The relationship between quantitative MRI and neuropsychological functioning in temporal lobe epilepsy

Mechanical pain sensitivity is associated with hippocampal structural integrity

ABSTRACT

Rodents and human studies indicate that the hippocampus, a brain region necessary for memory processing, responds to noxious stimuli. However, the hippocampus has yet to be considered a key brain region directly involved in the human pain experience. One approach to answer this question is to perform quantitative sensory testing on patients with hippocampal damage-ie, medial temporal lobe epilepsy. Some case studies and case series have performed such tests in a handful of patients with various types of epilepsy and have reported mixed results. Here, we aimed to determine whether mechanical pain sensitivity was altered in patients diagnosed with temporal lobe epilepsy. We first investigated whether mechanical pain sensitivity in patients with temporal lobe epilepsy differs from that of healthy individuals. Next, in patients with temporal lobe epilepsy, we evaluated whether the degree of pain sensitivity is associated with the degree of hippocampal integrity. Structural integrity was based on hippocampal volume, and functional integrity was based on verbal and visuospatial memory scores. Our findings show that patients with temporal lobe epilepsy have lower mechanical pain sensitivity than healthy individuals. Only left hippocampal volume was positively associated with mechanical pain sensitivity-the greater the hippocampal damage, the lower the sensitivity to mechanical pain. Hippocampal measures of functional integrity were not significantly associated with mechanical pain sensitivity, suggesting that the mechanisms of hippocampal pain processing may be different than its memory functions. Future studies are necessary to determine the mechanisms of pain processing in the hippocampus.

Detecting accelerated long-term forgetting remotely in a community sample of people with epilepsy: Evidence from the Crimes and Four Doors tests

People with epilepsy often report experiencing memory problems though these are not always detectable using standard neuropsychological measures. One form of difficulty that may be relatively prevalent in epilepsy is termed accelerated long-term forgetting (ALF), typically described as relatively greater loss of memory over days or weeks following initial encoding. The current study used remote assessment to examine memory and forgetting over one week in a broad community sample of people with epilepsy and healthy control participants, using two recently developed tests, one verbal (the Crimes test) and one visual (the Four Doors test). These were administered as part of a short battery of cognitive measures, run remotely with participants over Zoom. Across this community-derived sample, people with epilepsy reported more memory complaints and demonstrated significantly faster forgetting on both the verbal and visual tests. This difference was not attributable to level of initial learning performance and was not detectable through delayed recall on a standard existing test. Our results suggests that ALF may be more common than suspected in people with epilepsy, leading to a potentially important source of memory problems that are currently undetected by standard memory tests.

Cortical microstructural gradients capture memory network reorganization in temporal lobe epilepsy

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

Accelerated long-term forgetting of recall and recognition memory in people with epilepsy

PURPOSE

Persons with epilepsy (PWE) report memory deficits as one of the most distressing aspects of their disorder. Recently, a long-term memory deficit known as Accelerated Long-Term Forgetting (ALF) has been described in PWE. ALF is characterized by the initial retention of learned information, followed by an accelerated rate of memory decay. However, the rate of ALF varies widely across literature and it is unclear how it impacts different memory retrieval types. The current study aimed to capture the time course of ALF on both free recall and recognition memory using a movie-based task in PWE.

METHODS

A sample of 30 PWE and 30 healthy comparison (HC) subjects watched a nature documentary and were tested on their recall and recognition of the film's content immediately after viewing and at delays of 24 hours, 48 hours, and 72 hours. Participants also rated the confidence they had in their recognition memory trial responses.

RESULTS

For recall, PWE exhibit ALF at 72 hours (β = -19.840, SE = 3.743, z(226) = -5.301, p < 0.001). For recognition, PWE had decreased performance compared to controls at the 24-hour (β = -10.165, SE = 4.174, z(224) = -3.166, p = 0.004), 48-hour (β = -8.113, SE = 3.701, z(224) = -2.195, p = 0.044), and 72-hour (β = -10.794, SE = 3.017, z(224) = -3.295, p = 0.003) delays. The PWE group showed positive correlations (tau = 0.165, p < 0.001) between confidence ratings and accuracy, with higher confidence reflecting successful recognition. PWE were 49% less likely to answer either retrieval type correctly at 72 hours (OR 0.51, 95% CI [0.35, 0.74], p < 0.001). Left hemispheric seizure onset decreased the odds of successful retrieval by 88% (OR 0.12, 95% CI [0.01, 0.42], p = 0.019).

CONCLUSIONS

These findings provide evidence of ALF in PWE, with a differential impact on recall and recognition memory. This further supports the call to include ALF assessments in standard memory evaluations in PWE. Additionally, identifying the neural correlates of ALF in the future will be important in developing targeted therapies to alleviate the burden of memory impairment for PWE.

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

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

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

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

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.

Cortical-Subcortical morphometric signature of hot water epilepsy patients

BACKGROUND

Cortical and subcortical grey matter (GM) morphometric changes have been demonstrated Temporal Lobe Epilepsy (TLE) or Idiopathic Generalized Epilepsies (IGE). Hot Water Epilepsy (HWE) has not hitherto been studied in these perspectives.

PURPOSE

To investigate the cortical and subcortical grey matter in subjects with HWE in terms of thickness, volume, and surface area using Surface-Based Morphometry (SBM). To assess relationships of SBM-derived metrics with clinical variables.

MATERIALS AND METHODS

Ninety-nine people with HWE and 50 age-matched healthy controls underwent high resolution volumetric MRI brain. These were processed with FreeSurfer to obtain SBM parameters i:e cortical thickness, cortical volume, and Cortical surface area. Volumes of seven subcortical GM structures (hippocampus, globus pallidus, nucleus ambiguous(NA), caudate nucleus, putamen, thalamus, and amygdala) were computed. Intergroup morphometric differences and their correlation with epilepsy-specific clinical variables were calculated.

RESULTS

SBM revealed a global reduction in bihemispheric cortical thickness and left hemispheric cortical volume. Besides, a regional difference in the morphometric measures was noted in temporo-limbic, parietal, pre-cuneus, and the cingulate region. Reduced volume of thalami and left caudate alongside an increased volume of the bilateral amygdala, bilateral nucleus ambiguous (NA), right caudate, and putamen was the other cardinal observation.

CONCLUSION

HWE subjects show alterations in the morphometry of the cortical ribbon and the subcortical grey matter. The temporal semiology, 'reflex nature' pathophysiology correlates involvement of temporo-limbic structures/somatosensory cortex, while the involvement of structures like pre-cuneus, posterior cingulate, and frontal regions are in agreement with functional networks related loss of awareness. That bilateral amygdala swelling occurs in HWE is a novel observation and may signal that it could be a distinct variant of Mesial TLE.

Mesial temporal lobe epilepsy: Revisiting the relation of hippocampal volumetry with memory deficits

OBJECTIVE

Neuropsychological tests can infer the lateralization of the epileptogenic focus, associating verbal memory to mesial structures in the left temporal lobe and visual or nonverbal memory to the right side. High-field magnetic resonance imaging (MRI) with high-resolution protocols allows acquisitions suitable for advanced postprocessing with precise volumetry of brain structures, and functional MRI demonstrates evidence that epilepsy should be seen as a network pathology, involving several structures in the brain. Since the literature showing associations between the volumetry of brain structures in left and right mesial temporal lobe epilepsy (MTLE) and verbal and visual memory performance on neuropsychological tests is conflicting, we revisited these relationships, considering the hippocampal volumetry of patients with unilateral MTLE.

METHODS

Automatized hippocampal volumes were obtained using FreeSurfer software from MRI exams of 35 patients with unilateral MTLE and hippocampal atrophy and homolateral ictal onset zone defined by video electroencephalography concordant to the side of hippocampal volume reduction (15 on the left side). Verbal memory was assessed using the Rey Auditory-Verbal Learning Test (RAVLT), and visual memory tests employed the Rey-Osterrieth Complex Figure Test (ROCFT). The statistical analysis explored relationships between hippocampal volumetry, lateralization, and performance on memory tests.

RESULTS

In general, we observed deficits in both verbal and visual memory for patients with left and right hippocampal volume reduction. Patients with left hippocampal volume reduction had poorer performance on verbal memory tests compared with those with right hippocampal atrophy (t = -3.813, p < 0.001). Visual memory deficits were seen on both left and right MTLE without a statistically significant difference (t = 0.074, p = 0.942). The correlation between the Hippocampal Asymmetry Index (HAI) and visual and verbal Z-scores was significant only for visual Z-score in right MTLE (R = -0.45, p = 0.048).

CONCLUSIONS

Verbal memory deficit seems to be more consistent in patients with left hippocampal volume reduction. Although it had only a moderate correlation to HAI, visual memory deficit is suggested as a poorer indicator for right MTLE. Considering that verbal and visual memory deficits are seen on both right and left MTLE, MTLE should not be regarded as a unilateral, focal, or local insult but as a multifactorial and network pathology, possibly involving several brain structures.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Neuropsychology of the temporal lobe: Luria's and contemporary conceptions

Brain lesion studies currently employ techniques such as computed tomography, functional magnetic resonance imaging, single photon emission tomography and positron emission tomography. Famous neuropsychologist Alexander Romanovich Luria's studies on cognition were conducted without the use of imaging technology for many years, in a large number of patients with brain lesions, and explored complex behavior and specific brain functions involving the lobes and subareas. For instance, he carried out several specific studies on memory and mental organization, reported in his books. The objective of this study is to associate recent studies in neuropsychology with Luria's work specifically on the temporal lobe. According to the data studied, Luria's epistemological foundation remains the basis for neuropsychological studies today, but new data on the temporal lobe in relation to epilepsy and hippocampus analysis have been introduced into the scope of neuropsychology. This study focuses on earlier data from Luria's studies on the neuropsychological functions of the temporal lobe, comparing these with more recent data. However, in order to improve clinical aspects, a detailed study on the neuropsychological tests used for the temporal lobe should be performed.

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 relationship between structural MRI, FDG-PET, and memory in temporal lobe epilepsy: Preliminary results

Structural and metabolic abnormalities of the temporal lobe are frequently found in temporal lobe epilepsy (TLE). In the present retrospective study, we investigated whether structural abnormalities evident in magnetic resonance imaging (MRI) and hypometabolism evident in [¹⁸F]fluorodeoxyglucose positron emission tomography (FDG-PET) independently influence verbal and nonverbal learning and delayed memory in patients with TLE. Sixty-eight patients with refractory unilateral TLE (35 left TLE, 33 right TLE) were divided into three groups: (1) no evidence of pathology in either MRI or FDG-PET studies (MRI-/PET-, n=15), (2) temporal FDG-PET determined hypometabolism with normal MRI findings (MRI-/PET+, n=21), and (3) evidence of temporal abnormalities in both MRI and FDG-PET studies (MRI+/PET+, n=32). A fourth group (MRI+/PET-, n=4) was too small for further statistical analysis and could not be included. Patients with MRI+/PET+ showed worse verbal memory than patients with MRI-/PET- (p<0.01), regardless of side of seizure focus. Verbal memory performance of patients with MRI-/PET+ was located between patients with MRI+/PET+ and MRI-/PET-, although group differences did not achieve statistical significance (ps>0.1). No group differences were found for nonverbal memory (p=0.27). Our results may suggest an interactive negative effect of metabolic and structural temporal lobe abnormalities on verbal memory. Still, our results are preliminary and need further validation by studies involving larger patient groups and up-to date quantitative imaging analysis methods.

Red flags in epilepsy surgery: Identifying the patients who pay a high cognitive price for an unsuccessful surgical outcome

Preoperative estimates of cognitive and seizure outcome must be as accurate as possible if the candidate is to make an informed decision about epilepsy surgery. Significant declines in memory function are reported in approximately 30% of temporal lobe surgery patients. The percentage varies according to the ways in which a postoperative deterioration is defined but since the majority of outcome studies do not take into account the patient's capacity to deteriorate if they are functioning at or close to the floor of a memory test prior to surgery, the published percentages may be an underrepresentation of the true extent of memory decline following epilepsy surgery. We examined the cognitive 'cost' of epilepsy surgery in a consecutive series of 474 patients who underwent elective surgery for medically intractable epilepsy. All patients underwent a presurgical assessment prior to and 1year after the surgery. Reliable change indices were used to identify significant postoperative memory decline. Postoperative outcome was dichotomized using the ILAE 2008 classification. All patients in class one were classified as seizure-free (67.5% of the sample). Excluding patients already functioning at or below the 2nd percentile on standardized memory tests, 37.8% experienced a significant postoperative decline in memory function. Twelve percent experienced the 'double hit' of significant postoperative memory decline and ongoing seizures following surgery. Patients with pathologies other than hippocampal sclerosis and with signs of limited cognitive reserve, both in terms of memory function and overall intellectual ability were most likely to suffer a double hit. Our results indicate that caution should be exercised when operating on these patients and preoperative counseling should be tailored to reflect the likely risk/benefit ratio of a temporal lobe resection for medically intractable epilepsy in this group.

Impact of hippocampal subfield histopathology in episodic memory impairment in mesial temporal lobe epilepsy and hippocampal sclerosis

OBJECTIVE

The objective of the study was to analyze preoperative visual and verbal episodic memories in a homogeneous series of patients with mesial temporal lobe epilepsy (MTLE) and unilateral hippocampal sclerosis (HS) submitted to corticoamygdalohippocampectomy and its association with neuronal cell density of each hippocampal subfield.

METHODS

The hippocampi of 72 right-handed patients were collected and prepared for histopathological examination. Hippocampal sclerosis patterns were determined, and neuronal cell density was calculated. Preoperatively, two verbal and two visual memory tests (immediate and delayed recalls) were applied, and patients were divided into two groups, left and right MTLE (36/36).

RESULTS

There were no statistical differences between groups regarding demographic and clinical data. Cornu Ammonis 4 (CA4) neuronal density was significantly lower in the right hippocampus compared with the left (p=0.048). The groups with HS presented different memory performance - the right HS were worse in visual memory test [Complex Rey Figure, immediate (p=0.001) and delayed (p=0.009)], but better in one verbal task [RAVLT delayed (p=0.005)]. Multiple regression analysis suggested that the verbal memory performance of the group with left HS was explained by CA1 neuronal density since both tasks were significantly influenced by CA1 [Logical Memory immediate recall (p=0.050) and Logical Memory and RAVLT delayed recalls (p=0.004 and p=0.001, respectively)]. For patients with right HS, both CA1 subfield integrity (p=0.006) and epilepsy duration (p=0.012) explained Complex Rey Figure immediate recall performance. Ultimately, epilepsy duration also explained the performance in the Complex Rey Figure delayed recall (p<0.001).

SIGNIFICANCE

Cornu Ammonis 1 (CA1) hippocampal subfield was related to immediate and delayed recalls of verbal memory tests in left HS, while CA1 and epilepsy duration were associated with visual memory performance in patients with right HS.

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.

Asymmetric behaviours of brain oscillations in the human hippocampus during spatial navigation tasks

Hippocampal-dependent memory functions may be lateralized to the right hippocampus during spatial navigation. However, direct electrophysiological evidence supporting these findings in the bilateral hippocampi during spatial navigation has not been well documented in humans. We studied changes in brain oscillations between the dominant and the nondominant hippocampi during encoding periods of environmental novelty using spatial navigation tasks. Results showed that brain oscillations during the encoding period of spatial navigation increased significantly in the nondominant hippocampus compared with the dominant hippocampus. These findings provide direct electrophysiological evidence that the nondominant hippocampus plays a predominant role in spatial navigation.

Spreading activation in nonverbal memory networks

Theories of spreading activation primarily involve semantic memory networks. However, the existence of separate verbal and visuospatial memory networks suggests that spreading activation may also occur in visuospatial memory networks. The purpose of the present investigation was to explore this possibility. Specifically, this study sought to create and describe the design frequency corpus and to determine whether this measure of visuospatial spreading activation was related to right hemisphere functioning and spreading activation in verbal memory networks. We used word frequencies taken from the Controlled Oral Word Association Test and design frequencies taken from the Ruff Figural Fluency Test as measures of verbal and visuospatial spreading activation, respectively. Average word and design frequencies were then correlated with measures of left and right cerebral functioning. The results indicated that a significant relationship exists between performance on a test of right posterior functioning (Block Design) and design frequency. A significant negative relationship also exists between spreading activation in semantic memory networks and design frequency. Based on our findings, the hypotheses were supported. Further research will need to be conducted to examine whether spreading activation exists in visuospatial memory networks as well as the parameters that might modulate this spreading activation, such as the influence of neurotransmitters.

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

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

The new approach to epilepsy classification: Cognition and behavior in adult epilepsy syndromes

The revised terminology and concepts for the organization of seizures and epilepsy proposed by the ILAE Commission on Classification and Terminology in 2010 allows for a number of new opportunities in the study of cognition and behavior in adults. This review examines the literature that has looked for behavioral and cognitive correlates of the newly recognized genetic epilepsies in adults. While some studies report clear cognitive phenotypes associated with specific genetic mutations in adults with epilepsy, others report remarkable clinical heterogeneity. In the second part of this review, we discuss some of the factors that may influence the findings in this literature. Cognitive function is the product of both genetic and environmental influences. Neuropsychological phenotypes under direct genetic influence may be wider and more subtle than specific deficits within discreet cognitive domains and may be reflected in broader, multidimensional measures of cognitive function than those tapped by scores on standardized tests of function. Future studies must be carefully designed to reflect these factors. It is also imperative that studies with negative findings are assigned as much value as those with positive results and published accordingly. This article is part of a Special Issue titled "The new approach to classification: Rethinking cognition and behavior in epilepsy.

Reprint of: The new approach to epilepsy classification: Cognition and behavior in adult epilepsy syndromes

The revised terminology and concepts for the organization of seizures and epilepsy proposed by the ILAE Commission on Classification and Terminology in 2010 allows for a number of new opportunities in the study of cognition and behavior in adults. This review examines the literature that has looked for behavioral and cognitive correlates of the newly recognized genetic epilepsies in adults. While some studies report clear cognitive phenotypes associated with specific genetic mutations in adults with epilepsy, others report remarkable clinical heterogeneity. In the second part of this review, we discuss some of the factors that may influence the findings in this literature. Cognitive function is the product of both genetic and environmental influences. Neuropsychological phenotypes under direct genetic influence may be wider and more subtle than specific deficits within discreet cognitive domains and may be reflected in broader, multidimensional measures of cognitive function than those tapped by scores on standardized tests of function. Future studies must be carefully designed to reflect these factors. It is also imperative that studies with negative findings are assigned as much value as those with positive results and published accordingly. This article is part of a Special Issue titled "The new approach to classification: Rethinking cognition and behavior in epilepsy".

Temporal lobe volume predicts Wada memory test performance in patients with mesial temporal sclerosis

The Wada test is widely used in the presurgical evaluation of potential temporal lobectomy patients to predict postoperative memory function. Expected asymmetry (EA), defined as Wada memory lateralized to the nonsurgical hemisphere, or a higher score after injection of the surgical hemisphere would be considered favorable in terms of postoperative memory outcome. However, in some cases, nonlateralized memory (NM) results, with no appreciable asymmetry, may occur because of impaired scores after both injections, often leading to denial of surgery. The reason for such nonlateralized Wada memory in patients with intractable temporal lobe epilepsy (TLE) remains unclear. Given that quantitative morphometric magnetic resonance imaging studies in TLE patients have shown bilateral regional atrophy in temporal and extratemporal structures, we hypothesized that the volume loss in contralateral temporal structures could contribute to nonlateralized Wada memory performance. To investigate this, we examined the relationship between the volume changes of temporal structures and Wada memory scores in patients with intractable TLE with mesial temporal sclerosis (MTS) using an age- and gender-matched control group. Memory was considered nonlateralized if the absolute difference in the total correct recall scores between ipsilateral and contralateral injections was <11%. Among 21 patients, Wada memory was lateralized in 15 and nonlateralized in 6 patients, with all the nonlateralized scores being observed in left TLE. The recall scores after ipsilateral injection were significantly lower in patients with an NM profile than an EA profile (23 ± 14% vs. 59 ± 18% correct recall, p ≤ 0.001). However, the recall scores after contralateral injection were low but similar between the two groups (25 ± 17% vs. 25 ± 15% correct recall, p=0.97). Compared to controls, all the patients showed greater volume loss in the temporal regions. However, patients with a NM profile showed significantly more volume loss than those with a lateralized memory profile in both contralateral and ipsilateral temporal regions (p<0.05). Left hemispheric Wada memory performance correlated positively with the size of the left mesial and neocortical temporal structures (r=0.49-0.63, p=0.005-0.04). Our study suggests that volume loss in the nonsurgical temporal structures is associated with nonlateralized Wada memory results in patients with intractable TLE.

Object and spatial memory after neonatal perirhinal lesions in monkeys

The contribution of the perirhinal cortex (PRh) to recognition memory is well characterized in adults, yet the same lesions have limited effect on recognition of spatial locations. Here, we assessed whether the same outcomes will follow when perirhinal lesions are performed in infancy. Monkeys with neonatal perirhinal (Neo-PRh) lesions and control animals were tested in three operant recognition tasks as they reached adulthood: Delayed Nonmatching-to-Sample (DNMS) and Object Memory Span (OMS), measuring object recognition, and Spatial Memory Span (SMS), measuring recognition of spatial locations. Although Neo-PRh lesions did not impact acquisition of the DNMS rule, they did impair performance when the delays were extended from 30s to 600s. In contrast, the same neonatal lesions had no impact on either the object or spatial memory span tasks, suggesting that the lesions impacted the maintenance of information across longer delays and not memory capacity. Finally, the magnitude of recognition memory impairment after the Neo-PRh lesions was similar to that previously observed after adult-onset perirhinal lesions, indicating minimal, or no, functional compensation after the early PRh lesions. Overall, the results indicate that the PRh is a cortical structure that is important for the normal development of mechanisms supporting object recognition memory. Its contribution may be relevant to the memory impairment observed with human cases of temporal lobe epilepsy without hippocampal sclerosis, but not to the memory impairment found in developmental amnesia cases.

Gray and White Matter Volumes and Cognitive Dysfunction in Drug-Naïve Newly Diagnosed Pediatric Epilepsy

Epilepsy patients often have cognitive dysfunction even at early stages of disease. We investigated the relationship between structural findings and neuropsychological status in drug-naïve newly diagnosed pediatric epilepsy patients. Thirty newly diagnosed pediatric epilepsy patients and 25 healthy control subjects aged 7~16 years were enrolled, who were assessed by the Korean version of the Wechsler Intelligence Scale for Children (K-WISC-III), the Stroop test, and the trail making test (TMT). Optimized voxel-based morphometry (VBM) was performed for both Gray Matter (GM) and White Matter (WM) volumes. Lower performance levels of verbal intelligence quotient, freedom from distractibility, and executive function were observed in epilepsy group. Interestingly, poor performance in these cognitive subdomains was correlated with regional VBM findings involving both GM and WM volumes, but with different patterns between groups. GM volumes revealed clear differences predominantly in the bilateral frontal regions. These findings indicate that certain cognitive functions may be affected in the early stage of epilepsy, not related to the long-standing epilepsy or medication, but more related to the neurocognitive developmental process in this age. Epilepsy can lead to neuroanatomical alterations in both GM and WM, which may affect cognitive functions, during early stages even before commencement of AED medication.

Regional hippocampal involvement and cognitive impairment in pediatric multiple sclerosis

Objectives:

We assessed global and regional hippocampal volume abnormalities in pediatric multiple sclerosis (MS) patients and their correlations with clinical, neuropsychological and magnetic resonance imaging metrics.

Methods:

From 53 pediatric MS patients and 18 healthy controls, global hippocampal volume was computed using a manual tracing procedure. Regional hippocampal volume modifications were assessed using a radial mapping analysis. MS patients with abnormal performance in three or more tests of a neuropsychological battery for children were classified as cognitively impaired.

Results:

Global hippocampal volume was reduced in MS patients compared with controls, but did not correlate with clinical, neuropsychological and magnetic resonance imaging measures. Compared to controls, MS patients experienced bilateral radial atrophy of the cornu ammonis, subiculum and dentate gyrus subfields as well as radial hypertrophy of the dentate gyrus subfield. Regional hippocampal volume modifications correlated with brain T2 lesion volume as well as attention and language abilities. Global hippocampal volume did not differ between cognitively impaired ( n=12) and cognitively preserved MS patients. Compared to cognitively preserved, cognitively impaired MS patients had atrophy of the subiculum and dentate gyrus subfields of the right hippocampus.

Conclusions:

Hippocampal subregions have different vulnerability to damage in pediatric MS. Regional rather than global hippocampal involvement contributes to global cognitive impairment as well as to deficits of selected cognitive tests.

The role of obesity in cognitive dysfunction in people with epilepsy

OBJECTIVE

In the general population, obesity is associated with accelerated age-related cognitive decline. The impact of obesity on cognitive function in neurological populations who already have a heightened risk of cognitive decline is unknown. This study explored the relationship between obesity and cognitive underfunction in people with medically intractable epilepsy.

METHODS

Eighty-one consecutive patients admitted for evaluation for medically intractable epilepsy (36 females and 45 males) underwent tests of memory and intellectual function. Optimal level of function was assessed using the National Adult Reading Test - Revised. Measures of underfunction were calculated by subtracting current measures of intellectual ability from the NART IQ. Body mass index (BMI) was used as an index of obesity.

RESULTS

Twenty-nine people had a BMI in the healthy range (36%), 31 were overweight (38%), and 21 were obese (26%). The healthy weight, overweight, and obese groups did not differ in age at the time of assessment, age at seizure onset, or optimal level of function (NART IQ). The obese group had a greater degree of suboptimal processing speed and demonstrated a greater degree of underfunction on the Full Scale IQ (FSIQ) measure compared to the healthy weight group. Body mass index accounted for 14% of the variance in underfunction in processing speed and 10% of the variance in underfunction in FSIQ. Controlling for the effects of age, all measures of memory function were significantly correlated with BMI, with poorer scores associated with higher BMIs.

SIGNIFICANCE

A small but significant proportion of the variance in memory function and intellectual underfunction in people with epilepsy is explained by BMI. Further work is needed to establish whether a reduction in BMI to within healthy limits is associated with improvements in cognitive function in this group.

Old dogs with new tricks: Detecting accelerated long-term forgetting by extending traditional measures

Accelerated long-term forgetting (ALF) is a condition in which normal memory performance is displayed after short delays, but significant memory loss is detected when memory is tested after several days or weeks. This condition has been reported in patients with epilepsy, but there are few normative scores available for its detection in clinical practice. In the present study, we assessed 60 healthy control subjects 18-60years of age on three memory measures [Rey Auditory Verbal Learning (RAVLT), Logical Memory (LM), and Aggie Figures] at delays of 30min and 7days. With these normative values, we determined cutoff scores to look for ALF and then categorized the performance of 15 patients with focal epilepsy on the same tasks. Seven of the patients showed ALF, and, in four of these, no other memory deficits (i.e., deficits at 30min on at least one task) were detected. Of the several demographic and epilepsy factors examined, only higher estimated IQ and older age predicted ALF (and only on one task: RAVLT). The findings provide a useful set of data to be applied in the clinic and some insight into the factors that influence retention within the first week.

The relationship between neuropsychological functioning and FDG-PET hypometabolism in intractable mesial temporal lobe epilepsy

We examined the relationship between baseline neuropsychological functioning and 18-fluorodeoxyglucose positron emission tomography (FDG-PET) in intractable mesial temporal lobe epilepsy (MTLE). We hypothesized relationships between dominant temporal lobe hypometabolism and verbal memory and between nondominant temporal lobe hypometabolism and nonverbal memory in line with the lateralized material-specific model of memory deficits in MTLE. We also hypothesized an association between performance on frontal lobe neuropsychological tests and prefrontal hypometabolism. Thirty-two patients who had undergone temporal lobectomy for treatment of MTLE and who completed both presurgical FDG-PET and comprehensive neuropsychological investigations with widely used standardized measures were included. Age-adjusted composite measures were calculated for verbal memory, nonverbal memory, relative material-specific memory, IQ, executive function, attention/working memory, and psychomotor speed. Fluorodeoxyglucose positron emission tomography was analyzed with statistical parametric mapping (SPM) to identify hypometabolism relative to healthy controls. Pearson's correlation was used to determine the relationship between regions of hypometabolism and neuropsychological functioning. Dominant temporal lobe hypometabolism was associated with relatively inferior verbal memory, while nondominant temporal lobe hypometabolism was associated with inferior nonverbal memory. No relationship was found between performance on any frontal lobe measures and prefrontal hypometabolism. Statistical parametric mapping-quantified lateralized temporal lobe hypometabolism correlates with material-specific episodic memory impairment in MTLE. In contrast, prefrontal hypometabolism is not associated with performance on frontal lobe measures. We suggest that this is because frontal lobe neuropsychology tests may not be good measures of isolated frontal lobe functioning.

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.

Displaced aggression predicts switching deficits in people with temporal lobe epilepsy

This study examined the relationship between task-switching abilities and displaced aggression in people with temporal lobe epilepsy (PWE). Participants (35 PWE and 35 healthy controls) performed emotion and gender classification switching tasks. People with temporal lobe epilepsy showed larger switch costs than controls. This result reflected task-switching deficits in PWE. People with temporal lobe epilepsy reported higher anger rumination, revenge planning, and behavioral displaced aggression compared with controls. Displaced aggression was a significant predictor of the task switch costs. It is suggested that displaced aggression is a significant marker of task-switching deficits.

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.

Real-life memory and spatial navigation in patients with focal epilepsy: ecological validity of a virtual reality supermarket task

Ecological assessment and training of real-life cognitive functions such as visual-spatial abilities in patients with epilepsy remain challenging. Some studies have applied virtual reality (VR) paradigms, but external validity of VR programs has not sufficiently been proven. Patients with focal epilepsy (EG, n=14) accomplished an 8-day program in a VR supermarket, which consisted of learning and buying items on a shopping list. Performance of the EG was compared with that of healthy controls (HCG, n=19). A comprehensive neuropsychological examination was administered. Real-life performance was investigated in a real supermarket. Learning in the VR supermarket was significantly impaired in the EG on different VR measures. Delayed free recall of products did not differ between the EG and the HCG. Virtual reality scores were correlated with neuropsychological measures of visual-spatial cognition, subjective estimates of memory, and performance in the real supermarket. The data indicate that our VR approach allows for the assessment of real-life visual-spatial memory and cognition in patients with focal epilepsy. The multimodal, active, and complex VR paradigm may particularly enhance visual-spatial cognitive resources.

Neural correlates of de novo depression following left temporal lobe epilepsy surgery: a voxel based morphometry study of pre-surgical structural MRI

PURPOSE

To investigate cerebral grey matter (GM) volumetric abnormalities in temporal lobe epilepsy (TLE) patients who develop de novo depression following TLE surgery using voxel-based morphometry (VBM).

METHODS

We retrospectively examined pre-surgical grey matter (GM) volumes in 30 patients with TLE due to unilateral left-sided hippocampal sclerosis using 1.5-T MRI scan, which were segmented with optimised VBM parameters and normalised to a sample template using DARTEL, with SPM8 software. Voxel-wise GM differences between patients that developed de novo post-surgical depression (n=5) were compared with patients with no pre- or postoperative psychiatric diagnoses (n=25), using independent samples t-tests with age, gender and secondary generalised tonic-clonic seizures (SGTCS) as covariates (p<.001, unc).

KEY FINDINGS

Reduced preoperative bilateral GM in orbitofrontal cortices (OFC) and ipsilateral cingulate gyrus and thalamus were significantly associated with the development of de novo depression within 4 years postoperatively. Further analyses revealed no differences in seizure freedom (ILAE 1 vs 2-6) or postoperative memory decline between the groups.

SIGNIFICANCE

Although the development of postoperative de novo depression following TLE surgery is likely to be multi-factorial, our results suggest that bilateral OFC and ipsilateral cingulate gyrus and thalamic atrophy in left-sided TLE patients may play a modulatory role. Abnormalities in these areas have also been implicated in primary mood disorders. Prospective neuroimaging studies with larger cohorts are warranted to replicate these results, and further elucidate the neural correlates of de novo depression.

Low prevalence but high specificity of material-specific memory impairment in epilepsy associated with hippocampal sclerosis

PURPOSE

Material-specific memory impairment is used as a lateralizing tool in the evaluation of temporal lobe epilepsy. Lateralizing ability of material-specific memory deficits in temporal lobe epilepsy remains controversial.

METHODS

We studied memory impairment profiles of verbal and nonverbal memory deficits with eight memory subtests of four neuropsychological instruments (two verbal and two nonverbal) in 87 right-handed patients with epilepsy associated with unilateral mesial temporal sclerosis (MTS; 44 right - R, 43 left - L) and 42 controls, with an IQ >70, at least 8 years of education, and without comorbidities.

KEY FINDINGS

Selective verbal memory impairment was noted in 11 of 43 or 25.6% of left MTS cases, with 82.2% specificity, whereas selective nonverbal memory impairment was noted in 11 of 42 or 26.2% of right MTS cases, with 92% specificity. Nonlateralizing profiles of memory performance were seen in the remaining 65 of 87 patients. Approximately half (46/87 or 52.9%) of the patients had intact memory function in both modalities, equally distributed between patients with right MTS (23/44) and left MTS (23/43). Global impairment of both memory types was seen in 12 of 87 or 13.8% of patients, equally distributed between the two groups (7/43 left and 5/44 right).

SIGNIFICANCE

Lateralizing profiles of selective verbal and nonverbal memory deficits are highly specific for left and right MTS, although infrequently encountered in our patients. Nonlateralizing profiles predominated in this population. These findings suggest hemispheric asymmetry memory function, with complex functional interaction of the hippocampi, and possible compensatory mechanisms in the setting of a unilateral lesion.

Cerebellar volume is linked to cognitive function in temporal lobe epilepsy: a quantitative MRI study

INTRODUCTION

Chronic intractable temporal lobe epilepsy (TLE) is associated with certain comorbidities including cognitive impairment. A less common condition among patients with TLE is intermittent explosive disorder (IED), a specific form of aggressive behavior that has been linked to low intelligence and structural pathology in the amygdala. We aimed to identify other neuroanatomical substrates of both cognitive dysfunction and IED in patients with TLE, with special focus on the cerebellum, a brain region known to participate in functional networks involved in neuropsychological and affective processes.

METHODS

Magnetic resonance imaging-based volumetric data from 60 patients with temporal lobe epilepsy (36 with and 24 without IED) were evaluated. Cerebellar, hippocampal, and total brain volumes were processed separately. In a total of 50 patients, the relationship between volumetric measurements and clinical and neuropsychological data (full-scale, verbal, and performance intelligence quotients) was analyzed.

RESULTS

Intermittent explosive disorder in patients with TLE was not significantly linked to any of the regional volumes analyzed. However, cognitive performance showed a significant association both with total brain volume and cerebellar volume measurements, whereby the left cerebellar volume showed the strongest association. A deviation from normal cerebellar volumes was related to lower intelligence. Of note, left cerebellar volume was influenced by age and duration of epilepsy. Hippocampal volumes had a minor influence on cognitive parameters.

CONCLUSION

Our findings suggest that cerebellar volume is not linked to IED in patients with TLE but is significantly associated with cognitive dysfunction. Our findings support recent hypotheses proposing that the cerebellum has a relevant functional topography.

Neuropsychological outcomes in epilepsy surgery patients with unilateral hippocampal sclerosis and good preoperative memory function

We examined postoperative changes in the memory function of 68 people with unilateral hippocampal sclerosis (HS) who underwent epilepsy surgery and had no previous clinical memory impairments. One in four with right HS (RHS) and one in five with left HS (LHS) in our sample of 323 people with unilateral HS performed within normal limits on memory tests that are sensitive to hippocampal pathology in group studies. People with intact memory function prior to surgery were significantly younger and had higher IQs than those with memory impairments. The majority of those with intact memory functions prior to surgery had significant postoperative declines on the memory measures at the 1-year follow-up and no longer functioned within the average range. People with RHS and left LHS were equally at risk of a postoperative decline. Postoperative deterioration was not related to seizure outcome. A higher IQ appears to protect against postoperative memory decline in this group. This finding does not support the notion that intact memory function in people with unilateral HS represents a migration of memory function to the contralateral structures, and thus protection from surgical insult. People with good preoperative memory function in the context of unilateral HS should therefore be counseled regarding the likelihood of a significant postoperative decline in memory function following a temporal lobe resection.

Practical medical applications of quantitative MR relaxometry

Conventional MR images are qualitative, and their signal intensity is dependent on several complementary contrast mechanisms that are manipulated by the MR hardware and software. In the absence of a quantitative metric for absolute interpretation of pixel signal intensities, one that is independent of scanner hardware and sequences, it is difficult to perform comparisons of MR images across subjects or longitudinally in the same subject. Quantitative relaxometry isolates the contributions of individual MR contrast mechanisms (T1, T2, T2) and provides maps, which are independent of the MR protocol and have a physical interpretation often expressed in absolute units. In addition to providing an unbiased metric for comparing MR scans, quantitative relaxometry uses the relationship between MR maps and physiology to provide a noninvasive surrogate for biopsy and histology. This study provides an overview of some promising clinical applications of quantitative relaxometry, followed by a description of the methods and challenges of acquiring accurate and precise quantitative MR maps. It concludes with three case studies of quantitative relaxometry applied to studying multiple sclerosis, liver iron, and acute myocardial infarction.

Resting state functional connectivity of the hippocampus associated with neurocognitive function in left temporal lobe epilepsy

The majority of patients with temporal lobe epilepsy (TLE) experience disturbances of episodic memory from structural damage or dysfunction of the hippocampus. The objective of this study was to use functional Magnetic Resonance Imaging (fMRI) to identify regions where resting state connectivity to the left hippocampus (LH) is correlated with neuropsychological measures of verbal memory retention in TLE patients. Eleven left TLE (LTLE) patients and 15 control subjects participated in resting state fMRI scans. All LTLE patients underwent neuropsychological testing. Resting state functional connectivity maps to the LH were calculated for each patient, and subsequently used in a multiple regression analysis with verbal memory retention scores as a covariate. The analysis identified brain regions whose connectivity to the LH was linearly related to memory retention scores across the group of patients. In LTLE patients, right sided (contralateral) clusters in the precuneus and inferior parietal lobule (IPL) exhibited increased connectivity to the LH with increased memory retention score; left sided (ipsilateral) regions in the precuneus and IPL showed increased connectivity to the LH with decreased retention score. Patients with high memory retention scores had greater connectivity between the LH-right parietal clusters than between the LH-left parietal clusters; in contrast, control subjects had significantly and consistently greater LH-left hemisphere than LH-right hemisphere connectivity. Our results suggest that increased connectivity in contralateral hippocampal functional pathways within the episodic verbal memory network represents a strengthening of alternative pathways in LTLE patients with strong verbal memory retention abilities.

fMRI of verbal and nonverbal memory processes in healthy and epileptogenic medial temporal lobes

Material-specific memory impairments are a well-established consequence of unilateral medial temporal lobe damage. We used fMRI to investigate encoding and recognition of verbal and nonverbal stimuli using adaptations of tasks used successfully in clinical evaluations of patients with temporal lobe epilepsy (TLE). We studied two patient groups, one with left TLE and one with right TLE, and one group of healthy subjects. Results from the healthy subjects indicated that initial and delayed recognition trials of the verbal task activated the left medial temporal lobe, and the same tasks of the nonverbal task activated the right, confirming the sensitivity to laterality of our clinical tasks. Patients tended to use the opposite hippocampus, but often the parahippocampal gyrus on the same side, compared to the healthy subjects. Since our patients and the healthy groups performed similarly on the memory tasks, we conclude that the patients' activation patterns represent an effective adaptation to the presence of an unhealthy hippocampus.

Microstructural and functional MRI studies of cognitive impairment in epilepsy

Cognitive impairment is the most common comorbidity in children with epilepsy, but its pathophysiology and predisposing conditions remain unknown. Clinical epilepsy characteristics are not conclusive in determining cognitive outcome. Because many children with epilepsy do not have macrostructural magnetic resonance imaging (MRI) abnormalities, the underlying substrate for cognitive impairment may be found at the microstructural or functional level. In the last two decades, new MRI techniques have been developed that have the potential to visualize microstructural or functional abnormalities associated with cognitive impairment. These include volumetric MRI, voxel-based morphometry (VBM), diffusion tensor imaging (DTI), MR spectroscopy (MRS), and functional MRI (fMRI). All of these techniques have shed new light on various aspects associated with, or underlying, cognitive impairment, although their use in epilepsy has been limited and focused mostly on adults. Therefore, in this review, the use of all these different MRI techniques to unravel cognitive impairment in epilepsy is discussed both in adults and children with epilepsy. Volumetric MRI and VBM have revealed significant volume losses in the area of the seizure focus as well as in distant areas. DTI adds evidence of loss of integrity of connections from the seizure focus to distant areas as well as between distant areas. MRS and fMRI have shown impaired function both in the area of the seizure focus as well as in distant structures. For this review we have compiled and compared findings from the various techniques to conclude that cognitive impairment in epilepsy results from a network disorder in which the (micro)structures as well as the functionality can be disturbed.

Accelerated long-term forgetting (ALF) and transient epileptic amnesia (TEA): two cases of epilepsy-related memory disorder

Temporal lobe epilepsy (TLE) has long been associated with memory impairment. Recently, two specific forms of memory complaint in this population have been identified: accelerated long-term forgetting (ALF) and transient epileptic amnesia (TEA). This paper presents neuropsychological data (standard neuropsychological tests and experimental measures) on two patients who presented in the epilepsy clinic with seemingly similar subjective reports of profound memory difficulties. This paper illustrates the differences between TEA and ALF. Our focus was on measuring long-term forgetting utilizing a novel visual and verbal test protocol, with responses elicited via verbal prompts over the telephone at intervals up to 30 days. Whereas patient SK had neuropsychological test evidence of problems with learning plus ALF at short and long intervals without clinical evidence of TEA, patient EB had clinically convincing TEA without neuropsychological test evidence of ALF. In particular, SK showed accelerated forgetting while EB did not. This detailed case work develops our understanding of ALF measurement and demonstrates that ALF and TEA can be dissociated.