Investigation of executive function change following anterior temporal lobectomy: selective normalization of verbal fluency

Long-term effect associated with seizures and dynamic effect associated with treatment on cognitive dysfunction of adult patients with focal epilepsy as evaluated by the Trail Making Test

OBJECTIVE

This study was performed to clarify the utility of the Trail Making Test (TMT) in evaluating the effects of the course of epilepsy on cognitive function by evaluating the course of epileptic seizures and the results of the TMT over time.

METHODS

We performed the TMT twice at a 1-year interval for each patient with focal epilepsy. We performed multiple regression analyses with the first TMT scores as dependent variables and clinical features as independent variables. Next, we performed a multivariate analysis of covariance (MANCOVA) to evaluate the difference between the first and second TMT scores for patients in each seizure prognosis group.

RESULTS

We enrolled 132 adult patients in this study. Multiple regression analyses showed that longer active seizure periods were associated with worse first TMT-B performance (β = .318, p < .001) and B-A (β = .377, p < .001) and that the number of antiseizure medicines was associated with worse first TMT-A performance (β = .186, p = .025). In addition, topiramate and zonisamide adversely affected TMT performance. MANCOVA showed an interaction between the prognosis of TMT-B performance and the seizure prognosis [F(2, 120) = 3.68, p = .028]. Subeffect tests revealed that the second TMT-B performance improved only in the seizure improvement group [F(1, 10) = 10.07, p = .01].

SIGNIFICANCE

Epileptic seizures were shown to be associated with both long-term and dynamic adverse effects on cognitive function evaluated with the TMT in adult patients with focal epilepsy. Seizure control is important for improving the cognitive function of patients with epilepsy; however, the potential adverse effects of polypharmacy and some antiseizure medicines such as zonisamide and topiramate on cognitive function should be considered.

Memory and executive functioning outcomes of selective amygdalohippocampectomy in patients with hippocampal sclerosis: A preliminary study in a developing country

Background

Selective amygdalohippocampectomy (SA) is an effective treatment for drug-resistant cases of epilepsy due to hippocampal sclerosis (HS). However, its neurocognitive outcomes are inconsistent across the previous studies, pointing to potential location-specific confounders. Here, we investigated the neurocognitive outcomes of SA in an Iranian center recently adopting this approach.

Methods

Thirty adults (53.3% of females, age 31.4 ± 6.2 years) with drug-resistant epilepsy due to HS were included in the study. Patients were stratified into surgical (n = 15) and medical (n = 15) treatment groups based on their preferences. Neurocognitive function was assessed before and 6 months after intervention using Wisconsin Card Sorting Test (WCST), Wechsler Adult Intelligence Scale-Revised, and Wechsler Memory Scale- Third Edition (WMS-III). Postintervention performance changes were compared between the two groups, and predictors of worse postoperative outcomes were investigated.

Results

Longitudinal changes of performance in WMS-III and WCST were significantly different between the surgically and medically treated patients. Postoperative WMS-III performance showed an average 25% decline (mean ∆T2-T1 = -25.1%, T = -6.6, P < 0.001), and WCST performance improved by an average of 49% (mean ∆T2-T1 = +49.1%, T = 4.6, P < 0.001). The decline in memory performance was more severe in the left-sided surgery and in patients with higher baseline education (mean ∆T2-T1 = -31.1%, T = -8.9, P < 0.001).

Conclusion

In our center, executive functioning improved or remained stable after SA, but memory functions declined moderately. The left-sided SA and higher education were associated with more severe decline in memory functions, highlighting the need for special considerations for these groups.

Knowledge of language function and underlying neural networks gained from focal seizures and epilepsy surgery

The effects of epilepsy and its treatments have contributed significantly to language models. The setting of epilepsy surgery, which allows for careful pre- and postsurgical evaluation of patients with cognitive testing and neuroimaging, has produced a wealth of language findings. Moreover, a new wave of surgical interventions, including stereotactic laser ablation and radio frequency ablation, have contributed new insights and corrections to language models as they can make extremely precise, focal lesions. This review covers the common language deficits observed in focal dyscognitive seizure syndromes. It also addresses the effects of surgical interventions on language, and highlights insights gained from unique epilepsy assessment methods (e.g., cortical stimulation mapping, Wada evaluation). Emergent findings are covered including a lack of involvement of the hippocampus in confrontation word retrieval, possible roles for key white matter tracts in language, and the often-overlooked basal temporal language area. The relationship between language and semantic memory networks is also explored, with brief consideration given to the prevailing models of semantic processing, including the amodal Hub and distributed, multi-modal processing models.

The impact of epilepsy surgery on the structural connectome and its relation to outcome

Background

Temporal lobe surgical resection brings seizure remission in up to 80% of patients, with long-term complete seizure freedom in 41%. However, it is unclear how surgery impacts on the structural white matter network, and how the network changes relate to seizure outcome.

Methods

We used white matter fibre tractography on preoperative diffusion MRI to generate a structural white matter network, and postoperative T1-weighted MRI to retrospectively infer the impact of surgical resection on this network. We then applied graph theory and machine learning to investigate the properties of change between the preoperative and predicted postoperative networks.

Results

Temporal lobe surgery had a modest impact on global network efficiency, despite the disruption caused. This was due to alternative shortest paths in the network leading to widespread increases in betweenness centrality post-surgery. Measurements of network change could retrospectively predict seizure outcomes with 79% accuracy and 65% specificity, which is twice as high as the empirical distribution. Fifteen connections which changed due to surgery were identified as useful for prediction of outcome, eight of which connected to the ipsilateral temporal pole.

Conclusion

Our results suggest that the use of network change metrics may have clinical value for predicting seizure outcome. This approach could be used to prospectively predict outcomes given a suggested resection mask using preoperative data only.

Functional MRI, resting state fMRI, and DTI for predicting verbal fluency outcome following resective surgery for temporal lobe epilepsy

OBJECTIVE

Predicting cognitive function following resective surgery remains an important clinical goal. Each MRI neuroimaging technique can potentially provide unique and distinct insight into changes that occur in the structural or functional organization of "at-risk" cognitive functions. The authors tested for the singular and combined power of 3 imaging techniques (functional MRI [fMRI], resting state fMRI, diffusion tensor imaging) to predict cognitive outcome following left (dominant) anterior temporal lobectomy for intractable epilepsy. METHODS; The authors calculated the degree of deviation from normal, determined the rate of change in this measure across the pre- and postsurgical imaging sessions, and then compared these measures for their ability to predict verbal fluency changes following surgery.

RESULTS

The data show that the 3 neuroimaging techniques, in a combined model, can reliably predict cognitive outcome following anterior temporal lobectomy for medically intractable temporal lobe epilepsy.

CONCLUSIONS

These findings suggest that these 3 imaging modalities can be used effectively, in an additive fashion, to predict functional reorganization and cognitive outcome following anterior temporal lobectomy.

What does diffusion tensor imaging (DTI) tell us about cognitive networks in temporal lobe epilepsy?

Diffusion tensor imaging (DTI) has provided considerable insight into our understanding of epilepsy as a network disorder, revealing subtle alterations in white matter microstructure both proximal and distal to the epileptic focus. These white matter changes have been shown to assist with lateralizing the seizure focus, as well as delineating the location/anatomy of key white matter tracts (i.e., optic radiations) for surgical planning. However, only recently have studies emerged describing the utility of DTI for probing cognitive networks in patients with epilepsy and for examining the structural plasticity within these networks both before and after epilepsy surgery. Here, we review the current literature describing the use of DTI for understanding language and memory networks in patients with temporal lobe epilepsy (TLE), as well as the extant literature on networks associated with executive functioning and global intelligence. Studies of memory and language reveal a complex network of frontotemporal fibers that contribute to naming and fluency performance in TLE, and demonstrate that these networks appear to undergo adaptive changes in response to surgical intervention. Although studies of executive functioning and global intelligence have been less conclusive, there is accumulating evidence that aberrant communication between frontoparietal and medial temporal networks may underlie working memory impairment in TLE. More recently, multimodal imaging studies have provided evidence that disruptions within these white matter networks co-localize with functional changes observed on functional MRI. However, structure-function associations are not entirely coherent and may breakdown in patients with TLE, especially those with a left-sided seizure focus. Although the reasons for discordant findings are unclear, small sample sizes, heterogeneity within patient populations and limitations of the current tensor model may account for contradictory and null findings. Improvements in imaging hardware and higher field strengths have now paved the way for the implementation of advanced diffusion techniques, and these advanced models show great promise for improving our understanding of how network dysfunction contributes to cognitive morbidity in TLE.

Lexical retrieval pre- and posttemporal lobe epilepsy surgery in a pediatric sample

PURPOSE

This study aimed to evaluate lexical retrieval, presurgery and postsurgery, among children and adolescents who had undergone temporal lobe resection for intractable epilepsy and to compare outcomes in patients whose surgery involved the left temporal lobe or the right temporal lobe.

MATERIALS AND METHODS

A retrospective chart review identified 36 patients from a major pediatric epilepsy treatment center who had undergone temporal lobe resection (21 underwent left temporal lobe resection; 15 underwent right temporal lobe resection) for intractable epilepsy and who had completed neuropsychological testing that included a measure of confrontation naming (Boston Naming Test, BNT) and verbal fluency (Delis-Kaplan Executive Function System (D-KEFS) Fluency) prior to and after surgery. Linear mixed effects regression models were used to evaluate presurgery and postsurgery changes and to compare the left temporal lobe resection group with the right temporal lobe resection group.

PRINCIPAL RESULTS

Confrontation naming performance declined after left, but not right, temporal lobe resection (p<0.05). This effect was not documented for verbal fluency.

MAJOR CONCLUSIONS

Left temporal lobe resection for intractable epilepsy is associated with a decline in lexical retrieval. The risk of decline in specific language functions following surgery involving the left temporal lobe should be incorporated in the counseling of patients and families in decision-making with regard to surgery.

Reading difficulty is associated with failure to lateralize temporooccipital function

OBJECTIVE

Studies of focal epilepsy have revealed abnormalities of language organization; however, little attention has been paid to disorders of reading in this group. We hypothesized that language functional magnetic resonance imaging (fMRI) would reveal differences in language organization between focal epilepsy patients with and without reading difficulties.

METHODS

We conducted language fMRI studies of 10 focal epilepsy patients with reading difficulties, 34 focal epilepsy patients without reading difficulties, and 42 healthy controls.

RESULTS

We defined regions of interests on the basis of activation patterns on an orthographic lexical retrieval task. Comparison of activations within these ROIs on a second Noun-Verb task revealed epilepsy-related effects (relative to healthy controls: reduced activation in left inferior frontal cortex), as well as greater activation in the right temporooccipital cortex specific to the reading difficulty group.

SIGNIFICANCE

These findings identify a focal epilepsy effect in the left frontal region (present in patients with and without reading difficulties), and a functional abnormality specific to the reading difficulty group localized to right temporooccipital cortex-a region implicated in lexicosemantic processing. Our observations suggest a failure of left hemisphere specialization among focal epilepsy patients with reading difficulties.

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.

Assessing the driving performance of a person with epilepsy presurgery and postsurgery

Occupational therapists and certified driving rehabilitation specialists are uniquely skilled to assess functional abilities underlying driving performance. However, little information exists on the utility of clinical assessments to determine driving performance in people with epilepsy. This case study demonstrates how an occupational therapy evaluation battery was used to examine differences in visual and cognitive abilities and simulated driving performance before and after epilepsy surgery. Specifically, a 43-yr-old White man with right anterior lobe epilepsy underwent temporal lobectomy and had his driving-related abilities and simulated driving performance assessed pre- and postsurgery. The occupational therapy evaluation indicated improvements in executive skills, attention, and information processing speed postsurgery. Visuospatial abilities worsened after surgery, likely contributing to the modest increase in vehicle position errors on the driving simulator. Nevertheless, simulated driving performance improved after temporal lobectomy. Reductions in the number of visual scanning, lane maintenance, and speed regulation errors were recorded.

Predictors of decline in verbal fluency after frontal lobe epilepsy surgery

Few studies have focused on language changes following frontal lobe epilepsy (FLE) surgery. The aim of the current study is to quantify the role of resection location and size in verbal fluency decline after FLE surgery and to examine its predictors. A retrospective chart review identified 36 adult patients who underwent FLE surgery. Verbal fluency was assessed using the Controlled Oral Word Association Test (COWAT). Nine (25%) of the patients had significant decline. Binary logistic regression incorporating side of resection and preoperative COWAT score significantly predicted decline and accounted for 25% of the variance. A trend was also noted for decliners to have higher postoperative seizure recurrence (p=0.067). There was no effect of size of resection. Patients undergoing FLE surgery are at risk of verbal fluency decline, especially if they have a high presurgical verbal fluency score, undergo a frontal lobe resection in the language dominant hemisphere, and have poor seizure outcome.

Cognition and resective surgery for diffuse infiltrative glioma: an overview

Compared to classical oncological outcome measures such as time to progression and survival, the importance of cognitive functioning in patients with diffuse infiltrative brain tumors has only recently been recognized. Apart from the relatively low incidence and the invariably fatal outcome of gliomas, the general assumption that cognitive assessment is time-consuming and burdensome contributes to this notion. Our understanding of the effects of brain surgery on cognition, for instance, is largely based on studies in surgical patients with refractory epilepsy, with only a limited number of studies in surgical patients with gliomas. The impact of other factors affecting cognition in glioma patients such as direct tumor effects, radiotherapy and chemotherapy, and medical treatment, including anti-epileptic drugs and steroids, have been studied more extensively. The purpose of this paper is to provide an overview of cognition in patients with diffuse infiltrative gliomas and the impact of resective surgery as well as other tumor and treatment-related factors.

Role of frontotemporal fiber tract integrity in task-switching performance of healthy controls and patients with temporal lobe epilepsy

The objective of this study is to investigate the relationships among frontotemporal fiber tract compromise and task-switching performance in healthy controls and patients with temporal lobe epilepsy (TLE). We performed diffusion tensor imaging (DTI) on 30 controls and 32 patients with TLE (15 left TLE). Fractional anisotropy (FA) was calculated for four fiber tracts [uncinate fasciculus (UncF), arcuate fasciculus (ArcF), dorsal cingulum (CING), and inferior fronto-occipital fasciculus (IFOF)]. Participants completed the Trail Making Test-B (TMT-B) and Verbal Fluency Category Switching (VFCS) test. Multivariate analyses of variances (MANOVAs) were performed to investigate group differences in fiber FA and set-shifting performances. Canonical correlations were used to examine the overall patterns of structural-cognitive relationships and were followed by within-group bivariate correlations. We found a significant canonical correlation between fiber FA and task-switching performance. In controls, TMT-B correlated with left IFOF, whereas VFCS correlated with FA of left ArcF and left UncF. These correlations were not significant in patients with TLE. We report significant correlations between frontotemporal fiber tract integrity and set-shifting performance in healthy controls that appear to be absent or attenuated in patients with TLE. These findings suggest a breakdown of typical structure-function relationships in TLE that may reflect aberrant developmental or degenerative processes.

Frontal lobe function in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is typically associated with long-term memory dysfunction. The frontal lobes support high-level cognition comprising executive skills and working memory that is vital for daily life functioning. Deficits in these functions have been increasingly reported in TLE. Evidence from both the neuropsychological and neuroimaging literature suggests both executive function and working memory are compromised in the presence of TLE. In relation to executive impairment, particular focus has been paid to set shifting as measured by the Wisconsin Card Sorting Task. Other discrete executive functions such as decision-making and theory of mind also appear vulnerable but have received little attention. With regard to working memory, the medial temporal lobe structures appear have a more critical role, but with emerging evidence of hippocampal dependent and independent processes. The relative role of underlying pathology and seizure spread is likely to have considerable bearing upon the cognitive phenotype and trajectory in TLE. The identification of the nature of frontal lobe dysfunction in TLE thus has important clinical implications for prognosis and surgical management. Longitudinal neuropsychological and neuroimaging studies assessing frontal lobe function in TLE patients pre- and postoperatively will improve our understanding further.

Neuropsychological outcomes after epilepsy surgery: Systematic review and pooled estimates

PURPOSE

Epilepsy surgery is a safe surgical procedure, but it may be associated with cognitive changes. Estimates of the risk of decline in specific neuropsychological domains after epilepsy surgery would assist surgical decision making in clinical practice. The goal of this study was to conduct a systematic review to derive pooled estimates of the rate of losses and gains in neuropsychological functions after epilepsy surgery, using empirically based methods for quantifying cognitive change.

METHODS

An extensive literature search using PubMed, EmBase, and the Cochrane database was conducted, yielding 5,061 articles on epilepsy surgery, with 193 on neuropsychological outcomes (IQ, memory, language, executive functioning, attention, and subjective cognitive changes).

KEY FINDINGS

Of these, 23 met final eligibility criteria, with 22 studies involving temporal surgery only. Key aspects of inclusion criteria were N ≥ 20 and use of reliable change index or standardized regression-based change estimates. In addition to the proportion of patients experiencing losses and gains in each individual test, a single pooled estimate of gains and losses for each cognitive domain was derived using a random effects model. Weighted estimates indicated a risk to verbal memory with left-sided temporal surgery of 44%, twice as high as the rate for right-sided surgery (20%). Naming was reduced in 34% of left-sided temporal patients, with almost no patients with gains (4%). Pooled data on IQ, executive functioning, and attention indicated few patients show declines post surgery, but a substantial rate of improvement in verbal fluency with left-sided temporal surgery (27%) was found. Self-reported cognitive declines after epilepsy surgery were uncommon, and gains were reported in some domains where losses were found on objective tests (i.e., verbal memory and language). Variations in surgical techniques did not appear to have a large effect on cognitive outcomes, except for naming outcomes, which appeared better with more conservative resections. Sensitivity to postoperative changes differed across visual memory tests, but not verbal memory tests. Few conclusions could be made regarding cognitive risks and benefits of extratemporal epilepsy surgery, or of epilepsy surgery in children.

SIGNIFICANCE

In sum, epilepsy surgery is associated with specific cognitive changes, but may also improve cognition in some patients. The results provide base rate estimates of expected cognitive gains and losses associated with epilepsy surgery that may prove useful in clinical settings.

Presurgical epilepsy localization with interictal cerebral dysfunction

Localization of interictal cerebral dysfunction with 2-[(18)F]fluoro-2-D-deoxyglucose (FDG) positron emission tomography (PET) and neuropsychological examination usefully supplements electroencephalography (EEG) and brain magnetic resonance imaging (MRI) in planning epilepsy surgery. In MRI-negative mesial temporal lobe epilepsy, correlation of temporal lobe hypometabolism with extracranial ictal EEG can support resection without prior intracranial EEG monitoring. In refractory localization-related epilepsies, hypometabolic sites may supplement other data in hypothesizing likely ictal onset zones in order to intracranial electrodes for ictal recording. Prognostication of postoperative seizure freedom with FDG PET appears to have greater positive than negative predictive value. Neuropsychological evaluation is critical to evaluating the potential benefit of epilepsy surgery. Cortical deficits measured with neuropsychometry are limited in lateralizing and localizing value for determination of ictal onset sites, however. Left temporal resection risks iatrogenic verbal memory deficits and dysnomia, and neuropsychological findings are useful in predicting those at greatest risk. Prognostication of cognitive risks with resection at other sites is less satisfactory.

Extrahippocampal integrity in temporal lobe epilepsy and cognition: thalamus and executive functioning

Chronic temporal lobe epilepsy (TLE) is characterized by the presence of extra-hippocampal brain abnormality and cognitive impairment in both memory and nonmemory domains. However, the link between structural integrity and cognition has not frequently been studied. Forty-six patients with TLE and 61 age-matched controls were studied to determine the predictive relationship between baseline thalamic volume and performance on measures of executive functioning evaluated 4 years later. As expected, the TLE group had lower baseline thalamic volumes than controls and also performed more poorly on measures of executive functioning. Total thalamic volume significantly predicted subsequent performance on all three measures of executive functioning. These findings were maintained when both hippocampal volume and frontal lobe volume were taken into account. These findings add to a growing literature demonstrating a link between extra-hippocampal volume abnormalities and cognitive functioning in TLE.

Presurgical neuropsychological testing predicts cognitive and seizure outcomes after anterior temporal lobectomy

We sought to determine significant predictors of seizure and cognitive outcome following surgery for epilepsy. Participants included 41 patients who had undergone anterior temporal lobectomy (ATL). Higher presurgical verbal/language scores and lower nonverbal memory scores were predictive of seizure-free status following ATL. Overall, the presurgical predictors were 93% accurate in discriminating between seizure-free and non-seizure-free patients postsurgery. Surgery in the nondominant-for-language hemisphere was predictive of higher postsurgical verbal/language and verbal memory scores. Higher presurgical visual/construction, nonverbal memory, and verbal/language scores were predictive of better postsurgical verbal/language functioning. Better presurgical verbal/language functioning was predictive of the same skills postsurgically as well as visual/construction outcomes. Exploratory analyses in a subset of participants (n=25) revealed that dominant and nondominant intracarotid amobarbital (Wada) memory scores added unique variance only for predicting nonverbal memory following ATL. Presurgical neuropsychological testing provides significant and unique information regarding postsurgical seizure freedom and cognitive outcome in patients who have undergone ATL.

Changes in neuropsychological functioning following temporal lobectomy in patients with temporal lobe epilepsy

PURPOSE

This study was conducted to evaluate the changes in neuropsychological functioning in patients with temporal lobe epilepsy (TLE) after temporal lobe resection.

METHODS

Fifty-four TLE patients were evaluated before and after surgery using comprehensive neuropsychological tests to assess general intelligence, executive functioning, language, verbal and visual memory, working memory, visuo-spatial ability, attention and motor function.

RESULTS

The patients with left TLE showed no impairment of neuropsychological functioning after surgery, with the exception of auditory immediate memory. Furthermore, they showed significant improvement in performance IQ, executive function, working memory, visual memory, attention and psychomotor speed. The patients with right TLE did not show any significant impairment in post-operative neuropsychological functioning. They showed improvements in intellectual and executive functions, language, visual memory, visuo-spatial ability, attention and motor function post-operatively. The patients with hippocampal sclerosis showed greater post-operative improvements than the patients without hippocampal sclerosis regardless of the side. Patients with better pre-operative neuropsychological function had a higher chance of successfully discontinuing all seizure medications after surgery.

DISCUSSION

The results of this study suggest that temporal lobectomy does not harm the neuropsychological functioning of patients with intractable TLE and that it improves cognitive functions of the contralateral hemisphere.

Executive deficits in generalized and extrafrontal partial epilepsy: long versus short seizure-free periods

OBJECTIVE

The goal of this study was to examine the influence of seizure freedom on executive function in outpatients with generalized epilepsy and extrafrontal partial epilepsy. Recent investigations of cognitive function in epilepsy have revealed executive deficits in persons with focal temporal as well as generalized epilepsies. Additional studies have suggested an influence of seizure freedom on cognitive function.

METHODS

Thirty-five consecutive outpatients were divided into seizure free <or= 3 months (n=18) and seizure free >3 months (n=17). The neuropsychological tests administered included: verbal fluency tasks, the Cognitive Estimation Test, the Hayling and Brixton Test, and the Behavioural Assessment of the Dysexecutive Syndrome (BADS) battery. Both patient groups were compared with matched healthy controls (n=16).

RESULTS

The extensive testing revealed significant differences between patients with shorter seizure-free periods and healthy controls with respect to overall errors and phonemic verbal fluency, response suppression, and BADS overall profile scores. Subjects seizure free >3 months exhibited a trend toward impairment in the phonemic fluency task only.

CONCLUSIONS

The results suggest that deficits in executive function were present in patients with extrafrontal partial epilepsy and generalized epilepsy, indicating the potential influence of epileptic activity on the ability to focus on relevant information and switch attention to other relevant information, to plan tasks and subtasks, and to check on and encode working memory content. The results also suggest that those deficits may be more pronounced in patients with relatively short seizure-free periods.

Thalamic atrophy and cognition in unilateral temporal lobe epilepsy

This study examined quantitative magnetic resonance volumes of the thalamus and hippocampus and determined their relationship with cognitive function and clinical seizure characteristics in a sample of 46 unilateral temporal lobe epilepsy (TLE) subjects (20 left and 26 right) and 29 controls. The hippocampus and thalamus exhibited different patterns of volume abnormality, different associations with clinical seizure characteristics, and different patterns of relationship with cognitive measures. Hippocampal volume reduction was primarily ipsilateral to the seizure focus, and thalamic volume reduction was bilateral. Ipsilateral hippocampal volume was significantly correlated with both early neurodevelopmental features (age of seizure onset) and disease characteristics (duration of epilepsy), whereas thalamus integrity was related only to disease variables. Hippocampal volume showed a selective association with verbal memory performance. In contrast, both left and right thalamic volumes were significantly correlated with performance on both memory and nonmemory cognitive domains. These findings underscore the importance of thalamic atrophy in chronic TLE and its potential implications for cognition.

Whole-brain voxel-based morphometry of white matter in medial temporal lobe epilepsy

PURPOSE

The purpose of this study was to analyze whole-brain white matter changes in medial temporal lobe epilepsy (MTLE).

MATERIALS AND METHODS

We studied 23 patients with MTLE and 13 age- and sex-matched healthy control subjects using voxel-based morphometry (VBM) on T1-weighted 3D datasets. The seizure focus was right sided in 11 patients and left sided in 12. The data were collected on a 1.5 T MR system and analyzed by SPM 99 to generate white matter density maps.

RESULTS

Voxel-based morphometry revealed diffusively reduced white matter in MTLE prominently including bilateral frontal lobes, bilateral temporal lobes and corpus callosum. White matter reduction was also found in the bilateral cerebellar hemispheres in the left MTLE group.

CONCLUSION

VBM is a simple and automated approach that is able to identify diffuse whole-brain white matter reduction in MTLE.

Pre- and post-operative Wisconsin card sorting test performance in patients with temporal lobe epilepsy due to hippocampal sclerosis

Patients with temporal lobe epilepsy due to hippocampal sclerosis (TLE/HS) have a distinct neuropsychological profile, but there is still debate on whether executive dysfunction is part of this profile and also whether temporal lobe surgery can modify this dysfunction.

A prospective study of the effects of anterior temporal lobectomy on emotion recognition and theory of mind

Nineteen patients evaluated facial emotional expressions and performed 'theory of mind' reasoning tasks before and after a temporal lobectomy for medically intractable epilepsy, and results were compared with the performance of 19 healthy controls. Following operation, which in all cases resulted in excision of the entire amygdala, there was no change in the ability to reason about the mental states of others, in line with the suggestion that the anterior temporal lobe is not necessary for theory of mind reasoning. However, following a left anterior temporal lobectomy, patients evaluated fearful facial expressions in a more normative manner. This may reflect the excision of a 'hyper-excitable' amygdala which pre-operatively misinterprets fearful expressions as containing blends of other emotions. Alternatively the results may represent an improvement in function of the right amygdala following the excision of a noxious inhibitory epileptogenic focus on the left. The finding complements earlier demonstrations that damage to the right amygdala is associated with impaired processing of fear; amelioration of right amygdala function may conversely be associated with an improvement.

Memory and frontal lobe functions; possible relations with dopamine D2 receptors in the hippocampus

Cerebral cortical regions are thought to be important for cognitive functions such as memory and executive function. Although the functional associations between dopamine D2 receptors and motor and cognitive functions have been extensively examined in the striatum using positron emission tomography (PET), the role of dopamine D2 receptors in extrastriatal regions has been unexplored. We aimed to investigate the relationship between dopamine D2 receptors in extrastriatal regions and the performance of a broad spectrum of cognitive functions including memory, language, attention, and executive function in healthy subjects. Extrastriatal dopamine D2 receptors were measured in 25 male subjects using PET with [(11)C]FLB457. After the PET scans, a battery of neuropsychological tests was administered to all subjects. We found that the binding potential (BP) of [(11)C]FLB457 in the hippocampus was positively correlated with memory function. Furthermore, BP of [(11)C]FLB457 in the hippocampus, but not in the prefrontal cortex, was associated with frontal lobe functions such as executive function and verbal fluency. Our findings suggest that dopamine D2 receptors in the hippocampus might affect the local hippocampal function, but also brain functions outside the hippocampus such as the prefrontal cortex.

Executive performance on the Wisconsin Card Sorting Test in mesial temporal lobe epilepsy

Executive dysfunction assessed by the Wisconsin Card Sorting Test has been observed in patients with mesial temporal lobe epilepsy (TLE); however, the mechanism of executive impairment is unclear. We therefore investigated the potential contribution of the hippocampus toward executive dysfunction in 85 mesial TLE patients, and in a control group of 34 patients with neocortical TLE. Standardized regression-based methodology was used for correcting test-retest bias. We found that 56% of mesial TLE patients had impaired sorting performance, with 30% showing severe impairment. A lower full-scale intelligence quotient, older age, longer duration, and preoperative use of topiramate were significantly correlated with poorer preoperative sorting abilities. However, neither these variables nor postoperative discontinuation/reduction of topiramate were related to postoperative changes in sorting abilities. Only preoperative sorting abilities were negatively correlated with postoperative changes in executive performance. That is, patients with better preoperative executive ability showed greater postoperative deterioration in executive function, whereas those with poorer preoperative sorting ability had greater improvement in executive function after mesial temporal resection. There were no differences in card sorting ability between the mesial and neocortical TLE groups. In conclusion, our results suggest that impairment of card sorting performance in the mesial TLE group cannot be explained only by hippocampal dysfunction, but that other processes (possibly epileptic discharges propagated to the extratemporal area) must play a predominant role.

Memory for the past after temporal lobectomy: impact of epilepsy and cognitive variables

A few previous studies have revealed impairments in remote memory in patients with temporal lobe epilepsy, but many questions about the importance of lesion side, type of material, seizure history and deficits in other aspects of cognitive functions remain unanswered. In this study, patients who had undergone unilateral (15 right and 15 left) temporal lobectomy (TL) for the relief of epilepsy and 15 control subjects completed a range of public and autobiographical memory tests. Deficits in recall and recognition of details related to past famous world events were observed for both left and right TL groups. In addition, the left TL group showed impaired retrieval of famous names and TL patients as a group generated significantly fewer names of people from their own past. Current seizure- and medication-status influenced performance on a few measures, but duration of epilepsy and age of onset had no significant impact. Underlying cognitive deficits (especially naming ability) contributed to, but could not completely explain difficulties remembering the past. In particular, deficits in the ability to retrieve highly specific information learned in the past, such as names of famous people or details about famous events, remained evident in analyses that controlled for the impact of related cognitive skills.