractable left TLE participated in the study. Before surgery, they underwent provocative testing via electrical stimulation of the left PHG during a verbal encoding task. Their pre- and posthippocampectomy memory function was evaluated according to the Wechsler Memory Scale-Revised (WMS-R) and/or Mini-Mental State Examination (MMSE) before and 6 months after surgery. The relationship between postsurgical memory decline and results of the provocative test was evaluated. RESULTS Left hippocampectomy was performed in 7 of the 11 patients. In 3 patients with a positive provocative recognition test, verbal memory function, as assessed by the WMS-R, decreased after hippocampectomy, whereas in 4 patients with a negative provocative recognition test, verbal memory function, as assessed by the WMS-R or MMSE, was preserved. CONCLUSIONS Results of the present study suggest that electrical stimulation of the PHG is a reliable provocative test to predict posthippocampectomy verbal memory decline.

Declarative long-term memory and the mesial temporal lobe: Insights from a 5-year postsurgery follow-up study on refractory temporal lobe epilepsy

It is largely recognized that the mesial temporal lobe and its substructure support declarative long-term memory (LTM). So far, different theories have been suggested, and the organization of declarative verbal LTM in the brain is still a matter of debate. In the current study, we retrospectively selected 151 right-handed patients with temporal lobe epilepsy with and without hippocampal sclerosis, with a homogeneous (seizure-free) clinical outcome. We analyzed verbal memory performance within a normalized scores context, by means of prose recall and word paired-associate learning tasks. Patients were tested at presurgical baseline, 6months, 2 and 5years after anteromesial temporal lobe surgery, using parallel versions of the neuropsychological tests. Our main finding revealed a key involvement of the left temporal lobe and, in particular, of the left hippocampus in prose recall rather than word paired-associate task. We also confirmed that shorter duration of epilepsy, younger age, and withdrawal of antiepileptic drugs would predict a better memory outcome. When individual memory performance was taken into account, data showed that females affected by left temporal lobe epilepsy for longer duration were more at risk of presenting a clinically pathologic LTM at 5years after surgery. Taken together, these findings shed new light on verbal declarative memory in the mesial temporal lobe and on the behavioral signature of the functional reorganization after the surgical treatment of temporal lobe epilepsy.

Different effects of anterior temporal lobectomy and selective amygdalohippocampectomy on verbal memory performance of patients with epilepsy

The advantage of selective amygdalohippocampectomy (SAH) over anterior temporal lobectomy (ATL) for the treatment of temporal lobe epilepsy (TLE) remains controversial. Because ATL is more extensive and involves the lateral and medial parts of the temporal lobe, it may be predicted that its impact on memory is more important than SAH, which involves resection of medial temporal structures only. However, several studies do not support this assumption. Possible explanations include task-specific factors such as the extent of semantic and syntactic information to be memorized and failure to control for main confounders. We compared preoperative vs. postoperative memory performance in 13 patients with SAH with 26 patients who underwent ATL matched on side of surgery, IQ, age at seizure onset, and age at surgery. Memory function was assessed using the Logical Memory subtest from the Wechsler Memory Scales - 3rd edition (LM-WMS), the Rey Auditory Verbal Learning Test (RAVLT), the Digit Span subtest from the Wechsler Adult Intelligence Scale, and the Rey-Osterrieth Complex Figure Test. Repeated measures analyses of variance revealed opposite effects of SAH and ATL on the two verbal learning memory tests. On the immediate recall trial of the LM-WMS, performance deteriorated after ATL in comparison with that after SAH. By contrast, on the delayed recognition trial of the RAVLT, performance deteriorated after SAH compared with that after ATL. However, additional analyses revealed that the latter finding was only observed when surgery was conducted in the right hemisphere. No interaction effects were found on other memory outcomes. The results are congruent with the view that tasks involving rich semantic content and syntactical structure are more sensitive to the effects of lateral temporal cortex resection as compared with mesiotemporal resection. The findings highlight the importance of task selection in the assessment of memory in patients undergoing TLE surgery.

Functional and structural correlates of memory in patients with mesial temporal lobe epilepsy

Individuals with medial temporal lobe epilepsy (mTLE) often show material-specific memory impairment (verbal for left, visuospatial for right hemisphere), which can be exacerbated following surgery aimed at the epileptogenic regions of medial and anterolateral temporal cortex. There is a growing body of evidence suggesting that characterization of structural and functional integrity of these regions using MRI can aid in prediction of post-surgical risk of further memory decline. We investigated the nature of the relationship between structural and functional indices of hippocampal integrity with pre-operative memory performance in a group of 26 patients with unilateral mTLE. Structural integrity was assessed using hippocampal volumes, while functional integrity was assessed using hippocampal activation during the encoding of novel scenes. We quantified structural and functional integrity in terms of asymmetry, calculated as (L - R)/(L + R). Factor scores for verbal and visual memory were calculated from a clinical database and an asymmetry score (verbal - visual) was used to characterize memory performance. We found, as expected, a significant difference between left and right mTLE (RTLE) groups for hippocampal volume asymmetry, with each group showing an asymmetry favoring the unaffected temporal lobe. Encoding activation asymmetry showed a similar pattern, with left mTLE patients showing activation preferential to the right hemisphere and RTLE patients showing the reverse. Finally, we demonstrated that functional integrity mediated the relationship between structural integrity and memory performance for memory asymmetry, suggesting that even if structural changes are evident, ultimately it is the functional integrity of the tissue that most closely explains behavioral performance.

Weighing the value of memory loss in the surgical evaluation of left temporal lobe epilepsy: a decision analysis

OBJECTIVES

Anterior temporal lobectomy is curative for many patients with disabling medically refractory temporal lobe epilepsy, but carries an inherent risk of disabling verbal memory loss. Although accurate prediction of iatrogenic memory loss is becoming increasingly possible, it remains unclear how much weight such predictions should have in surgical decision making. Here we aim to create a framework that facilitates a systematic and integrated assessment of the relative risks and benefits of surgery versus medical management for patients with left temporal lobe epilepsy.

METHODS

We constructed a Markov decision model to evaluate the probabilistic outcomes and associated health utilities associated with choosing to undergo a left anterior temporal lobectomy versus continuing with medical management for patients with medically refractory left temporal lobe epilepsy. Three base-cases were considered, representing a spectrum of surgical candidates encountered in practice, with varying degrees of epilepsy-related disability and potential for decreased quality of life in response to post-surgical verbal memory deficits.

RESULTS

For patients with moderately severe seizures and moderate risk of verbal memory loss, medical management was the preferred decision, with increased quality-adjusted life expectancy. However, the preferred choice was sensitive to clinically meaningful changes in several parameters, including quality of life impact of verbal memory decline, quality of life with seizures, mortality rate with medical management, probability of remission following surgery, and probability of remission with medical management.

SIGNIFICANCE

Our decision model suggests that for patients with left temporal lobe epilepsy, quantitative assessment of risk and benefit should guide recommendation of therapy. In particular, risk for and potential impact of verbal memory decline should be carefully weighed against the degree of disability conferred by continued seizures on a patient-by-patient basis.

Memory outcome one year after stereotactic interstitial radiosurgery in patients with epilepsy due to hypothalamic hamartomas

Epileptic seizures caused by hypothalamic hamartomas (HHs) are highly pharmacoresistant. Resective surgical approaches have shown some efficacy in controlling seizures; however, they bear a significant risk of postoperative mnemonic deterioration due to the close anatomical proximity of the HHs to structures essential for memory functions. We report on cognitive outcome in 26 patients with structural epilepsy due to HHs one year after interstitial radiosurgery. Individually, deteriorations occurred more frequently in declarative memory functions (in 20 to 50% of the patients), whereas more than 80% of the patients revealed stable or even improved performance in attentional functions. Preoperative better memory functions were associated with higher risk of postoperative performance decline. After radiosurgery, half of the patients showed more than 50%, and some up to 90%, of seizure reduction. Hypothalamic hamartoma volumes were significantly reduced at follow-up. Transient radiogenic edema found in 10/26 patients was not associated with further cognitive decline after radiosurgery. These results are highly relevant for therapeutic decisions and patient consultation on timing and choice of nonmedical treatment options for HHs.

Working memory network plasticity after anterior temporal lobe resection: a longitudinal functional magnetic resonance imaging study

Temporal lobe surgery can control seizures in drug-resistant epilepsy, but its impact on working memory is poorly understood. Using functional MRI, Stretton et al. reveal improvements in working memory post-surgery, which depend upon the functional capacity of the hippocampal remnant and the functional reserve of the contralateral hippocampus.

Working memory is a crucial cognitive function that is disrupted in temporal lobe epilepsy. It is unclear whether this impairment is a consequence of temporal lobe involvement in working memory processes or due to seizure spread to extratemporal eloquent cortex. Anterior temporal lobe resection controls seizures in 50–80% of patients with drug-resistant temporal lobe epilepsy and the effect of surgery on working memory are poorly understood both at a behavioural and neural level. We investigated the impact of temporal lobe resection on the efficiency and functional anatomy of working memory networks. We studied 33 patients with unilateral medial temporal lobe epilepsy (16 left) before, 3 and 12 months after anterior temporal lobe resection. Fifteen healthy control subjects were also assessed in parallel. All subjects had neuropsychological testing and performed a visuospatial working memory functional magnetic resonance imaging paradigm on these three separate occasions. Changes in activation and deactivation patterns were modelled individually and compared between groups. Changes in task performance were included as regressors of interest to assess the efficiency of changes in the networks. Left and right temporal lobe epilepsy patients were impaired on preoperative measures of working memory compared to controls. Working memory performance did not decline following left or right temporal lobe resection, but improved at 3 and 12 months following left and, to a lesser extent, following right anterior temporal lobe resection. After left anterior temporal lobe resection, improved performance correlated with greater deactivation of the left hippocampal remnant and the contralateral right hippocampus. There was a failure of increased deactivation of the left hippocampal remnant at 3 months after left temporal lobe resection compared to control subjects, which had normalized 12 months after surgery. Following right anterior temporal lobe resection there was a progressive increase of activation in the right superior parietal lobe at 3 and 12 months after surgery. There was greater deactivation of the right hippocampal remnant compared to controls between 3 and 12 months after right anterior temporal lobe resection that was associated with lesser improvement in task performance. Working memory improved after anterior temporal lobe resection, particularly following left-sided resections. Postoperative working memory was reliant on the functional capacity of the hippocampal remnant and, following left resections, the functional reserve of the right hippocampus. These data suggest that working memory following temporal lobe resection is dependent on the engagement of the posterior medial temporal lobes and eloquent cortex.

Why Bilateral Damage Is Worse than Unilateral Damage to the Brain

Human and animal lesion studies have shown that behavior can be catastrophically impaired after bilateral lesions but that unilateral damage often produces little or no effect, even controlling for lesion extent. This pattern is found across many different sensory, motor, and memory domains. Despite these findings, there has been no systematic, computational explanation. We found that the same striking difference between unilateral and bilateral damage emerged in a distributed, recurrent attractor neural network. The difference persists in simple feedforward networks, where it can be understood in explicit quantitative terms. In essence, damage both distorts and reduces the magnitude of relevant activity in each hemisphere. Unilateral damage reduces the relative magnitude of the contribution to performance of the damaged side, allowing the intact side to dominate performance. In contrast, balanced bilateral damage distorts representations on both sides, which contribute equally, resulting in degraded performance. The model's ability to account for relevant patient data suggests that mechanisms similar to those in the model may operate in the brain.

Verbal memory after epilepsy surgery in childhood

PURPOSE

To investigate verbal memory after epilepsy surgery both group-wise and at the level of individual children, and to assess associations with side of surgery and removal of the temporal lobe.

METHODS

A prospective controlled study in a consecutive sample of 21 children undergoing epilepsy surgery, with comprehensive assessments of verbal memory before surgery and six, 12 and 24 months after surgery. For each patient, two age- and gender-matched controls were tested at similar intervals. Standardized regression-based (SRB) analysis was applied to compare post-surgical change in individual patients with change in controls.

RESULTS

Group-wise, average normed scores on verbal memory tests were higher after epilepsy surgery than before, corroborating earlier reports. By dint of empirically based SRB analysis, however, considerable individual differences in post-surgical change were revealed. Children with resections that included the left temporal lobe functioned significantly poorer than predicted on the basis of their pre-surgical performance. In contrast, verbal memory performance after surgery was consistent with pre-surgical baseline in the majority of children with resections that spared the left temporal lobe.

CONCLUSIONS

Despite cessation of epileptic seizures, verbal memory remains vulnerable in children who required surgery including the left temporal lobe. In most - but not all - children with other types of surgery, post-surgical verbal memory is consistent with their individual pre-surgical base level.

Hemispheric lateralization interrupted: material-specific memory deficits in temporal lobe epilepsy

The hemispheric lateralization of memory has largely been informed through the study of patients with temporal lobe epilepsy originating from medial temporal sources (mTLE). The material-specific model of memory relies on the basic framework that the left temporal lobe mediates verbal memories, while the right temporal lobe mediates non-verbal memories. Over the years, this model has been refined, and even challenged, as our understanding of the material-specific memory deficits in mTLE has been further elaborated in the neuropsychological and neuroimaging literature. The first goal of this mini-review is to highlight the major findings in the mTLE literature that have advanced and expanded our understanding of material-specific memory deficits in mTLE. Second, we will review how functional neuroimaging patterns of material-specific hemispheric lateralization in mTLE are being translated into the innovative clinical application of preoperative fMRI memory mapping.

Famous face identification in temporal lobe epilepsy: support for a multimodal integration model of semantic memory

This study aims to demonstrate that the left and right anterior temporal lobes (ATLs) perform critical but unique roles in famous face identification, with damage to either leading to differing deficit patterns reflecting decreased access to lexical or semantic concepts but not their degradation. Famous face identification was studied in 22 presurgical and 14 postsurgical temporal lobe epilepsy (TLE) patients and 20 healthy comparison subjects using free recall and multiple choice (MC) paradigms. Right TLE patients exhibited presurgical deficits in famous face recognition, and postsurgical deficits in both famous face recognition and familiarity judgments. However, they did not exhibit any problems with naming before or after surgery. In contrast, left TLE patients demonstrated both pre- and postsurgical deficits in famous face naming but no significant deficits in recognition or familiarity. Double dissociations in performance between groups were alleviated by altering task demands. Postsurgical right TLE patients provided with MC options correctly identified greater than 70% of famous faces they initially rated as unfamiliar. Left TLE patients accurately chose the name for nearly all famous faces they recognized (based on their verbal description) but initially failed to name, although they tended to rapidly lose access to this name. We believe alterations in task demands activate alternative routes to semantic and lexical networks, demonstrating that unique pathways to such stored information exist, and suggesting a different role for each ATL in identifying visually presented famous faces. The right ATL appears to play a fundamental role in accessing semantic information from a visual route, with the left ATL serving to link semantic information to the language system to produce a specific name. These findings challenge several assumptions underlying amodal models of semantic memory, and provide support for the integrated multimodal theories of semantic memory and a distributed representation of concepts.