Medial temporal fMRI activation reflects memory lateralization and memory performance in patients with epilepsy

The role of multifocal visual evoked potential in detection of minimal hepatic encephalopathy in patients with compensated liver cirrhosis

BACKGROUND

Minimal hepatic encephalopathy (MHE) is one of the most debilitating complications of hepatic cirrhosis, and visual electrophysiology, visual evoked potential (VEP) has long been used for MHE diagnosis. This technique only produces a summed response that is greatly dominated by the macular region. Multifocal visual evoked potential (mfVEP) imaging minimizes these limitations because it allows topographic recording of the optic nerve and visual cortex. The aim of this study was to detect minimal hepatic encephalopathy among cirrhotic patients using the mfVEP in comparison to the validated psychometric hepatic encephalopathy score (PHES), paired associative learning (PAL) and the Benton visual retention test (BVRT).

METHODS

Forty-five patients with compensated hepatic cirrhosis were enrolled in our study and compared to 45 normal controls who were matched for age, sex and educational level. Both groups underwent psychological tests (PHES, PAL, BVRT) and neurophysiological tests (mfVEP).

RESULTS

1According to the validated PHES, 14 patients were found to have MHE, 15 patients were found to have abnormal mfVEP, and abnormalities in the BVRT and PAL were found in 11 and 10 patients, respectively. 2-mfVEP showed the highest sensitivity in the detection of MHE in reference to the PHES. 3- The mfVEP test and potentially the BVRT have the advantage of detecting subtle abnormalities in non-MHE cirrhotic patients, for further research and follow-up are needed.

CONCLUSION

mfVEP demonstates promising results for objective early detection of MHE, with a sensitivity of approximately 92.9%.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Lateralization of the hippocampus: A review of molecular, functional, and physiological properties in health and disease

The hippocampus is a part of the brain's medial temporal lobe that is located under the cortex. It belongs to the limbic system and helps to collect and transfer information from short-term to long-term memory, as well as spatial orientation in each mammalian brain hemisphere. After more than two centuries of research in brain asymmetry, the hippocampus has attracted much attention in the study of brain lateralization. The hippocampus is very important in cognitive disorders, related to seizures and dementia, such as epilepsy and Alzheimer's disease. In addition, the motivation to study the hippocampus has increased significantly due to the asymmetry in the activity of the left and right hippocampi in healthy people, and its disruption during some neurological diseases. After a general review of the hippocampal structure and its importance in related diseases, the asymmetry in the brain with a focus on the hippocampus during the growth and maturation of healthy people, as well as the differences created in patients at the molecular, functional, and physiological levels are discussed. Most previous work indicates that the hippocampus is lateralized in healthy people. Also, lateralization at different levels remarkably changes in patients, and it appears that the most complex cognitive disorder is caused by a new dominant asymmetric system.

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

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

Story reading with incidental comprehension and memory: left hemisphere dominance

BACKGROUND

There are no studies on adults with unilateral brain lesions regarding story reading with incidental/implicit comprehension and memory, in which memory is only assessed through delayed recall. There is a need for validation of cerebral laterality in this type of verbal recall, which includes spontaneous performance (free or uncued condition (UC)), and induced-through-question performance regarding the forgotten units (cued condition (CC)).

OBJECTIVES

To explore the effects of unilateral brain lesions, of oral reading with expression (RE) and comprehension (RC) on delayed recall of a story, as either UC or CC; and to validate the ability of UC and CC to discriminate the side of brain injury.

METHODS

Data were obtained from 200 right-handed volunteers, among whom 42 had left-hemisphere injury (LHI), 49 had right-hemisphere injury (RHI) and 109 were demographically-matched healthy participants (HP). Patients who were unable to read, understand or speak were excluded.

RESULTS

LHI individuals presented impairment of both UC and CC, in relation to the other two groups (non-LHI) with sensitivity and specificity above 70%. LHI and RHI individuals were not significantly different in RE and RC, but they were both different from HP in all the assessments except CC, in which RHI individuals resembled HP. Despite this lack of abnormality in RHI individuals during CC, about half of this group showed impairment in UC. Additionally, whereas RE had a significant effect on UC, the moral of the story (RC) had a significant effect on both UC and CC.

CONCLUSIONS

The left hemisphere was dominant for this memory task involving implicit processing.

In Vivo Imaging of Neuroinflammatory Targets in Treatment-Resistant Epilepsy

PURPOSE OF REVIEW

Recent evidence indicates that chronic, low-level neuroinflammation underlies epileptogenesis. Targeted imaging of key neuroinflammatory cells, receptors, and tissues may enable localizing epileptogenic onset zone, especially in those patients who are treatment-resistant and considered MRI-negative. Finding a specific, sensitive neuroimaging-based biomarker could aid surgical planning and improve overall prognosis in eligible patients. This article reviews recent research on in vivo imaging of neuroinflammatory targets in patients with treatment-resistant, non-lesional epilepsy.

RECENT FINDINGS

A number of advanced approaches based on imaging neuroinflammation are being implemented in order to assist localization of epileptogenic onset zone. The most exciting tools are based on radioligand-based nuclear imaging or revisiting of existing technology in novel ways. The greatest limitations stem from gaps in knowledge about the exact function of neuroinflammatory targets (e.g., neurotoxic or neuroprotective). Further, lingering questions about each approach's specificity, reliability, and sensitivity must be addressed, and clinical utility must be validated before any novel method is incorporated into mainstream clinical practice. Current applications of imaging neuroinflammation in humans are limited and underutilized, but offer hope for finding sensitive and specific neuroimaging-based biomarker(s). Future work necessitates appreciation of investigations to date, significant findings, and neuroinflammatory targets worth exploring further.

Extracellular Vesicles in the Forebrain Display Reduced miR-346 and miR-331-3p in a Rat Model of Chronic Temporal Lobe Epilepsy

An initial precipitating injury in the brain, such as after status epilepticus (SE), evolves into chronic temporal lobe epilepsy (TLE). We investigated changes in the miRNA composition of extracellular vesicles (EVs) in the forebrain after the establishment of SE-induced chronic TLE. We induced SE in young Fischer 344 rats through graded intraperitoneal injections of kainic acid, which resulted in consistent spontaneous recurrent seizures at ~ 3 months post-SE. We isolated EVs from the entire forebrain of chronically epileptic rats and age-matched naïve control animals through an ultracentrifugation method and performed miRNA-sequencing studies to discern changes in the miRNA composition of forebrain-derived EVs in chronic epilepsy. EVs from both naïve and epileptic forebrains displayed spherical or cup-shaped morphology, a comparable size range, and CD63 expression but lacked the expression of a deep cellular marker GM130. However, miRNA-sequencing studies suggested downregulation of 3 miRNAs (miR-187-5p, miR-346, and miR-331-3p) and upregulation of 4 miRNAs (miR-490-5p, miR-376b-3p, miR-493-5p, and miR-124-5p) in EVs from epileptic forebrains with fold changes ranging from 1.5 to 2.4 (p < 0.0006; FDR < 0.05). By using geNorm and Normfinder software, we identified miR-487 and miR-221 as the best combination of reference genes for measurement of altered miRNAs found in the epileptic forebrain through qRT-PCR studies. The validation revealed that only miR-346 and miR-331-3p were significantly downregulated in EVs from the epileptic forebrain. The enrichment pathway analysis of these miRNAs showed an overrepresentation of signaling pathways that are linked to molecular mechanisms underlying chronic epilepsy, including GABA-ergic (miR-346 targets) and mTOR (miR-331-3p targets) systems. Thus, the packaging of two miRNAs into EVs in neural cells is considerably altered in chronic epilepsy. Functional studies on these two miRNAs may uncover their role in the pathophysiology and treatment of TLE.

Chronobiology of limbic seizures: Potential mechanisms and prospects of chronotherapy for mesial temporal lobe epilepsy

Mesial Temporal Lobe Epilepsy (mTLE) characterized by progressive development of complex partial seizures originating from the hippocampus is the most prevalent and refractory type of epilepsy. One of the remarkable features of mTLE is the rhythmic pattern of occurrence of spontaneous seizures, implying a dependence on the endogenous clock system for seizure threshold. Conversely, circadian rhythms are affected by epilepsy too. Comprehending how the circadian system and seizures interact with each other is essential for understanding the pathophysiology of epilepsy as well as for developing innovative therapies that are efficacious for better seizure control. In this review, we confer how the temporal dysregulation of the circadian clock in the hippocampus combined with multiple uncoupled oscillators could lead to periodic seizure occurrences and comorbidities. Unraveling these associations with additional research would help in developing chronotherapy for mTLE, based on the chronobiology of spontaneous seizures. Notably, differential dosing of antiepileptic drugs over the circadian period and/or strategies that resynchronize biological rhythms may substantially improve the management of seizures in mTLE patients.

Memory loss and memory reorganization patterns in temporal lobe epilepsy patients undergoing anterior temporal lobe resection, as demonstrated by pre-versus post-operative functional MRI

This study was aimed to longitudinally assess memory function and whole-brain memory circuit reorganization in patients with temporal lobe epilepsy (TLE) by comparing activation potentials before versus after anterior temporal lobe (ATL) resection. Nineteen patients with medically-intractable TLE (10 left TLE, 9 right TLE) and 15 healthy controls were enrolled. Group analyses were conducted pre- and post-ATL of a novelty complex scene-encoding paradigm comparing areas of blood oxygen-level-dependent (BOLD) signal activations on functional magnetic resonance imaging (fMRI). None of the pre-operative patient characteristics we studied predicted the extent of pre- to post-operative memory loss. On fMRI, extra-temporal activations were detected pre-operatively in both LTLE and RTLE, particularly in the frontal lobe. Greater activations also were noted in the contralateral hippocampus and parahippocampus in both groups. Performing within-subject comparisons, post-op relative to pre-op, pronounced ipsilateral activations were identified in the left parahippocampal gyrus in LTLE, versus the right middle temporal gyrus in RTLE patients. Memory function was impaired pre-operatively but declined after ATL resection in both RTLE and LTLE patients. Post-operative fMRI results indicate possible functional adaptations to ATL loss, primarily occurring within the left parahippocampal gyrus versus right middle temporal gyrus in LTLE versus RTLE patients, respectively.

Task activation and functional connectivity show concordant memory laterality in temporal lobe epilepsy

OBJECTIVE

In epilepsy, asymmetries in the organization of mesial temporal lobe (MTL) functions help determine the cognitive risk associated with procedures such as anterior temporal lobectomy. Past studies have investigated the change/shift in a visual episodic memory laterality index (LI) in mesial temporal lobe structures through functional magnetic resonance imaging (fMRI) task activations. Here, we examine whether underlying task-related functional connectivity (FC) is concordant with such standard fMRI laterality measures.

METHODS

A total of 56 patients with temporal lobe epilepsy (TLE) (Left TLE [LTLE]: 31; Right TLE [RTLE]: 25) and 34 matched healthy controls (HC) underwent fMRI scanning during performance of a scene encoding task (SET). We assessed an activation-based LI of the hippocampal gyrus (HG) and parahippocampal gyrus (PHG) during the SET and its correspondence with task-related FC measures.

RESULTS

Analyses involving the HG and PHG showed that the patients with LTLE had a consistently higher LI (right-lateralized) than that of the HC and group with RTLE, indicating functional reorganization. The patients with RTLE did not display a reliable contralateral shift away from the pathology, with the mesial structures showing quite distinct laterality patterns (HG, no laterality bias; PHG, no evidence of LI shift). The FC data for the group with LTLE provided confirmation of reorganization effects, revealing that a rightward task LI may be based on underlying connections between several left-sided regions (middle/superior occipital and left medial frontal gyri) and the right PHG. The FCs between the right HG and left anterior cingulate/medial frontal gyri were also observed in LTLE. Importantly, the data demonstrate that the areas involved in the LTLE task activation shift to the right hemisphere showed a corresponding increase in task-related FCs between the hemispheres.

SIGNIFICANCE

Altered laterality patterns based on mesial temporal lobe epilepsy (MTLE) pathology manifest as several different phenotypes, varying according to side of seizure onset and the specific mesial structures involved. There is good correspondence between task LI activation and FC patterns in the setting of LTLE, suggesting that reliable visual episodic memory reorganization may require both a shift in nodal activation and a change in nodal connectivity with mesial temporal structures involved in memory.

Temporal and spectral characteristics of dynamic functional connectivity between resting-state networks reveal information beyond static connectivity

Estimation of functional connectivity (FC) has become an increasingly powerful tool for investigating healthy and abnormal brain function. Static connectivity, in particular, has played a large part in guiding conclusions from the majority of resting-state functional MRI studies. However, accumulating evidence points to the presence of temporal fluctuations in FC, leading to increasing interest in estimating FC as a dynamic quantity. One central issue that has arisen in this new view of connectivity is the dramatic increase in complexity caused by dynamic functional connectivity (dFC) estimation. To computationally handle this increased complexity, a limited set of dFC properties, primarily the mean and variance, have generally been considered. Additionally, it remains unclear how to integrate the increased information from dFC into pattern recognition techniques for subject-level prediction. In this study, we propose an approach to address these two issues based on a large number of previously unexplored temporal and spectral features of dynamic functional connectivity. A Generalized Autoregressive Conditional Heteroskedasticity (GARCH) model is used to estimate time-varying patterns of functional connectivity between resting-state networks. Time-frequency analysis is then performed on dFC estimates, and a large number of previously unexplored temporal and spectral features drawn from signal processing literature are extracted for dFC estimates. We apply the investigated features to two neurologic populations of interest, healthy controls and patients with temporal lobe epilepsy, and show that the proposed approach leads to substantial increases in predictive performance compared to both traditional estimates of static connectivity as well as current approaches to dFC. Variable importance is assessed and shows that there are several quantities that can be extracted from dFC signal which are more informative than the traditional mean or variance of dFC. This work illuminates many previously unexplored facets of the dynamic properties of functional connectivity between resting-state networks, and provides a platform for dynamic functional connectivity analysis that facilitates its usage as an investigative measure for healthy as well as abnormal brain function.

Proton magnetic resonance spectroscopy reveals significant decline in the contents of N-acetylaspartylglutamate in the hippocampus of aged healthy subjects

INTRODUCTION

To characterize the contents of choline (Cho), creatine (Cr) and N-acetylaspartylglutamate (NAA) in the hippocampus of healthy volunteers, we investigated the contents and their correlationship with age, gender and laterality.

MATERIAL AND METHODS

Volunteers were grouped into a young, a middle and an old age. The Cho, Cr and NAA contents were determined with proton magnetic resonance spectroscopy (1H-MRS), and the correlationship was analyzed with Pearson correlation.

RESULTS

The concentration of NAA in the bilateral hippocampi was markedly lower in the old than in the young and the middle (LSD test, all p < 0.025). Furthermore, NAA/Cr in the bilateral hippocampi head (left: 1.10 ±0.40 vs. 1.54 ±0.49 or 1.43 ±0.49; right: 1.04 ±0.42 vs. 1.35 ±0.40 or 1.30 ±0.42), region 1 of the bilateral hippocampal body (left: 1.24 ±0.53 vs. 1.58 ±0.58 or 1.35 ±0.44; right: 1.30 ±0.43 vs. 1.54 ±0.51 or 1.35 ±0.51) and region 2 of the left hippocampal body (1.21 ±0.32 vs. 1.46 ±0.36 or 1.36 ±0.44) and the left hippocampal tail (1.11 ±0.40 vs. 1.36 ±0.47 or 1.15 ±0.32) was significantly higher in the old than in the young and the middle, respectively (all p < 0.026). The NAA content in the bilateral hippocampal head, body and tail negatively correlated with age. Moreover, the NAA, Cho and Cr contents in the hippocampal body and the tail were higher in the right than the left.

CONCLUSIONS

The NAA content of the hippocampal head, body and tail were significantly decreased in the old compared with younger persons, and it negatively correlates with age. The NAA, Cho and Cr contents exhibit laterality in the hippocampal body and tail.

Practice guideline summary: Use of fMRI in the presurgical evaluation of patients with epilepsy: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

OBJECTIVE

To assess the diagnostic accuracy and prognostic value of functional MRI (fMRI) in determining lateralization and predicting postsurgical language and memory outcomes.

METHODS

An 11-member panel evaluated and rated available evidence according to the 2004 American Academy of Neurology process. At least 2 panelists reviewed the full text of 172 articles and selected 37 for data extraction. Case reports, reports with <15 cases, meta-analyses, and editorials were excluded.

RESULTS AND RECOMMENDATIONS

The use of fMRI may be considered an option for lateralizing language functions in place of intracarotid amobarbital procedure (IAP) in patients with medial temporal lobe epilepsy (MTLE; Level C), temporal epilepsy in general (Level C), or extratemporal epilepsy (Level C). For patients with temporal neocortical epilepsy or temporal tumors, the evidence is insufficient (Level U). fMRI may be considered to predict postsurgical language deficits after anterior temporal lobe resection (Level C). The use of fMRI may be considered for lateralizing memory functions in place of IAP in patients with MTLE (Level C) but is of unclear utility in other epilepsy types (Level U). fMRI of verbal memory or language encoding should be considered for predicting verbal memory outcome (Level B). fMRI using nonverbal memory encoding may be considered for predicting visuospatial memory outcomes (Level C). Presurgical fMRI could be an adequate alternative to IAP memory testing for predicting verbal memory outcome (Level C). Clinicians should carefully advise patients of the risks and benefits of fMRI vs IAP during discussions concerning choice of specific modality in each case.

Neural Stem Cell or Human Induced Pluripotent Stem Cell-Derived GABA-ergic Progenitor Cell Grafting in an Animal Model of Chronic Temporal Lobe Epilepsy

Grafting of neural stem cells (NSCs) or GABA-ergic progenitor cells (GPCs) into the hippocampus could offer an alternative therapy to hippocampal resection in patients with drug-resistant chronic epilepsy, which afflicts >30% of temporal lobe epilepsy (TLE) cases. Multipotent, self-renewing NSCs could be expanded from multiple regions of the developing and adult brain, human embryonic stem cells (hESCs), and human induced pluripotent stem cells (hiPSCs). On the other hand, GPCs could be generated from the medial and lateral ganglionic eminences of the embryonic brain and from hESCs and hiPSCs. To provide comprehensive methodologies involved in testing the efficacy of transplantation of NSCs and GPCs in a rat model of chronic TLE, NSCs derived from the rat medial ganglionic eminence (MGE) and MGE-like GPCs derived from hiPSCs are taken as examples in this unit. The topics comprise description of the required materials, reagents and equipment, methods for obtaining rat MGE-NSCs and hiPSC-derived MGE-like GPCs in culture, generation of chronically epileptic rats, intrahippocampal grafting procedure, post-grafting evaluation of the effects of grafts on spontaneous recurrent seizures and cognitive and mood impairments, analyses of the yield and the fate of graft-derived cells, and the effects of grafts on the host hippocampus. © 2016 by John Wiley & Sons, Inc.

Frequency Specificity of fMRI in Mesial Temporal Lobe Epilepsy

Medial temporal lobe epilepsy (mTLE) is a system-level disease characterized by aberrant neuronal synchronization and widespread alterations in function. Previous studies have focused on the amplitude analysis of the blood oxygenation level-dependent (BOLD) signals to reveal the aberrant alterations in mTLE. However, these methods did not work well in the cases where the amplitudes of two oscillations are correlated but the underlying oscillations are neither phase coherent nor frequency consistent. To address this problem, we investigated the differences of frequency specificity between patients with mTLE and healthy controls using the extreme-point symmetric mode decomposition (ESMD) method. In this method, the BOLD signals were decomposed into a set of intrinsic mode functions (IMFs) and the instantaneous frequency of each IMF was calculated using the direct interpolation strategy. The intrinsic frequency (denoted as Freq) for every voxel was obtained by the weighted sum of the instantaneous frequencies of all the IMFs. The Freq was used as an index to evaluate the altered frequency specificity of 41 patients with mTLE (17 right-side, 24 left-side) and 24 healthy control subjects. The results show that the peak of frequency distribution curve for the patients moves towards the higher frequency than that for the healthy controls. Compared with the healthy control group, the patients with left mTLE demonstrate higher Freq in the default mode network, middle frontal gyrus, insula, middle temporal gyrus and calcarine gyrus; the patients with right mTLE demonstrate higher Freq in the precuneus and occipital lobe. For the three groups, the distinct frequency distribution appears in the left and right hippocampus due to the hippocampal structural and functional asymmetries. The preliminary results imply that the frequency-specific correlated oscillations in the distributed brain regions can provide information about the nature of diseases affecting the brain and the alterations of frequency specificity are associated with the pathological characteristics of mTLE.

Large-scale brain networks are distinctly affected in right and left mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) with hippocampus sclerosis (HS) is associated with functional and structural alterations extending beyond the temporal regions and abnormal pattern of brain resting state networks (RSNs) connectivity. We hypothesized that the interaction of large-scale RSNs is differently affected in patients with right- and left-MTLE with HS compared to controls. We aimed to determine and characterize these alterations through the analysis of 12 RSNs, functionally parceled in 70 regions of interest (ROIs), from resting-state functional-MRIs of 99 subjects (52 controls, 26 right- and 21 left-MTLE patients with HS). Image preprocessing and statistical analysis were performed using UF(2) C-toolbox, which provided ROI-wise results for intranetwork and internetwork connectivity. Intranetwork abnormalities were observed in the dorsal default mode network (DMN) in both groups of patients and in the posterior salience network in right-MTLE. Both groups showed abnormal correlation between the dorsal-DMN and the posterior salience, as well as between the dorsal-DMN and the executive-control network. Patients with left-MTLE also showed reduced correlation between the dorsal-DMN and visuospatial network and increased correlation between bilateral thalamus and the posterior salience network. The ipsilateral hippocampus stood out as a central area of abnormalities. Alterations on left-MTLE expressed a low cluster coefficient, whereas the altered connections on right-MTLE showed low cluster coefficient in the DMN but high in the posterior salience regions. Both right- and left-MTLE patients with HS have widespread abnormal interactions of large-scale brain networks; however, all parameters evaluated indicate that left-MTLE has a more intricate bihemispheric dysfunction compared to right-MTLE. Hum Brain Mapp 37:3137-3152, 2016. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

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

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

The effect of medial temporal lobe epilepsy on visual memory encoding

Effective visual memory encoding, a function important for everyday functioning, relies on episodic and semantic memory processes. In patients with medial temporal lobe epilepsy (MTLE), memory deficits are common as the structures typically involved in seizure generation are also involved in acquisition, maintenance, and retrieval of episodic memories. In this study, we used group independent component analysis (GICA) combined with Granger causality analysis to investigate the neuronal networks involved in visual memory encoding during a complex fMRI scene-encoding task in patients with left MTLE (LMTLE; N=28) and in patients with right MTLE (RMTLE; N=18). Additionally, we built models of memory encoding in LMTLE and RMTLE and compared them with a model of healthy memory encoding (Nenert et al., 2014). For those with LMTLE, we identified and retained for further analyses and model generation 7 ICA task-related components that were attributed to four different networks: the frontal and posterior components of the DMN, visual network, auditory-insular network, and an "other" network. For those with RMTLE, ICA produced 9 task-related components that were attributed to the somatosensory and cerebellar networks in addition to the same networks as in patients with LMTLE. Granger causality analysis revealed group differences in causality relations within the visual memory network and MTLE-related deviations from normal network function. Our results demonstrate differences in the networks for visual memory encoding between those with LMTLE and those with RMTLE. Consistent with previous studies, the organization of memory encoding is dependent on laterality of seizure focus and may be mediated by functional reorganization in chronic epilepsy. These differences may underlie the observed differences in memory abilities between patients with LMTLE and patients with RMTLE and highlight the modulating effects of epilepsy on the network for memory encoding.

A model for visual memory encoding

Memory encoding engages multiple concurrent and sequential processes. While the individual processes involved in successful encoding have been examined in many studies, a sequence of events and the importance of modules associated with memory encoding has not been established. For this reason, we sought to perform a comprehensive examination of the network for memory encoding using data driven methods and to determine the directionality of the information flow in order to build a viable model of visual memory encoding. Forty healthy controls ages 19-59 performed a visual scene encoding task. FMRI data were preprocessed using SPM8 and then processed using independent component analysis (ICA) with the reliability of the identified components confirmed using ICASSO as implemented in GIFT. The directionality of the information flow was examined using Granger causality analyses (GCA). All participants performed the fMRI task well above the chance level (>90% correct on both active and control conditions) and the post-fMRI testing recall revealed correct memory encoding at 86.33 ± 5.83%. ICA identified involvement of components of five different networks in the process of memory encoding, and the GCA allowed for the directionality of the information flow to be assessed, from visual cortex via ventral stream to the attention network and then to the default mode network (DMN). Two additional networks involved in this process were the cerebellar and the auditory-insular network. This study provides evidence that successful visual memory encoding is dependent on multiple modules that are part of other networks that are only indirectly related to the main process. This model may help to identify the node(s) of the network that are affected by a specific disease processes and explain the presence of memory encoding difficulties in patients in whom focal or global network dysfunction exists.

Contributions of fMRI towards our understanding of the response to psychosocial stress in epilepsy and psychogenic nonepileptic seizures

There are multiple definitions of stress. For this review, as a reference point, we will use the concept of acute emotional/psychosocial stress ("stress"). The presence of acute stress has been reported to have a significant effect on seizure control, with several studies showing patients with seizure disorders being able to predict with reasonable accuracy seizure occurrence within the following hours or days. However, neuroimaging investigations of the pathophysiological mechanisms underlying stress reactivity (e.g., hypothalamic-pituitary-adrenal (HPA) axis activation) in humans, in general, and in patients with seizure disorders, in particular, are scarce. The reasons for this are multiple and likely include difficulty with designing appropriate probes that test various aspects of stress response, obtaining approval for studies that induce stress in patients who are prone to having stress-induced seizures, difficulties with assessing the physiological response to stress inside the scanner (e.g., heart rate, respiratory rate, oxygenation, cortisol levels, and galvanic skin responses), participant identification, and choice of epilepsy syndrome for investigation. With the recent explosion of neuroimaging literature focusing on correlating stress of various types and levels with cortical activations in healthy and diseased populations, it is incumbent upon us to examine the available neuroimaging data in patients with seizure disorders in order to identify the existing gaps and the needs/directions for future investigations. This approach is consistent with the goals of several of the 2014 Benchmarks for Epilepsy Research for the National Institute of Neurological Disorders and Stroke and the American Epilepsy Society.

Functional neuro-imaging as a pre-surgical tool in epilepsy

Functional neuro-imaging techniques are helpful in the pre-surgical evaluation of epilepsy for localization of the epileptogenic zone as ancillary tools to electroencephalography (EEG) and magnetic resonance imaging (MRI) or when other localization techniques are normal, non-concordant or discordant. Positron emission tomography (PET) and ictal single photon emission computed tomography (ictal SPECT) imaging are traditional tests that have been reported to have good sensitivity and specificity although the results are better with more expertise as is true for any technique. More recently magnetoencephalogram/magnetic source imaging (MEG/MSI), diffusion tensor imaging and functional magnetic resonance imaging (fMRI) have been used in localization and functional mapping during the pre-surgical work-up of epilepsy. Newer techniques such as fMRI-EEG, functional connectivity magnetic resonance imaging and near infra-red spectroscopy, magnetic resonance spectroscopy and magneto nanoparticles hold promise for further development that could then be applied in the work-up of epilepsy surgery. In this manuscript, we review these techniques and their current position in the pre-surgical evaluation of epilepsy.

Binge drinking trajectory and neuropsychological functioning among university students: a longitudinal study

BACKGROUND

Adolescence is a time of considerable neurodevelopment. Binge drinking (BD) during this period increases the vulnerability to its neurotoxic effects. This longitudinal study aimed to investigate the relationship between BD trajectory over university years and neuropsychological functioning.

METHODS

Cohort-study. Two-year follow-up. A total of 89 university students were assessed: 40 Non-BD (at Initial and Follow-up), 16 Ex-BD (BD at Initial but not at Follow-up) and 33 BD (at both times). Neuropsychological assessment of working memory, episodic memory and executive abilities was carried out during their first (Initial) and third (Follow-up) academic year at the University of Santiago de Compostela.

RESULTS

BD subjects performed less well on the Wechsler Memory Scale-III (WMS-III) Logical Memory Subtest (immediate theme recall, P=.034; delayed theme recall, P=.037; and percent retention, P=.035) and committed more perseverative errors on the Self-Ordered Pointing Task (SOPT) (P=.021) than Non-BD. There were no differences between Ex-BD and Non-BD.

CONCLUSIONS

Binge drinking trajectory during adolescence is associated with neuropsychological performance. Persistent BD, but not Ex-BD, is associated with verbal memory and monitoring difficulties. This is compatible with the hypothesis that heavy alcohol use during adolescence may affect cognitive functions that rely on the temporomesial and dorsolateral prefrontal cortex.

Immunological functioning in Alzheimer's disease: differential effects of relative left versus right temporoparietal dysfunction

The cerebral hemispheres are differentially involved in regulating immunological functioning and the neuropathology associated with Alzheimer's disease (AD) is asymmetrical. Thus, subgroups of AD patients may exhibit different patterns of immunological dysfunction. We explored this possibility in a group of AD patients and found that patients with low white blood cell counts and low lymphocyte numbers exhibited better performance on tests of right temporoparietal functioning. Also, a significant positive relationship exists between lymph numbers and performance on a test of left temporoparietal functioning. Thus, some AD patients have greater immunological dysfunction based on relative left versus right temporoparietal functioning.

Functional MRI and structural MRI as tools for understanding comorbid conditions in children with epilepsy

Children with epilepsy are at risk for behavioral and cognitive comorbidities. Potential etiologies can be assessed in part by neuroimaging. Functional magnetic resonance imaging (MRI) has a major role in presurgical evaluation and prediction of postoperative outcome by mapping of language and memory. Structural MRI and functional MRI have shown changes in children and adolescents with attention deficit hyperactivity disorder and disruptive behavior, common comorbidities in children with epilepsy. Neuroimaging has the potential for significantly increasing understanding of the basis of cognitive and behavioral problems in children with epilepsy.

Hippocampal asymmetry: differences in structures and functions

The structural asymmetry of bilateral hippocampus in mammals has been well recognized. Recent findings highlighted the accompanying functional asymmetries, as well as the molecular differences of the hippocampus. The present paper summarized these recent advances in understanding the hippocampal asymmetries at molecular, circuit and functional levels. Additionally, the addition of new neurons to the hippocampal circuit during adulthood is asymmetrical. We conclude that these differences in molecules and structures of bilateral hippocampus determined the variances in functionality between the two sides.

The effects of temporal lobe epilepsy on scene encoding

Forty-four patients with temporal lobe epilepsy (TLE) (25 left) and 40 healthy control participants performed a complex visual scene-encoding fMRI task in a 4-T Varian scanner. Healthy controls and left temporal lobe epilepsy (LTLE) patients demonstrated symmetric activation during scene encoding. In contrast, right temporal lobe (RTLE) patients demonstrated left lateralization of scene encoding which differed significantly from healthy controls and LTLE patients (all p≤.05). Lateralization of scene encoding to the right hemisphere among LTLE patients was associated with inferior verbal memory performance as measured by neuropsychological testing (WMS-III Logical Memory Immediate, p = 0.049; WMS-III Paired Associates Immediate, p = 0.036; WMS-III Paired Associates Delayed, p = 0.047). In RTLE patients, left lateralization of scene encoding was associated with lower visuospatial memory performance (BVRT, p = 0.043) but improved verbal memory performance (WMS-III Word List, p = 0.049). These findings indicate that, despite the negative effects of epilepsy, memory functioning is better supported by the affected hemisphere than the hemisphere contralateral to the seizure focus.

The functional anatomy of non-verbal (pitch memory) function in left and right anterior temporal lobectomy patients

An fMRI pitch memory task was administered to left and right anterior temporal lobectomy (ATL) patients. The goal was to verify the neuroanatomical correlates of non-verbal memory, and to determine if pitch memory tasks can identify cognitive risk prior to ATL. The data showed that the bilateral posterior superior temporal lobes implement pitch memory in both ATL patients and NCs (normal controls), indicating that the task can be accomplished with either anterior temporal lobe resected. NCs activate the posterior temporal lobes more strongly than ATL patients during highly accurate performance. In contrast, both ATL groups activate the anterior cingulate in association with accuracy. While our data clarifies the functional neuroanatomy of pitch memory, it also indicates that such tasks do not serve well to lateralize and functionally map potentially "at risk" non-verbal memory skills prior to ATL.

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.

Topiramate and its effect on fMRI of language in patients with right or left temporal lobe epilepsy

Topiramate (TPM) is well recognized for its negative effects on cognition, language performance and lateralization results on the intracarotid amobarbital procedure (IAP). But, the effects of TPM on functional MRI (fMRI) of language and the fMRI signals are less clear. Functional MRI is increasingly used for presurgical evaluation of epilepsy patients in place of IAP for language lateralization. Thus, the goal of this study was to assess the effects of TPM on fMRI signals. In this study, we included 8 patients with right temporal lobe epilepsy (RTLE) and 8 with left temporal lobe epilepsy (LTLE) taking TPM (+TPM). Matched to them for age, handedness and side of seizure onset were 8 patients with RTLE and 8 with LTLE not taking TPM (-TPM). Matched for age and handedness to the patients with TLE were 32 healthy controls. The fMRI paradigm involved semantic decision/tone decision task (in-scanner behavioral data were collected). All epilepsy patients received a standard neuropsychological language battery. One sample t-tests were performed within each group to assess task-specific activations. Functional MRI data random-effects analysis was performed to determine significant group activation differences and to assess the effect of TPM dose on task activation. Direct group comparisons of fMRI, language and demographic data between patients with R/L TLE +TPM vs. -TPM and the analysis of the effects of TPM on blood oxygenation level-dependent (BOLD) signal were performed. Groups were matched for age, handedness and, within the R/L TLE groups, for the age of epilepsy onset/duration and the number of AEDs/TPM dose. The in-scanner language performance of patients was worse when compared to healthy controls - all p<0.044. While all groups showed fMRI activation typical for this task, regression analyses comparing L/R TLE +TPM vs. -TPM showed significant fMRI signal differences between groups (increases in left cingulate gyrus and decreases in left superior temporal gyrus in the patients with LTLE +TPM; increases in the right BA 10 and left visual cortex and decreases in the left BA 47 in +TPM RTLE). Further, TPM dose showed positive relationship with activation in the basal ganglia and negative associations with activation in anterior cingulate and posterior visual cortex. Thus, TPM appears to have a different effect on fMRI language distribution in patients with R/L TLE and a dose-dependent effect on fMRI signals. These findings may, in part, explain the negative effects of TPM on cognition and language performance and support the notion that TPM may affect the results of language fMRI lateralization/localization.

Neural stem cell grafting in an animal model of chronic temporal lobe epilepsy

Neural stem cell (NSC) transplantation into the hippocampus could offer an alternative therapy to hippocampal resection in patients with drug-resistant chronic epilepsy, which afflicts ∼30% of mesial temporal lobe epilepsy (TLE) cases. Multipotent, self-renewing NSCs could be expanded from multiple regions of the developing and adult brain, human embryonic stem cells (hESCs), and induced pluripotent stem cells (iPSCs). However, to provide a comprehensive methodology involved in testing the efficacy of transplantation of NSCs in a rat model of chronic TLE, NSCs derived from the embryonic medial ganglionic eminence (MGE) are taken as an example in this unit. The topics comprise description of the required materials, reagents and equipment, and protocols for expanding MGE-NSCs in culture, generating chronically epileptic rats, the intrahippocampal grafting, post-grafting evaluation of the effects of NSC grafts on spontaneous recurrent seizures and cognitive impairments, analyses of the yield and the fate of graft-derived cells, and the effects of NSC grafts on the host hippocampus.

Progress in cell grafting therapy for temporal lobe epilepsy

Temporal lobe epilepsy (TLE), exemplified by complex partial seizures, is recognized in ~30% of epileptic patients. Seizures in TLE are associated with cognitive dysfunction and are resistant to antiepileptic drug therapy in ~35% of patients. Although surgical resection of the hippocampus bestows improved seizure regulation in most cases of intractable TLE, this choice can cause lasting cognitive deficiency and reliance on antiepileptic drugs. Thus, alternative therapies that are proficient in both containing the spontaneous recurrent seizures and reversing the cognitive dysfunction are needed. The cell transplantation approach is promising in serving as an adept alternate therapy for TLE, because this strategy has shown the capability to curtail epileptogenesis when used soon after an initial precipitating brain injury, and to restrain spontaneous recurrent seizures and improve cognitive function when utilized after the occurrence of TLE. Nonetheless, this treatment needs further advancement and rigorous evaluation in animal prototypes of chronic TLE before the conceivable clinical use. It is especially vital to gauge the efficacy of distinct donor cell types, such as the hippocampal precursor cells, γ-aminobutyric acid-ergic progenitors, and neural stem cells derived from diverse human sources (including the embryonic stem cells and induced pluripotent stem cells) for longstanding seizure suppression using continuous electroencephalographic recordings for prolonged periods. Additionally, the identification of the mechanisms underlying the graft-mediated seizure suppression and improved cognitive function, and the development of apt grafting strategies that enhance the anti-seizure and pro-cognitive effects of grafts will be necessary. The goal of this review is to evaluate the progress made hitherto in this area and to discuss the prospect for cell-based therapy for TLE.

Promise of resveratrol for easing status epilepticus and epilepsy

Resveratrol (RESV; 3,5,4'-tri-hydroxy stilbene), a naturally occurring phytoalexin, is found at a high concentration in the skin of red grapes and red wine. RESV mediates a wide-range of biological activities, which comprise an increased life span, anti-ischemic, anti-cancer, antiviral, anti-aging and anti-inflammatory properties. Studies in several animal prototypes of brain injury suggest that RESV is an effective neuroprotective compound. Ability to enter the brain after a peripheral administration and no adverse effects on the brain or body are other features that are appealing for using this compound as a therapy for brain injury or neurodegenerative diseases. The goal of this review is to discuss the promise of RESV for treating acute seizures, preventing the acute seizure or status epilepticus induced development of chronic epilepsy, and easing the chronic epilepsy typified by spontaneous recurrent seizures and cognitive dysfunction. First, the various beneficial effects of RESV on the normal brain are discussed to provide a rationale for considering RESV treatment in the management of acute seizures and epilepsy. Next, the detrimental effects of acute seizures or status epilepticus on the hippocampus and the implications of post-status epilepticus changes in the hippocampus towards the occurrence of chronic epilepsy and cognitive dysfunction are summarized. The final segment evaluates studies that have used RESV as a neuroprotective compound against seizures, and proposes studies that are critically needed prior to the clinical application of RESV as a prophylaxis against the development of chronic epilepsy and cognitive dysfunction after an episode of status epilepticus or head injury.

Update on neuroimaging in epilepsy

Neuroimaging in epilepsy is a very large and growing field. Researchers in this area have quickly adopted new methods, resulting in a lively literature. Basic features of common epilepsies are well known, but, outside of the specific area of epilepsy surgery evaluation, new methods evolving in the last few years have had limited new beneficial clinical impact. Here, an overview of the epilepsy neuroimaging literature of the last 5 years, with an emphasis on mesial temporal lobe epilepsy, idiopathic generalized epilepsies, presurgical evaluation and new developments in functional MRI is presented. The need for attention to clinical translation, as well as immediate opportunities and future trends in this field, are discussed.

Functional MRI in chronic epilepsy: associations with cognitive impairment

Chronic epilepsy is frequently accompanied by serious cognitive side-effects. Clinical factors are important, but cannot account entirely for this cognitive comorbidity. Therefore, research is focusing on the underlying cerebral mechanisms to understand the development of cognitive dysfunction. In the past two decades, functional MRI techniques have been applied extensively to the study of cognitive impairment in chronic epilepsy. However, because of wide variation in study designs, analysis methods, and data presentation, interpretation of these studies has become increasingly difficult for clinicians. In patients with localisation-related epilepsy, whether findings of functional MRI represent the underlying neuronal substrate for cognitive decline remains a subject of debate.

Current themes in neuroimaging of epilepsy: brain networks, dynamic phenomena, and clinical relevance

Brain scanning methods were first applied in patients with epilepsy more than 30years ago. A very substantial literature now exists in this field, which is exponentially increasing. Contemporary neuroimaging studies in epilepsy reflect new concepts in the epilepsies, as well as current methodological developments. In particular, this area is emphasising the role of networks in epileptogenicity, the existence of dynamic phenomena which can be captured by imaging, and is beginning to validate the implementation of neuroimaging in the clinic. Here, recent studies of the last 5years are reviewed, covering the full range of neuroimaging methods with SPECT, PET and MRI in epilepsy.

Functional and structural changes in the memory network associated with left temporal lobe epilepsy

Understanding functional plasticity in memory networks associated with temporal lobe epilepsy (TLE) is central to predicting memory decline following surgery. However, the extent of functional reorganization within memory networks remains unclear. In this preliminary study, we used novel analysis methods assessing network-level changes across the brain during memory task performance in patients with TLE to test the hypothesis that hippocampal functions may not readily shift between hemispheres, but instead may show altered intra-hemispheric organization with unilateral damage. In addition, we wished to relate functional differences to structural changes along specific fibre pathways associated with memory function. Nine pre-operative patients with intractable left TLE and 10 healthy controls underwent functional MRI during complex scene encoding. Diffusion tensor imaging was additionally performed in the same patients. In our study, we found no evidence of inter-hemispheric shifts in memory-related activity in TLE using standard general linear model analysis. However, tensor independent component analysis revealed significant reductions in functional connectivity between bilateral MTL, occipital and left orbitofrontal regions among others in left TLE. This altered orbitofrontal activity was directly related to measures of fornix tract coherence in patients (P < 0.05). Our results suggest that specific fibre pathways, potentially affected by MTL neurodegeneration, may play a central role in functional plasticity in TLE and highlight the importance of network-based analysis approaches. Relative to standard model-based methods, novel objective functional connectivity analyses may offer improved sensitivity to subtle changes in the distribution of memory functions relevant for surgical planning in TLE.

Biomagnetic profiles of verbal memory success in patients with mesial temporal lobe epilepsy

The risk of cognitive decline after mesial temporal lobe (MTL) resection in the dominant hemisphere for treatment of epilepsy has been assessed with the intracarotid amytal procedure and functional neuroimaging. In this study we used magnetoencephalography (MEG) to analyze memory profiles in patients with left hippocampal sclerosis (HS). Biomagnetic brain activity related to successful memory was compared in nine patients with left HS and nine age-matched controls. Patients manifested a higher number of activity sources over the right inferior parietal lobe in the late portion of the time window, and higher activity in the right than in the left MTL between 400 and 800 ms. This was reinforced by a -0.46 MTL laterality index, which indicates right MTL dominance. Controls showed a higher number of dipoles in the left anterior ventral prefrontal region, between 400 and 600 ms, and in the left MTL across the whole time window. Three patients who underwent a left temporal lobectomy, were seizure free, and who did not exhibit memory impairment after left temporal lobectomy, showed no activity in the left MTL presurgically. These results could support the ability of MEG to describe the time-modulated brain activity related to memory success in patients with epilepsy with left HS.

Memory performance is related to language dominance as determined by the intracarotid amobarbital procedure

OBJECTIVE

The goal of this study was to explore the relationship between language and memory lateralization in patients with epilepsy undergoing the intracarotid amobarbital procedure.

METHODS

In 386 patients, language lateralization and memory lateralization as determined by laterality index (LI) were correlated with each other.

RESULTS

Language lateralization and memory lateralization were positively correlated (r=0.34, P<0.01). Correlations differed depending on the presence and type of lesion (chi(2)=7.98, P<0.05). LIs correlated significantly higher (z=2.82, P<0.05) in patients with cortical dysplasia (n=41, r=0.61, P<0.01) compared with the group without lesions (n=90, r=0.16, P>0.05), with patients with hippocampal sclerosis falling between these two groups. Both memory (P<0.01) and language (P<0.01) LIs were higher in right- compared with left-sided lesions.

CONCLUSION

Correlation of language and memory is more pronounced in patients with structural lesions as compared with patients without lesions on MRI.

Impaired perceptual networks in temporal lobe epilepsy revealed by resting fMRI

Viewed as a neural network disorder, mesial temporal lobe epilepsy (mTLE) may cause widespread deficits in human brain functions. Impairments in cognitive functions such as memory and language have been well addressed, but perceptual deficits have only been considered in terms of behavioral data. Little imaging research on perceptual deficits in mTLE has been reported. The present study is expected to reveal impairments in the perceptual networks in patients with mTLE using fMRI. The fMRI-based independent component analysis (ICA) was applied to 33 patients with mTLE and 33 matched healthy controls. In light of the resting-state networks (RSNs) corresponding to the basal functions of visual, auditory, and sensorimotor systems, the ICA data of functional connectivity within these RSNs were compared between the patients and controls. Compared with the controls, the mTLE patients presented decreased functional connectivity within the regions of the auditory and sensorimotor networks, as well increased functional connectivity in the primary visual cortex and decreased functional connectivity in the bilateral MT+ areas of the visual network. Our neuroimaging results are in agreement with the previous findings that specific perceptual functions are impaired in mTLE. Furthermore, our findings in the visual network support the belief that the primary visual function is not impaired and that there may be deficits in the high-order visual function in mTLE. Our fMRI study may contribute to the understanding of neuropathophysiological mechanisms underlying perceptual impairments in mTLE.

Compensatory brain activation for recognition memory in patients with medication-resistant epilepsy

Progressive decline of memory functions has been observed in patients with chronic medication-resistant epilepsy. The progression likely relates to the effects of epileptiform discharges, seizures, and medications on the processes of encoding and retrieval. The goal of the study described here was to use functional MRI (fMRI) to examine the effects of chronic epilepsy on verbal recognition memory. We enrolled 12 patients with medication-resistant epilepsy (5 with right and 7 with left hemispheric seizure onset) and 18 healthy controls matched for age, gender, and handedness. Subjects underwent fMRI at 3T using a word recognition task during which they had to recall if words presented during scanning were words they had learned prior to scanning. Although we noted many similarities in the fMRI activation patterns between the subjects with epilepsy and the healthy subjects in areas typically involved in memory processing, testing of the interaction effects for target-foil differences between groups revealed several differences in activation including the right insula, the left cuneus, and the bilateral subgenual anterior cingulate cortex (ACC). In patients with epilepsy, these regions exhibited greater activation for targets than foils, but in healthy subjects the difference was reversed (right insula), absent (left cuneus), or included deactivation to target words (pregenual ACC). These differences were seen despite similar performance during the memory task, suggesting that activations observed in these additional regions may represent compensatory processes for verbal recognition memory that are induced by chronic brain injury related to recurrent seizures.

Does clinical memory fMRI provide a comprehensive map of medial temporal lobe structures?

Successful clinical application of fMRI tasks requires reliable knowledge about the brain structures mapped by the task. With memory fMRI, diverging evidence exists concerning the location of major signal sources as well as hippocampal contributions. To clarify these issues, we investigated a frequently applied memory test (home town walking) in 33 patients with unilateral medial temporal lobe pathology, comparing healthy and diseased hemispheres. We focused on a detailed investigation of individual fMRI maps on non-transformed high-resolution functional images. Results show a clear dominance of activations around the collateral sulcus, corresponding to parahippocampal and entorhinal cortex activities. Hippocampus activity was absent in the vast majority of patients. The diseased hemispheres showed lower activation than the healthy hemispheres. We conclude that (1) the investigated memory test may be successfully applied for evaluation of the parahippocampal cortex, (2) the hippocampus is not reliably mapped by the task, and (3) the methods described for investigation of individual high-resolution functional images allow generation of application profiles for clinical fMRI tasks.