MRI hippocampal volumes and memory function before and after temporal lobectomy

Location-based selection of the surgical approach to preserve the hippocampus in lesion-associated temporal lobe epilepsy

BACKGROUND AND OBJECTIVES

Surgical resections for lesions associated with intractable temporal lobe epilepsy (TLE) offers good seizure outcomes.However, the necessity of hippocampectomy in addition to lesionectomy is controversial, especially when the hippocampus is not involved by the lesion. Lesionectomy alone, preserving the hippocampus by an appropriate surgical approach, might offer good seizure outcomes while maintaining neurocognitive function. In the present study, the aims were to examine the surgical strategy for lesions associated with TLE and to present how to select surgical approaches to preserve the hippocampus.

METHODS

A total of 22 consecutive lesion-associated TLE patients who underwent lesionectomy alone were retrospectively reviewed. The surgical approach, transsylvian, transorbital, subtemporal, supracerebellar transtentorial, or transcortical approach, was selected based on the location of the lesion. Postoperative seizure outcomes were classified by the Engel classification. Neurocognitive outcomes were assessed before and after surgery if possible. The pathology, the extent of resection, and lesion recurrence were reviewed.

RESULTS

The transsylvian approach was selected in six patients, the transorbital approach in one patient, the subtemporal approach in three patients, the supracerebellar transtentorial approach in five patients, and the transcortical approach in seven patients. Eighteen of 22 (81.8 %) patients achieved Engel's class I or II good seizure outcomes. No patients had neurocognitive deterioration after surgery. Twelve patients had various types of brain tumors, and ten patients had non-tumorous lesions. Gross total resection was achieved in 21 patients. All patients had no recurrence.

CONCLUSION

For patients with lesion-associated TLE, lesionectomy alone by the appropriate surgical approach offers satisfactory seizure outcomes while preserving hippocampus.

A Comprehensive Review of Recent Trends in Surgical Approaches for Epilepsy Management

Epilepsy is a neurological disorder that affects millions of people worldwide, with a significant proportion of patients experiencing drug-resistant epilepsy, where seizures remain uncontrolled despite medical treatment. This review evaluates the latest surgical techniques for managing epilepsy, focusing on their effectiveness, safety, and the ongoing challenges that hinder their broader adoption. We explored various databases including PubMed, Google Scholar, and Cochrane Library to look for relevant literature using the following keywords: Epilepsy, Resective Surgery, Corpus Collectumy, and Antiepileptic Drugs. A total of 54 relevant articles were found and thoroughly explored. Recent advancements in surgical interventions include resective procedures such as anterior temporal lobectomy, corpus callosotomy, and hemispherectomy, which have been particularly effective in reducing seizures for specific types of epilepsy. Minimally invasive techniques, including laser interstitial thermal therapy and focused ultrasound, are increasingly being used, offering promising outcomes for certain patient groups. Additionally, neuromodulation methods such as deep brain stimulation, vagus nerve stimulation, and responsive neurostimulation provide alternative treatment options, especially for patients who are not suitable candidates for resective surgery. Despite these advancements, the full potential of epilepsy surgery is often underutilized due to various challenges. Inconsistent referral practices, a lack of standardized surgical protocols, and significant socioeconomic barriers continue to limit access to these procedures. Addressing these issues through improved referral processes, better education for healthcare providers and patients, and ensuring equitable access to advanced surgical treatments is crucial for optimizing patient outcomes. Future research should focus on overcoming these barriers and assessing long-term outcomes to further enhance the care of patients with epilepsy.

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.

Interictal intracranial EEG asymmetry lateralizes temporal lobe epilepsy

Patients with drug-resistant temporal lobe epilepsy often undergo intracranial EEG recording to capture multiple seizures in order to lateralize the seizure onset zone. This process is associated with morbidity and often ends in postoperative seizure recurrence. Abundant interictal (between-seizure) data are captured during this process, but these data currently play a small role in surgical planning. Our objective was to predict the laterality of the seizure onset zone using interictal intracranial EEG data in patients with temporal lobe epilepsy. We performed a retrospective cohort study (single-centre study for model development; two-centre study for model validation). We studied patients with temporal lobe epilepsy undergoing intracranial EEG at the University of Pennsylvania (internal cohort) and the Medical University of South Carolina (external cohort) between 2015 and 2022. We developed a logistic regression model to predict seizure onset zone laterality using several interictal EEG features derived from recent publications. We compared the concordance between the model-predicted seizure onset zone laterality and the side of surgery between patients with good and poor surgical outcomes. Forty-seven patients (30 female; ages 20-69; 20 left-sided, 10 right-sided and 17 bilateral seizure onsets) were analysed for model development and internal validation. Nineteen patients (10 female; ages 23-73; 5 left-sided, 10 right-sided, 4 bilateral) were analysed for external validation. The internal cohort cross-validated area under the curve for a model trained using spike rates was 0.83 for a model predicting left-sided seizure onset and 0.68 for a model predicting right-sided seizure onset. Balanced accuracies in the external cohort were 79.3% and 78.9% for the left- and right-sided predictions, respectively. The predicted concordance between the laterality of the seizure onset zone and the side of surgery was higher in patients with good surgical outcome. We replicated the finding that right temporal lobe epilepsy was harder to distinguish in a separate modality of resting-state functional MRI. In conclusion, interictal EEG signatures are distinct across seizure onset zone lateralities. Left-sided seizure onsets are easier to distinguish than right-sided onsets. A model trained on spike rates accurately identifies patients with left-sided seizure onset zones and predicts surgical outcome. A potential clinical application of these findings could be to either support or oppose a hypothesis of unilateral temporal lobe epilepsy when deciding to pursue surgical resection or ablation as opposed to device implantation.

[Memory impairments in temporal lobe epilepsy]

Temporal lobe epilepsy is known to present with various cognitive impairments, among which memory deficits are frequently reported by patients. Memory deficits can be classified into two types: classical hippocampal amnesia, which is characterized by abnormalities detected in neuropsychological assessments, and atypical memory deficits, such as accelerated long-term amnesia and autobiographical memory impairment, which cannot be identified using standard testing methods. These deficits are believed to arise from a complex interplay among structural brain abnormalities, interictal epileptic discharges, pharmacological factors, and psychological states. While fundamental treatments are limited, there are opportunities for interventions such as environmental adjustments and rehabilitation. This review article aims to provide a comprehensive overview of the types, underlying pathophysiology, and intervention methods for memory disorders observed in patients with temporal lobe epilepsy.

Interictal intracranial EEG asymmetry lateralizes temporal lobe epilepsy

Patients with drug-resistant temporal lobe epilepsy often undergo intracranial EEG recording to capture multiple seizures in order to lateralize the seizure onset zone. This process is associated with morbidity and often ends in postoperative seizure recurrence. Abundant interictal (between-seizure) data is captured during this process, but these data currently play a small role in surgical planning. Our objective was to predict the laterality of the seizure onset zone using interictal (between-seizure) intracranial EEG data in patients with temporal lobe epilepsy. We performed a retrospective cohort study (single-center study for model development; two-center study for model validation). We studied patients with temporal lobe epilepsy undergoing intracranial EEG at the University of Pennsylvania (internal cohort) and the Medical University of South Carolina (external cohort) between 2015 and 2022. We developed a logistic regression model to predict seizure onset zone laterality using interictal EEG. We compared the concordance between the model-predicted seizure onset zone laterality and the side of surgery between patients with good and poor surgical outcomes. 47 patients (30 women; ages 20-69; 20 left-sided, 10 right-sided, and 17 bilateral seizure onsets) were analyzed for model development and internal validation. 19 patients (10 women; ages 23-73; 5 left-sided, 10 right-sided, 4 bilateral) were analyzed for external validation. The internal cohort cross-validated area under the curve for a model trained using spike rates was 0.83 for a model predicting left-sided seizure onset and 0.68 for a model predicting right-sided seizure onset. Balanced accuracies in the external cohort were 79.3% and 78.9% for the left- and right-sided predictions, respectively. The predicted concordance between the laterality of the seizure onset zone and the side of surgery was higher in patients with good surgical outcome. In conclusion, interictal EEG signatures are distinct across seizure onset zone lateralities. Left-sided seizure onsets are easier to distinguish than right-sided onsets. A model trained on spike rates accurately identifies patients with left-sided seizure onset zones and predicts surgical outcome.

Intracranial Neurofeedback Modulating Neural Activity in the Mesial Temporal Lobe During Memory Encoding: A Pilot Study

Removal of the mesial temporal lobe (MTL) is an established surgical procedure that leads to seizure freedom in patients with intractable MTL epilepsy; however, it carries the potential risk of memory damage. Neurofeedback (NF), which regulates brain function by converting brain activity into perceptible information and providing feedback, has attracted considerable attention in recent years for its potential as a novel complementary treatment for many neurological disorders. However, no research has attempted to artificially reorganize memory functions by applying NF before resective surgery to preserve memory functions. Thus, this study aimed (1) to construct a memory NF system that used intracranial electrodes to feedback neural activity on the language-dominant side of the MTL during memory encoding and (2) to verify whether neural activity and memory function in the MTL change with NF training. Two intractable epilepsy patients with implanted intracranial electrodes underwent at least five sessions of memory NF training to increase the theta power in the MTL. There was an increase in theta power and a decrease in fast beta and gamma powers in one of the patients in the late stage of memory NF sessions. NF signals were not correlated with memory function. Despite its limitations as a pilot study, to our best knowledge, this study is the first to report that intracranial NF may modulate neural activity in the MTL, which is involved in memory encoding. The findings provide important insights into the future development of NF systems for the artificial reorganization of memory functions.

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.

Processing speed in temporal lobe epilepsy. A scoping review

BACKGROUND

Impaired processing speed (PS) can affect patients with temporal lobe epilepsy (TLE). However, it is usually considered a nonspecific clinical feature and is not measured, but this raises lexical and methodological problems. This review aims to evaluate the existing terminology and assessment methods of PS in patients with TLE.

METHODS

A scoping review was conducted based on the extended guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis. The electronic literature search was conducted on Medline-PubMed, American Psychological Association-PsycINFO, Elton Bryson Stephens Company, and Google Scholar, using the keywords "temporal lobe epilepsy" and "speed" or "slowing" plus "processing," "cognitive," "psychomotor," or "mental." Peer-reviewed articles published before December 2022 were analyzed if they were in English, including patients older than 14 years and at least one neuropsychological measure, reported original research focused on PS and had the selected keywords in the title, keywords, and abstract.

RESULTS

Seven articles published between December 2004 and September 2021 were selected. The terms "processing speed," "psychomotor speed," and "information processing speed," based on similar theoretical constructs, were the most frequently used. Assessment methods included non-computerized or paper-and-pencil tests (WAIS-III Digit Symbol and Symbol Search subtests, Purdue Pegboard and Grooved Pegboard Tests, Trail Making Test and Stroop Color-Word Test) and computerized tests (Sternberg Memory Scanning Test, Pattern Comparison Processing Speed, Computerized Visual Searching). In some studies, impairment was associated with white and gray matter damage in the brain, independent of clinical and treatment variables.

CONCLUSION

Clinical research on TLE has focused inconsistently on PS. Different evaluation terms and methods have been used while referring to similar theoretical constructs. These findings highlight a gap between the clinical importance of PS and its assessment. Studies are needed to share terms and tools among clinical centers and clarify the position of PS in the TLE phenotype.

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.

Optimal Surgical Extent for Memory and Seizure Outcome in Temporal Lobe Epilepsy

OBJECTIVE

Postoperative memory decline is an important consequence of anterior temporal lobe resection (ATLR) for temporal lobe epilepsy (TLE), and the extent of resection may be a modifiable factor. This study aimed to define optimal resection margins for cognitive outcome while maintaining a high rate of postoperative seizure freedom.

METHODS

This cohort study evaluated the resection extent on postoperative structural MRI using automated voxel-based methods and manual measurements in 142 consecutive patients with unilateral drug refractory TLE (74 left, 68 right TLE) who underwent standard ATLR.

RESULTS

Voxel-wise analyses revealed that postsurgical verbal memory decline correlated with resections of the posterior hippocampus and inferior temporal gyrus, whereas larger resections of the fusiform gyrus were associated with worsening of visual memory in left TLE. Limiting the posterior extent of left hippocampal resection to 55% reduced the odds of significant postoperative verbal memory decline by a factor of 8.1 (95% CI 1.5-44.4, p = 0.02). Seizure freedom was not related to posterior resection extent, but to the piriform cortex removal after left ATLR. In right TLE, variability of the posterior extent of resection was not associated with verbal and visual memory decline or seizures after surgery.

INTERPRETATION

The extent of surgical resection is an independent and modifiable risk factor for cognitive decline and seizures after left ATLR. Adapting the posterior extent of left ATLR might optimize postoperative outcome, with reduced risk of memory impairment while maintaining comparable seizure-freedom rates. The current, more lenient, approach might be appropriate for right ATLR. ANN NEUROL 2021.

New Horizons in Temporal Lobe Seizure Control

SUMMARY

In patients with mesial temporal lobe epilepsy, high-frequency, low-amplitude electrical stimulation (ES) was applied during 3 weeks through contacts of intracranial electrodes that defined the epileptogenic zone. This subacute ES induced cessation of spontaneous seizures, decreased the number of EEG interictal spikes, caused a 10-fold increase in threshold to induce postdischarges, and showed a profound decrease in regional blood flow of the stimulated area in SPECT studies. Autoradiography analysis of surgical specimens from these patients demonstrated increased expression of benzodiazepine receptors and in gamma-aminobutyric acid content, particularly in the parahippocampal cortex. These observations provided evidence of a gamma-aminobutyric acid-mediated antiepileptic effect induced by ES. Several reports of long-term hippocampal ES through internalized neurostimulators have confirmed the antiepileptic effect on mesial temporal lobe-initiated seizures, with preservation of neuropsychological performance, in particular memory functions. The experience of the authors is that the response is optimal in patients without hippocampal sclerosis evidenced by MRI, whereas it is less significant and delayed in patients with hippocampal sclerosis. Other studies reported the best result stimulating through the contacts in the subiculum, the transition between the hippocampus and parahippocampal cortex, that usually escapes to the hippocampal sclerosis. Currently, the effect of ES directed at the subiculum and the parahippocampal cortex in patients with hippocampal sclerosis is under investigation.

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.

Multiple hippocampal transections for mesial temporal lobe epilepsy

Background:

The purpose of this study was to evaluate the effectiveness of multiple hippocampal transections (MHT) in the treatment of drug-resistant mesial temporal lobe epilepsy.

Methods:

Six patients underwent MHT at Burdenko Neurosurgery Center in 2018. The age of the patients varied from 18 to 43 years. All patients suffered from refractory epilepsy caused by focal lesions of the mesial temporal complex or temporal pole in dominant side. Postoperative pathology revealed neuronal-glial tumors in two patients, focal cortical dysplasia (FCD) of the temporal pole – in two patients, cavernous angioma – in one patient, and encephalocele of the preuncal area – in one patient.

Results:

All patients underwent surgery satisfactorily. There were no postoperative complications except for homonymous superior quadrantanopia. This kind of visual field loss was noted in four cases out of six. During the follow-up period five patients out of six had Engel Class I outcome (83.3%). In one case, seizures developed after 1 month in a patient with FCD in the uncus (Engel IVA). After surgery, three out of six patients developed significant nominative aphasia. Two patients relative to the preoperative level demonstrated improvement in delayed verbal memory after MHT. Two patients showed a decrease level in delayed verbal memory. In preoperative period, visual memory was below the normal in one patient. Delayed visual memory in two cases impaired compared to the preoperative level.

Conclusion:

MHT can be considered as an effective method of drug-resistant mesial temporal lobe epilepsy caused by tumors of the medial temporal complex. At the same time, MHT makes it possible to preserve memory in patients with structurally preserved hippocampus. However, MHT do not guarantee the preservation of memory after surgery.

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.

Aging brain mechanics: Progress and promise of magnetic resonance elastography

Neuroimaging techniques that can sensitivity characterize healthy brain aging and detect subtle neuropathologies have enormous potential to assist in the early detection of neurodegenerative conditions such as Alzheimer's disease. Magnetic resonance elastography (MRE) has recently emerged as a reliable, high-resolution, and especially sensitive technique that can noninvasively characterize tissue biomechanical properties (i.e., viscoelasticity) in vivo in the living human brain. Brain tissue viscoelasticity provides a unique biophysical signature of neuroanatomy that are representative of the composition and organization of the complex tissue microstructure. In this article, we detail how progress in brain MRE technology has provided unique insights into healthy brain aging, neurodegeneration, and structure-function relationships. We further discuss additional promising technical innovations that will enhance the specificity and sensitivity for brain MRE to reveal considerably more about brain aging as well as its potentially valuable role as an imaging biomarker of neurodegeneration. MRE sensitivity may be particularly useful for assessing the efficacy of rehabilitation strategies, assisting in differentiating between dementia subtypes, and in understanding the causal mechanisms of disease which may lead to eventual pharmacotherapeutic development.

Critical area for memory decline after mesial temporal resection in epilepsy patients

OBJECTIVE

Mesial temporal lobe epilepsy (MTLE) surgery is associated with a risk of memory decline after surgery, but the effect of the extent and locus of temporal resection on postoperative memory function are controversial. The authors' aim in this study was to confirm if selective resection is effective in preserving memory function and identify critical areas for specific memory decline after temporal resection.

METHODS

In this single-center retrospective study, the authors investigated data from patients who underwent unilateral MTLE surgery between 2005 and 2015. Data from 74 MTLE patients (60.8% of whom were female; mean [SD] age at surgery 32 years [8.91 years] and duration of epilepsy 16 years [9.65 years]) with histologically proven hippocampal sclerosis were included. Forty-two patients underwent left-sided surgery. The resection area was manually delineated on each patient's postoperative T1-weighted images. Mapping was performed to see if the resected group, compared with the nonresected group, had worse postoperative memory in various memory domains, including verbal item, verbal associative, and figural memory.

RESULTS

Overall, 95.9% had a favorable epilepsy outcome. In verbal item memory, resection of the left lateral temporal area was related to postoperative decline in immediate and delayed recall scores of word lists. In verbal associative memory, resection of the anterior part of the left hippocampus, left parahippocampal area, and left lateral temporal area was related to postoperative decline in immediate recall scores of word pairs. Resection of the posterior part of the left hippocampus, left parahippocampal area, and left lateral temporal area was related to delayed recall scores of the same task. Similarly, in the figural memory, postoperative decline of immediate recall scores was associated with the resection of the anterior part of the right hippocampus, amygdala, parahippocampal area, and superior temporal area, and decline of delayed recall scores was related to resection of the posterior part of the right hippocampus and parahippocampal area.

CONCLUSIONS

Using voxel-based analysis, which accounts for the individual differences in the resection, the authors found a critical region for postoperative memory decline that is not revealed in the region-of-interest or groupwise comparison. Particularly, resection of the hippocampus was related to associative memory. In both verbal and visual memory, resection of the anterior part of the hippocampus was associated with immediate recall, and resection of the posterior part of the hippocampus was associated with delayed recall. Therefore, the authors' results suggest that selective resection may be effective in preserving postoperative memory decline.

Advances in the Surgical Management of Epilepsy: Drug-Resistant Focal Epilepsy in the Adult Patient

Pharmacoresistant seizures occur in nearly one-third of people with epilepsy. Medial temporal lobe and lesional epilepsy are the most favorable surgically remediable epileptic syndromes. Successful surgery may render the patient seizure-free, reduce antiseizure drug(s) adverse effects, improve quality of life, and decrease mortality. Surgical management should not be considered a procedure of "last resort." Despite the results of randomized controlled trials, surgery remains an underutilized treatment modality for patients with drug-resistant epilepsy (DRE). Important disparities affect patient referral and selection for surgical treatment. This article discusses the advances in surgical treatment of DRE in adults with focal seizures.

Network, clinical and sociodemographic features of cognitive phenotypes in temporal lobe epilepsy

This study explored the taxonomy of cognitive impairment within temporal lobe epilepsy and characterized the sociodemographic, clinical and neurobiological correlates of identified cognitive phenotypes. 111 temporal lobe epilepsy patients and 83 controls (mean ages 33 and 39, 57% and 61% female, respectively) from the Epilepsy Connectome Project underwent neuropsychological assessment, clinical interview, and high resolution 3T structural and resting-state functional MRI. A comprehensive neuropsychological test battery was reduced to core cognitive domains (language, memory, executive, visuospatial, motor speed) which were then subjected to cluster analysis. The resulting cognitive subgroups were compared in regard to sociodemographic and clinical epilepsy characteristics as well as variations in brain structure and functional connectivity. Three cognitive subgroups were identified (intact, language/memory/executive function impairment, generalized impairment) which differed significantly, in a systematic fashion, across multiple features. The generalized impairment group was characterized by an earlier age at medication initiation (P < 0.05), fewer patient (P < 0.001) and parental years of education (P < 0.05), greater racial diversity (P < 0.05), and greater number of lifetime generalized seizures (P < 0.001). The three groups also differed in an orderly manner across total intracranial (P < 0.001) and bilateral cerebellar cortex volumes (P < 0.01), and rate of bilateral hippocampal atrophy (P < 0.014), but minimally in regional measures of cortical volume or thickness. In contrast, large-scale patterns of cortical-subcortical covariance networks revealed significant differences across groups in global and local measures of community structure and distribution of hubs. Resting-state fMRI revealed stepwise anomalies as a function of cluster membership, with the most abnormal patterns of connectivity evident in the generalized impairment group and no significant differences from controls in the cognitively intact group. Overall, the distinct underlying cognitive phenotypes of temporal lobe epilepsy harbor systematic relationships with clinical, sociodemographic and neuroimaging correlates. Cognitive phenotype variations in patient and familial education and ethnicity, with linked variations in total intracranial volume, raise the question of an early and persisting socioeconomic-status related neurodevelopmental impact, with additional contributions of clinical epilepsy factors (e.g., lifetime generalized seizures). The neuroimaging features of cognitive phenotype membership are most notable for disrupted large scale cortical-subcortical networks and patterns of functional connectivity with bilateral hippocampal and cerebellar atrophy. The cognitive taxonomy of temporal lobe epilepsy appears influenced by features that reflect the combined influence of socioeconomic, neurodevelopmental and neurobiological risk factors.

Uncovering a Role for the Dorsal Hippocampal Commissure in Recognition Memory

The dorsal hippocampal commissure (DHC) is a white matter tract that provides interhemispheric connections between temporal lobe brain regions. Despite the importance of these regions for learning and memory, there is scant evidence of a role for the DHC in successful memory performance. We used diffusion-weighted magnetic resonance imaging (DW-MRI) and white matter tractography to reconstruct the DHC in both humans (in vivo) and nonhuman primates (ex vivo). Across species, our findings demonstrate a close consistency between the known anatomy and tract reconstructions of the DHC. Anterograde tract-tracer techniques also highlighted the parahippocampal origins of DHC fibers in nonhuman primates. Finally, we derived diffusion tensor MRI metrics from the DHC in a large sample of human subjects to investigate whether interindividual variation in DHC microstructure is predictive of memory performance. The mean diffusivity of the DHC correlated with performance in a standardized recognition memory task, an effect that was not reproduced in a comparison commissure tract-the anterior commissure. These findings highlight a potential role for the DHC in recognition memory, and our tract reconstruction approach has the potential to generate further novel insights into the role of this previously understudied white matter tract in both health and disease.

Effects of hippocampus-sparing resections in the temporal lobe: Hippocampal atrophy is associated with a decline in memory performance

OBJECTIVE

In patients with temporal lobe epilepsy (TLE) with a nonlesional and nonepileptogenic hippocampus (HC), in order to preserve functionally intact brain tissue, the HC is not resected. However, some patients experience postoperative memory decline, possibly due to disruption of the extrahippocampal memory network and secondary hippocampal volume (HV) loss. The purpose of this study was to determine the extent of hippocampal atrophy ipsilateral and contralateral to the side of the surgery and its relation to memory outcomes.

METHODS

Hippocampal volume and verbal as well as visual memory performance were retrospectively examined in 55 patients (mean age ± standard deviation [SD] 30 ± 15 years, 25 female, 31 left) before and 5 months after surgery within the temporal lobe that spared the entire HC. HV was extracted based on prespecified templates, and resection volumes were also determined.

RESULTS

HV loss was found both ipsilateral and contralateral to the side of surgery (P < .001). Postoperative left HV loss was a significant predictor of postoperative verbal memory deterioration after left-sided surgery (P < .01). Together with the preoperative verbal memory performance, postoperative left HV explained almost 60% of the variance (P < .0001). However, right HV was not a clear predictor of visual memory performance. Larger resection volumes were associated with smaller postoperative HV, irrespective of side of surgery (left: P < .05, right: P < .01).

SIGNIFICANCE

A disruption of the memory network by any resection within the TL, especially within the language-dominant hemisphere, may lead to HC atrophy and memory decline. These findings may further improve the counseling of patients concerning their postoperative memory outcome before TL resections sparing the entire HC.

Hippocampal viscoelasticity and episodic memory performance in healthy older adults examined with magnetic resonance elastography

Episodic memory is particularly sensitive to normative aging; however, studies investigating the structure-function relationships that support episodic memory have primarily been limited to gross volumetric measures of brain tissue health. Magnetic resonance elastography (MRE) is an emerging non-invasive, high-resolution imaging technique that uniquely quantifies brain viscoelasticity, and as such, provides a more specific measure of neural microstructural integrity. Recently, a significant double dissociation between orbitofrontal cortex-fluid intelligence and hippocampal-relational memory structure-function relationships was observed in young adults, highlighting the potential of sensitive MRE measures for studying brain health and its relation to cognitive function. However, the structure-function relationship observed by MRE has not yet been explored in healthy older adults. In this study, we examined the relationship between hippocampal (HC) viscoelasticity and episodic memory in cognitively healthy adults aged 66-73 years (N = 11), as measured with the verbal-paired associates (VPA) subtest from the Wechsler Memory Scale (WMS-R). Given the particular dependence of verbal memory tasks on the left HC, unilateral HC MRE measurements were considered for the first time. A significant negative correlation was found between left HC damping ratio, ξ and VPA recall score (r_s = -0.77, p = 0.009), which is consistent with previous findings of a relationship between HC ξ and memory performance in young adults. Conversely, correlations between right HC ξ with VPA recall score were not significant. These results highlight the utility of MRE to study cognitive decline and brain aging and suggest its possible use as a sensitive imaging biomarker for memory-related impairments.

Visuospatial learning and memory in children pre- and posttemporal lobe resection: Patterns of localization and lateralization

In children with epilepsy, the impact of surgery including or sparing the mesial temporal lobes (TLs) on visuospatial memory has not been thoroughly investigated, and a clear pattern of hemispheric lateralization has not been observed. The primary aim of this study was to examine visuospatial learning and memory outcomes in children with epilepsy prior to and one year after surgical excision, to determine whether outcomes differed as a function of the localization and lateralization of surgical excisions. Forty-six children who underwent unilateral TL surgery with sparing of the mesial structures (TL group, N = 21, 16 left) or including mesial structures (TL + M group, N = 25 children, 12 left) were retrospectively recruited. Outcomes on the Children's Memory Scale (CMS) Dot Locations subtest (learning, immediate, and delayed recall scores) were examined prior to and following epilepsy surgery. Results revealed significantly reduced visuospatial memory (delayed recall) in the TL + M compared with the TL group after surgery. Despite this significant postoperative difference, there was no significant change in learning, immediate, or delayed recall scores in either group. However, inspection of individual change scores showed that fewer children in the TL + M group improved in delayed recall after surgery (7.2%) compared with children in the TL group (30%) whereas a similar proportion of children in the TL + M (30.4%) and TL (23.3%) groups showed a decline. There were no significant differences in learning or memory scores as a function of seizure laterality before or after surgery and no differences in change over time. Seizure outcome, age at surgery, age at seizure onset, and percentage life with epilepsy were not related to visuospatial learning or memory outcomes; however, greater number of antiepileptic drugs (AEDs) following surgery was related to poorer visuospatial memory (delayed recall) in the TL + M group. In summary, the results show that visuospatial learning and memory performance do not seem to show a significant decline following TL resections in childhood, regardless of whether or not surgery includes the mesial TL and involves the left or right hemisphere. However, although mesial TL excisions might not result in a deficit in visuospatial memory, they may hinder progressions made after surgery. Further research is needed to examine how resection of the mesial TL (alone or in combination with lateral TL structures) affects visuospatial memory outcomes in children, as well as to investigate the degree to which other treatment factors, such as medication, may affect visual memory outcomes.

Clinically indicated electrical stimulation strategies to treat patients with medically refractory epilepsy

Focal epilepsies represent approximately half of all diagnoses, and more than one-third of these patients are refractory to pharmacologic treatment. Although resection can result in seizure freedom, many patients do not meet surgical criteria, as seizures may be multifocal in origin or have a focus in an eloquent region of the brain. For these individuals, several U.S. Food and Drug Administration (FDA)-approved electrical stimulation paradigms serve as alternative options, including vagus nerve stimulation, responsive neurostimulation, and stimulation of the anterior nucleus of the thalamus. All of these are safe, flexible, and lead to progressive seizure control over time when used as an adjunctive therapy to antiepileptic drugs. Focal epilepsies frequently involve significant comorbidities such as cognitive decline. Similar to antiepilepsy medications and surgical resection, current stimulation targets and parameters have yet to address cognitive impairments directly, with patients reporting persistent comorbidities associated with focal epilepsy despite a significant reduction in the number of their seizures. Although low-frequency theta oscillations of the septohippocampal network are critical for modulating cellular activity and, in turn, cognitive processing, the coordination of neural excitability is also imperative for preventing seizures. In this review, we summarize current FDA-approved electrical stimulation paradigms and propose that theta oscillations of the medial septal nucleus represent a novel neuromodulation target for concurrent seizure reduction and cognitive improvement in epilepsy. Ultimately, further advancements in clinical neurostimulation strategies will allow for the efficient treatment of both seizures and comorbidities, thereby improving overall quality of life for patients with epilepsy.

Temporal lobe asymmetry in FDG-PET uptake predicts neuropsychological and seizure outcomes after temporal lobectomy

OBJECTIVE

The objective of this study was to determine whether preoperative [¹⁸F]fludeoxyglucose (FDG)-positron emission tomography (PET) asymmetry in temporal lobe metabolism predicts neuropsychological and seizure outcomes after temporal lobectomy (TL).

METHODS

An archival sample of 47 adults with unilateral temporal lobe epilepsy who underwent TL of their language-dominant (29 left, 1 right) or nondominant (17 right) hemisphere were administered neuropsychological measures pre- and postoperatively. Post-TL seizure outcomes were measured at 1year. Regional FDG uptake values were defined by an automated technique, and a quantitative asymmetry index (AI) was calculated to represent the relative difference in the FDG uptake in the epileptic relative to the nonepileptic temporal lobe for four regions of interest: medial anterior temporal (MAT), lateral anterior temporal (LAT), medial posterior temporal (MPT), and lateral posterior temporal (LPT) cortices.

RESULTS

In language-dominant TL, naming outcomes were predicted by FDG uptake asymmetry in the MAT (r=-0.38) and LPT (r=-0.45) regions. For all patients, visual search and motor speed outcomes were predicted by FDG uptake asymmetry in all temporal regions (MPT, r=0.42; MAT, r=0.34; LPT, r=0.47; LAT, r=0.51). Seizure outcomes were predicted by FDG uptake asymmetry in the MAT (r=0.36) and MPT (r=0.30) regions. In all of these significant associations, greater hypometabolism in regions of the epileptic temporal lobe was associated with better postoperative outcomes.

CONCLUSIONS

Our results support the conclusion that FDG uptake asymmetry is a useful clinical tool in assessing risk for cognitive changes in patients being considered for TL.

Cognitive Outcome After Epilepsy Surgery in Children

Cognitive dysfunction in children with epilepsy is primarily contributed by etiology, seizures, frequency of interictal epileptiform discharges, and adverse effects of antiepileptic drugs. The direct effect of epilepsy surgery on cognitive outcome depends on two key factors: the function that is present in the epileptogenic zone to be removed, and the dysfunction outside the epileptogenic zone caused by epilepsy. Studies on cognitive outcome in children after various types of epilepsy surgery estimate "no significant change" in about 70% of children, improvement in cognition in 10%-15%, and decline in 10%-15%. In young children with epileptic encephalopathy, the reversible dysfunction outside the epileptogenic zone is larger and hence carry better chances of improved outcome after successful surgery. If the epileptogenic zone harbors significant cognitive function (memory, language, or other function), then a decline in function may occur with its resection. Understanding the pathophysiological basis for the cognitive changes after epilepsy surgery assists in counseling patients and families before surgery.

Paradigm Shifts in the Neuropsychology of Epilepsy

This article reviews the major paradigm shifts that have occurred in the area of the application of clinical and experimental neuropsychology to epilepsy and epilepsy surgery since the founding of the International Neuropsychological Society. The five paradigm shifts discussed include: 1) The neurobiology of cognitive disorders in epilepsy - expanding the landscape of syndrome-specific neuropsychological impairment; 2) pathways to comorbidities: bidirectional relationships and their clinical implications; 3) discovering quality of life: The concept, its quantification and applicability; 4) outcomes of epilepsy surgery: challenging conventional wisdom; and 5) Iatrogenic effects of treatment: cognitive and behavioral effects of antiepilepsy drugs. For each area we characterize the status of knowledge, the key developments that have occurred, and how they have altered our understanding of the epilepsies and their management. We conclude with a brief overview of where we believe the field will be headed in the next decade which includes changes in assessment paradigms, moving from characterization of comorbidities to interventions; increasing development of new measures, terminology and classification; increasing interest in neurodegenerative proteins; transitioning from clinical seizure features to modifiable risk factors; and neurobehavioral phenotypes. Overall, enormous progress has been made over the lifespan of the INS with promise of ongoing improvements in understanding of the cognitive and behavioral complications of the epilepsies and their treatment. (JINS, 2017, 23, 791-805).

A meta-analysis on progressive atrophy in intractable temporal lobe epilepsy: Time is brain?

OBJECTIVE

It remains unclear whether drug-resistant temporal lobe epilepsy (TLE) is associated with cumulative brain damage, with no expert consensus and no quantitative syntheses of the available evidence.

METHODS

We conducted a systematic review and meta-analysis of MRI studies on progressive atrophy, searching PubMed and Ovid MEDLINE databases for cross-sectional and longitudinal quantitative MRI studies on drug-resistant TLE.

RESULTS

We screened 2,976 records and assessed eligibility of 248 full-text articles. Forty-two articles met the inclusion criteria for quantitative evaluation. We observed a predominance of cross-sectional studies, use of different clinical indices of progression, and high heterogeneity in age-control procedures. Meta-analysis of 18/1 cross-sectional/longitudinal studies on hippocampal atrophy (n = 979 patients) yielded a pooled effect size of r = -0.42 for ipsilateral atrophy related to epilepsy duration (95% confidence interval [CI] -0.51 to -0.32; p < 0.0001; I² = 65.22%) and r = -0.35 related to seizure frequency (95% CI -0.47 to -0.22; p < 0.0001; I² = 61.97%). Sensitivity analyses did not change the results. Narrative synthesis of 25/3 cross-sectional/longitudinal studies on whole brain atrophy (n = 1,504 patients) indicated that >80% of articles reported duration-related progression in extratemporal cortical and subcortical regions. Detailed analysis of study design features yielded low to moderate levels of evidence for progressive atrophy across studies, mainly due to dominance of cross-sectional over longitudinal investigations, use of diverse measures of seizure estimates, and absence of consistent age control procedures.

CONCLUSIONS

While the neuroimaging literature is overall suggestive of progressive atrophy in drug-resistant TLE, published studies have employed rather weak designs to directly demonstrate it. Longitudinal multicohort studies are needed to unequivocally differentiate aging from disease progression.

Resection of Temporal Neocortex During Multiple Hippocampal Transections for Mesial Temporal Lobe Epilepsy Does not Affect Seizure or Memory Outcome

BACKGROUND

Multiple hippocampal transection (MHT) is a surgical treatment for mesial temporal lobe epilepsy associated with improved postoperative neuropsychological outcomes compared with lobectomy.

OBJECTIVE

To determine whether resection of the amygdala and anterior temporal neocortex during MHT affects postoperative seizure/memory outcome.

METHODS

Seventeen patients with normal magnetic resonance imaging and stereo-electroencephalogram-proven drug-resistant dominant mesial temporal lobe epilepsy were treated with MHT. Nine patients underwent MHT alone (MHT–) and 8 patients underwent MHT plus removal of the amygdala and anterior 4.5 cm of temporal neocortex lateral to the fusiform gyrus (MHT+). Verbal and visual-spatial memory were assessed in all patients preoperatively and in 14 patients postoperatively using the Wechsler Memory Scale. Postoperative seizure control was assessed at 12 months for all patients.

RESULTS

Overall, 11 of 17 patients (64.7%) were Engel class 1 at 1 year (6/9 MHT–, 5/8 MHT+, P = .38), and 10 of 14 patients (71.4%) had no significant postoperative decline in either verbal or visual memory (6/8 MHT–, 4/6 MHT+, P = .42). Verbal memory declined in 2 of 8 MHT– and 1 of 6 MHT+ patients, and visual memory declined in 1 of 8 MHT– and 2 of 6 MHT+ patients. Two patients had improved visual memory postoperatively, both in the MHT+ group.

CONCLUSION

MHT on the dominant side is associated with high rates of seizure freedom and favorable memory preservation outcomes regardless of the extent of neocortical resection. Preservation of the temporal neocortex and amygdala during MHT does not appear to decrease the risk of postoperative memory decline, nor does it alter seizure outcome.

Systematic Review of Cognitive Function in Euthymic Bipolar Disorder and Pre-Surgical Temporal Lobe Epilepsy

BACKGROUND

Bipolar disorder (BD) and temporal lobe epilepsy (TLE) overlap in domains including epidemiology, treatment response, shared neurotransmitter involvement and temporal lobe pathology. Comparison of cognitive function in both disorders may indicate temporal lobe mediated processes relevant to BD. This systematic review examines neuropsychological test profiles in euthymic bipolar disorder type I (BD-I) and pre-surgical TLE and compares experimental designs used.

METHODS

A search of PubMed, PsychINFO, and Scopus using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted. Inclusion criteria were comparison group or pre- to post-surgical patients; reported neuropsychological tests; participants aged 18-60 years. Fifty six studies met criteria: 27 BD-I; 29 TLE.

RESULTS

Deficits in BD-I compared to healthy controls (HC) were in executive function, attention span and verbal memory. Deficits in TLE compared to HC were in executive function and memory. In the pre- to post-surgical comparisons, verbal memory in left temporal lobe (LTL) and, less consistently, visuospatial memory in right temporal lobe (RTL) epilepsy declined following surgery. BD-I studies used comprehensive test batteries in well-defined euthymic patients compared to matched HC groups. TLE studies used convenience samples pre- to post-surgery, comparing LTL and RTL subgroups, few included comparisons to HC (5 studies). TLE studies typically examined a narrow range of known temporal lobe-mediated neuropsychological functions, particularly verbal and visuospatial memory.

CONCLUSION

Both disorders exhibit deficits in executive function and verbal memory suggestive of both frontal and temporal lobe involvement. However, deficits in TLE are measured pre- to post-surgery and not controlled at baseline pre-surgery. Further research involving a head-to-head comparison of the two disorders on a broad range of neuropsychological tests is needed to clarify the nature and extent of cognitive deficits and potential overlaps.

Mapping the convergent temporal epileptic network in left and right temporal lobe epilepsy

Left and right mesial temporal lobe epilepsy (mTLE) with hippocampal sclerosis (HS) exhibits similar functional and clinical dysfunctions, such as depressive mood and emotional dysregulation, implying that the left and right mTLE may share a common network substrate. However, the convergent anatomical network disruption between the left and right HS remains largely uncharacterized. This study aimed to investigate whether the left and right mTLE share a similar anatomical network. We examined 43 (22 left, 21 right) mTLE patients with HS and 39 healthy controls using diffusion tensor imaging. Machine learning approaches were applied to extract the abnormal anatomical connectivity patterns in both the left and right mTLE. The left and right mTLE showed that 28 discriminating connections were exactly the same when compared to the controls. The same 28 connections showed high discriminating power in comparisons of the left mTLE versus controls (91.7%) and the right mTLE versus controls (90.0%); however, these connections failed to discriminate the left from the right mTLE. These discriminating connections, which were diminished both in the left and right mTLE, were primarily located in the limbic-frontal network, partially agreeing with the limbic-frontal dysregulation model of depression. These findings suggest that left and right mTLE share a convergent circuit, which may account for the mood and emotional deficits in mTLE and may suggest the neuropathological mechanisms underlying the comorbidity of depression and mTLE.

A quantitative analysis of (1)H-MR spectroscopy at 3.0 T of three brain regions from childhood to middle age

OBJECTIVE

To study age-related metabolic changes in different brain regions.

METHODS

Point-resolved spectroscopy (repetition time/echo time = 2000 ms/30 ms) was performed in the left and right hippocampus, the left thalamus and the left centrum semiovale of 80 healthy subjects (37 females and 43 males aged 7-64 years). Analysis of covariance and linear regression were used for statistical analysis. Both metabolite concentration ratios with respect to total creatine (tCr) and absolute metabolite concentrations were included for analysis.

RESULTS

Ins (myo-inositol)/tCr (p < 0.001) and absolute Ins concentration (p = 0.031) were significantly increased with age after adolescence. NAA (N-acetylaspartic acid)/tCr (p < 0.001) and absolute NAA concentration (p = 0.010) significantly declined with age after adolescence.

CONCLUSION

Age-related increase of Ins and decline of NAA are found in all three regions, especially at the hippocampus, indicating possible gliosis in the ageing brain.

ADVANCES IN KNOWLEDGE

We could use NAA/tCr and Ins/tCr as an indicator to estimate the neurons-to-glial cells ratio at the thalamus. This may be an index to distinguish normal tissues from gliosis.

Quantitative MRI in refractory temporal lobe epilepsy: relationship with surgical outcomes

Medically intractable temporal lobe epilepsy (TLE) remains a serious health problem. Across treatment centers, up to 40% of patients with TLE will continue to experience persistent postoperative seizures at 2-year follow-up. It is unknown why such a large number of patients continue to experience seizures despite being suitable candidates for resective surgery. Preoperative quantitative MRI techniques may provide useful information on why some patients continue to experience disabling seizures, and may have the potential to develop prognostic markers of surgical outcome. In this article, we provide an overview of how quantitative MRI morphometric and diffusion tensor imaging (DTI) data have improved the understanding of brain structural alterations in patients with refractory TLE. We subsequently review the studies that have applied quantitative structural imaging techniques to identify the neuroanatomical factors that are most strongly related to a poor postoperative prognosis. In summary, quantitative imaging studies strongly suggest that TLE is a disorder affecting a network of neurobiological systems, characterized by multiple and inter-related limbic and extra-limbic network abnormalities. The relationship between brain alterations and postoperative outcome are less consistent, but there is emerging evidence suggesting that seizures are less likely to remit with surgery when presurgical abnormalities are observed in the connectivity supporting brain regions serving as network nodes located outside the resected temporal lobe. Future work, possibly harnessing the potential from multimodal imaging approaches, may further elucidate the etiology of persistent postoperative seizures in patients with refractory TLE. Furthermore, quantitative imaging techniques may be explored to provide individualized measures of postoperative seizure freedom outcome.

Bringing memory fMRI to the clinic: comparison of seven memory fMRI protocols in temporal lobe epilepsy

fMRI is increasingly implemented in the clinic to assess memory function. There are multiple approaches to memory fMRI, but limited data on advantages and reliability of different methods. Here, we compared effect size, activation lateralisation, and between‐sessions reliability of seven memory fMRI protocols: Hometown Walking (block design), Scene encoding (block design and event‐related design), Picture encoding (block and event‐related), and Word encoding (block and event‐related). All protocols were performed on three occasions in 16 patients with temporal lobe epilepsy (TLE). Group T‐maps showed activity bilaterally in medial temporal lobe for all protocols. Using ANOVA, there was an interaction between hemisphere and seizure‐onset lateralisation (P = 0.009) and between hemisphere, protocol and seizure‐onset lateralisation (P = 0.002), showing that the distribution of memory‐related activity between left and right temporal lobes differed between protocols and between patients with left‐onset and right‐onset seizures. Using voxelwise intraclass Correlation Coefficient, between‐sessions reliability was best for Hometown and Scenes (block and event). The between‐sessions spatial overlap of activated voxels was also greatest for Hometown and Scenes. Lateralisation of activity between hemispheres was most reliable for Scenes (block and event) and Words (event). Using receiver operating characteristic analysis to explore the ability of each fMRI protocol to classify patients as left‐onset or right‐onset TLE, only the Words (event) protocol achieved a significantly above‐chance classification of patients at all three sessions. We conclude that Words (event) protocol shows the best combination of between‐sessions reliability of the distribution of activity between hemispheres and reliable ability to distinguish between left‐onset and right‐onset patients. Hum Brain Mapp 36:1595–1608, 2015. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Aetiology of cognitive impairment in children with frontal lobe epilepsy

OBJECTIVES

Cognitive impairment is frequent in children with frontal lobe epilepsy (FLE), but its aetiology is unknown. MRI scans often reveal no structural brain abnormalities that could explain the cognitive impairment. This does not exclude more subtle morphological abnormalities that can only be detected by automated morphometric techniques.

AIMS

With these techniques, we investigate the relationship between cortical brain morphology and cognitive functioning in a cohort of children with FLE and healthy controls.

MATERIALS AND METHODS

Thirty-four children aged 8-13 years with FLE of unknown cause and 41 healthy age-matched controls underwent neuropsychological assessment and structural brain MRI. Patients were grouped as cognitively impaired or unimpaired. Intracranial volume, white matter volume, lobular cortical volume, cortical thickness and volumes of cortex structures were compared between patients and controls, and potential correlations with cognitive status were determined.

RESULTS

The group of cognitively impaired children with FLE had significantly smaller left temporal cortex volumes, specifically middle temporal grey matter volume and entorhinal cortex thickness. In addition, cognitively impaired children with FLE had smaller volumes of structures in the left and right frontal cortex, right temporal cortex and the left subcortical area.

CONCLUSION

Cognitively impaired children with FLE have smaller volumes of various cortex structures within the frontal lobes and in extra-frontal regions, most notably temporal cortex volumes. These findings might well explain the broad scale of cognitive domains affected in children with FLE complicated by cognitive impairment and highlight that FLE impacts on areas beyond the frontal lobe.

Temporal lobe surgery in childhood and neuroanatomical predictors of long-term declarative memory outcome

See Berg (doi:10.1093/brain/awu320) for a scientific commentary on this article.

In a long-term follow-up study of children who underwent temporal lobe surgery for treatment of epilepsy, Skirrow et al. identify no significant pre-to-post-surgery memory losses, but instead robust improvements in memory functions supported by the unoperated temporal lobe. The integrity of remaining temporal lobe structures places constraints on long-term memory outcomes.

The temporal lobes play a prominent role in declarative memory function, including episodic memory (memory for events) and semantic memory (memory for facts and concepts). Surgical resection for medication-resistant and well-localized temporal lobe epilepsy has good prognosis for seizure freedom, but is linked to memory difficulties in adults, especially when the removal is on the left side. Children may benefit most from surgery, because brain plasticity may facilitate post-surgical reorganization, and seizure cessation may promote cognitive development. However, the long-term impact of this intervention in children is not known. We examined memory function in 53 children (25 males, 28 females) who were evaluated for epilepsy surgery: 42 underwent unilateral temporal lobe resections (25 left, 17 right, mean age at surgery 13.8 years), 11 were treated only pharmacologically. Average follow-up was 9 years (range 5–15). Post-surgical change in visual and verbal episodic memory, and semantic memory at follow-up were examined. Pre- and post-surgical T₁-weighted MRI brain scans were analysed to extract hippocampal and resection volumes, and evaluate post-surgical temporal lobe integrity. Language lateralization indices were derived from functional magnetic resonance imaging. There were no significant pre- to postoperative decrements in memory associated with surgery. In contrast, gains in verbal episodic memory were seen after right temporal lobe surgery, and visual episodic memory improved after left temporal lobe surgery, indicating a functional release in the unoperated temporal lobe after seizure reduction or cessation. Pre- to post-surgical change in memory function was not associated with any indices of brain structure derived from MRI. However, better verbal memory at follow-up was linked to greater post-surgical residual hippocampal volumes, most robustly in left surgical participants. Better semantic memory at follow-up was associated with smaller resection volumes and greater temporal pole integrity after left temporal surgery. Results were independent of post-surgical intellectual function and language lateralization. Our findings indicate post-surgical, hemisphere-dependent material-specific improvement in memory functions in the intact temporal lobe. However, outcome was linked to the anatomical integrity of the temporal lobe memory system, indicating that compensatory mechanisms are constrained by the amount of tissue which remains in the operated temporal lobe. Careful tailoring of resections for children undergoing epilepsy surgery may enhance long-term memory outcome.

White matter microstructure complements morphometry for predicting verbal memory in epilepsy

Verbal memory is the most commonly impaired cognitive domain in patients with temporal lobe epilepsy (TLE). Although damage to the hippocampus and adjacent temporal lobe structures is known to contribute to memory impairment, little is known of the relative contributions of white versus gray matter structures, or whether microstructural versus morphometric measures of temporal lobe pathology are stronger predictors of impairment. We evaluate whether measures of temporal lobe pathology derived from diffusion tensor imaging (DTI; microstructural) versus structural MRI (sMRI; morphometric) contribute the most to memory performances in TLE, after controlling for hippocampal volume (HCV). DTI and sMRI were performed on 26 patients with TLE and 35 controls. Verbal memory was measured with the Logical Memory (LM) subtest of the Wechsler Memory Scale-III. Hierarchical regression analyses were performed to examine unique contributions of DTI and sMRI measures to verbal memory with HCV entered in block 1. In patients, impaired recall was associated with increased mean diffusivity (MD) of multiple fiber tracts that project through the temporal lobes. In addition, increased MD of the left cortical and bilateral pericortical white matter was associated with impaired recall. After controlling for left HCV, only microstructural measures of white matter pathology contributed to verbal recall. The best predictive model included left HCV and MD of the left inferior longitudinal fasciculus (ILF) and pericortical white matter beneath the left entorhinal cortex. This model explained 60% of the variance in delayed recall and revealed that MD of the left ILF was the strongest predictor. These data reveal that white matter microstructure within the temporal lobe can be used in conjunction with left HCV to enhance the prediction of verbal memory impairment, and speak to the complementary nature of DTI and sMRI for understanding cognitive dysfunction in epilepsy and possibly other memory disorders.

A case report of a Wada test after dominant hemisphere multiple hippocampal transections: Pathophysiology of confusion after amobarbital injection

Dialepsis is defined as a predominant alteration of consciousness with preservation of motor tone and the ability to perform movements. While dialepsis is a common feature of both focal and generalized epilepsies, its precise symptomatogenic zone and pathogenesis remain undefined. This case report describes a patient who underwent intracarotid amobarbital procedures before and after dominant hemisphere multiple hippocampal transections. From our observations, we propose a possible pathogenesis for the generation of dialeptic seizures.

Transsylvian hippocampal transection for mesial temporal lobe epilepsy: surgical indications, procedure, and postoperative seizure and memory outcomes

Object

Amygdalohippocampectomy is a well-established, standard surgery for medically intractable mesial temporal lobe epilepsy (MTLE). However, in the case of MTLE without hippocampal atrophy or sclerosis, amygdalohippocampectomy is associated with decreased postoperative memory function. Hippocampal transection (HT) has been developed to overcome this problem. In HT the hippocampus is not removed; rather, the longitudinal hippocampal circuits of epileptic activities are disrupted by transection of the pyramidal layer of the hippocampus. The present study describes a less invasive modification of HT (transsylvian HT) and presents the seizure and memory outcomes for this procedure.

Methods

Thirty-seven patients with MTLE (18 men and 19 women; age range 9–63 years; 19 with surgery on the right side and 18 with surgery on the left side; seizure onset from 3 to 34 years) who were treated with transsylvian HT were retrospectively analyzed. All patients had left-side language dominance, and follow-up periods ranged from 12 to 94 months (median 49 months). Seizure outcomes were evaluated for all patients by using the Engel classification. Memory function was evaluated for 22 patients based on 3 indices (verbal memory, nonverbal memory, and delayed recall), with those scores obtained using the Wechsler Memory Scale–Revised. Patients underwent evaluation of the memory function before and after surgery (6 months–1 year).

Results

Engel Class I (completely seizure free) was achieved in 25 patients (67.6%). Class II and Class III designation was achieved in 10 (27%) and 2 patients (5.4%), respectively. There were differences in memory outcome between the sides of operation. On the right side, verbal memory significantly increased postoperatively (p = 0.003) but nonverbal memory and delayed recall showed no significant change after the operation (p = 0.718 and p = 0.210, respectively). On the left side, all 3 indices (verbal memory, nonverbal memory, and delayed recall) showed no significant change (p = 0.331, p = 0.458, and p = 0.366, respectively).

Conclusions

Favorable seizure outcome and preservation of verbal memory were achieved with transsylvian HT for the treatment of MTLE without hippocampal atrophy or sclerosis.

Characterizing functional integrity: intraindividual brain signal variability predicts memory performance in patients with medial temporal lobe epilepsy

Computational modeling suggests that variability in brain signals provides important information regarding the system's capacity to adopt different network configurations that may promote optimal responding to stimuli. Although there is limited empirical work on this construct, a recent study indicates that age-related decreases in variability across the adult lifespan correlate with less efficient and less accurate performance. Here, we extend this construct to the assessment of cerebral integrity by comparing fMRI BOLD variability and fMRI BOLD amplitude in their ability to account for differences in functional capacity in patients with focal unilateral medial temporal dysfunction. We were specifically interested in whether either of these BOLD measures could identify a link between the affected medial temporal region and memory performance (as measured by a clinical test of verbal memory retention). Using partial least-squares analyses, we found that variability in a set of regions including the left hippocampus predicted verbal retention and, furthermore, this relationship was similar across a range of cognitive tasks measured during scanning (i.e., the same pattern was seen in fixation, autobiographical recall, and word generation). In contrast, signal amplitude in the hippocampus did not predict memory performance, even for a task that reliably activates the medial temporal lobes (i.e., autobiographical recall). These findings provide a powerful validation of the concept that variability in brain signals reflects functional integrity. Furthermore, this measure can be characterized as a robust biomarker in this clinical setting because it reveals the same pattern regardless of cognitive challenge or task engagement during scanning.