Edge-wise analysis reveals white matter connectivity associated with focal to bilateral tonic-clonic seizures

OBJECTIVE

Focal to bilateral tonic-clonic seizures (FBTCS) represent a challenging subtype of focal temporal lobe epilepsy (TLE) in terms of both severity and treatment response. Most studies have focused on regional brain analysis that is agnostic to the distribution of white matter (WM) pathways associated with a node. We implemented a more selective, edge-wise approach that allowed for identification of the individual connections unique to FBTCS.

METHODS

T1-weighted and diffusion-weighted images were obtained from 22 patients with solely focal seizures (FS), 43 FBTCS patients, and 65 age/sex-matched healthy participants (HPs), yielding streamline (STR) connectome matrices. We used diffusion tensor-derived STRs in an edge-wise approach to determine specific structural connectivity changes associated with seizure generalization in FBTCS compared to matched FS and HPs. Graph theory metrics were computed on both node- and edge-based connectivity matrices.

RESULTS

Edge-wise analyses demonstrated that all significantly abnormal cross-hemispheric connections belonged to the FBTCS group. Abnormal connections associated with FBTCS were mostly housed in the contralateral hemisphere, with graph metric values generally decreased compared to HPs. In FBTCS, the contralateral amygdala showed selective decreases in the structural connection pathways to the contralateral frontal lobe. Abnormal connections in TLE involved the amygdala, with the ipsilateral side showing increases and the contralateral decreases. All the FS findings indicated higher graph metrics for connections involving the ipsilateral amygdala. Data also showed that some FBTCS connectivity effects are moderated by aging, recent seizure frequency, and longer illness duration.

SIGNIFICANCE

Data showed that not all STR pathways are equally affected by the seizure propagation of FBTCS. We demonstrated two key biases, one indicating a large role for the amygdala in the propagation of seizures, the other pointing to the prominent role of cross-hemispheric and contralateral hemisphere connections in FBTCS. We demonstrated topographic reorganization in FBTCS, pointing to the specific WM tracts involved.

Pre-surgical features of intrinsic brain networks predict single and joint epilepsy surgery outcomes

Despite the effectiveness of surgical interventions for the treatment of intractable focal temporal lobe epilepsy (TLE), the substrates that support good outcomes are poorly understood. While algorithms have been developed for the prediction of either seizure or cognitive/psychiatric outcomes alone, no study has reported on the functional and structural architecture that supports joint outcomes. We measured key aspects of pre-surgical whole brain functional/structural network architecture and evaluated their ability to predict post-operative seizure control in combination with cognitive/psychiatric outcomes. Pre-surgically, we identified the intrinsic connectivity networks (ICNs) unique to each person through independent component analysis (ICA), and computed: (1) the spatial-temporal match between each person's ICA components and established, canonical ICNs, (2) the connectivity strength within each identified person-specific ICN, (3) the gray matter (GM) volume underlying the person-specific ICNs, and (4) the amount of variance not explained by the canonical ICNs for each person. Post-surgical seizure control and reliable change indices of change (for language [naming, phonemic fluency], verbal episodic memory, and depression) served as binary outcome responses in random forest (RF) models. The above functional and structural measures served as input predictors. Our empirically derived ICN-based measures customized to the individual showed that good joint seizure and cognitive/psychiatric outcomes depended upon higher levels of brain reserve (GM volume) in specific networks. In contrast, singular outcomes relied on systematic, idiosyncratic variance in the case of seizure control, and the weakened pre-surgical presence of functional ICNs that encompassed the ictal temporal lobe in the case of cognitive/psychiatric outcomes. Our data made clear that the ICNs differed in their propensity to provide reserve for adaptive outcomes, with some providing structural (brain), and others functional (cognitive) reserve. Our customized methodology demonstrated that when substantial unique, patient-specific ICNs are present prior to surgery there is a reliable association with poor post-surgical seizure control. These ICNs are idiosyncratic in that they did not match the canonical, normative ICNs and, therefore, could not be defined functionally, with their location likely varying by patient. This important finding suggested the level of highly individualized ICN's in the epileptic brain may signal the emergence of epileptogenic activity after surgery.

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

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

Uncovering the biological basis of control energy: Structural and metabolic correlates of energy inefficiency in temporal lobe epilepsy

Network control theory is increasingly used to profile the brain's energy landscape via simulations of neural dynamics. This approach estimates the control energy required to simulate the activation of brain circuits based on structural connectome measured using diffusion magnetic resonance imaging, thereby quantifying those circuits' energetic efficiency. The biological basis of control energy, however, remains unknown, hampering its further application. To fill this gap, investigating temporal lobe epilepsy as a lesion model, we show that patients require higher control energy to activate the limbic network than healthy volunteers, especially ipsilateral to the seizure focus. The energetic imbalance between ipsilateral and contralateral temporolimbic regions is tracked by asymmetric patterns of glucose metabolism measured using positron emission tomography, which, in turn, may be selectively explained by asymmetric gray matter loss as evidenced in the hippocampus. Our investigation provides the first theoretical framework unifying gray matter integrity, metabolism, and energetic generation of neural dynamics.

Multiple-brain systems dynamically interact during tonic and phasic states to support language integrity in temporal lobe epilepsy

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Unique brain dynamics occur during language task in left temporal lobe epilepsy (TLE).

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Multiple brain systems interact to implement compensated language status in TLE.

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Tonic/rest dynamics exert influence and may prime the level of phasic/task dynamics.

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Multi-network integrations are compensatory in patients with lower language skills.

An epileptogenic focus in the dominant temporal lobe can result in the reorganization of language systems in order to compensate for compromised functions. We studied the compensatory reorganization of language in the setting of left temporal lobe epilepsy (TLE), taking into account the interaction of language (L) with key non-language (NL) networks such as dorsal attention (DAN), fronto-parietal (FPN) and cingulo-opercular (COpN), with these systems providing cognitive resources helpful for successful language performance.

We applied tools from dynamic network neuroscience to functional MRI data collected from 23 TLE patients and 23 matched healthy controls during the resting state (RS) and a sentence completion (SC) task to capture how the functional architecture of a language network dynamically changes and interacts with NL systems in these two contexts.

We provided evidence that the brain areas in which core language functions reside dynamically interact with non-language functional networks to carry out linguistic functions. We demonstrated that abnormal integrations between the language and DAN existed in TLE, and were present both in tonic as well as phasic states. This integration was considered to reflect the entrainment of visual attention systems to the systems dedicated to lexical semantic processing. Our data made clear that the level of baseline integrations between the language subsystems and certain NL systems (e.g., DAN, FPN) had a crucial influence on the general level of task integrations between L/NL systems, with this a normative finding not unique to epilepsy. We also revealed that a broad set of task L/NL integrations in TLE are predictive of language competency, indicating that these integrations are compensatory for patients with lower overall language skills.

We concluded that RS establishes the broad set of L/NL integrations available and primed for use during task, but that the actual use of those interactions in the setting of TLE depended on the level of language skill. We believe our analyses are the first to capture the potential compensatory role played by dynamic network reconfigurations between multiple brain systems during performance of a complex language task, in addition to testing for characteristics in both the phasic/task and tonic/resting state that are necessary to achieve language competency in the setting of temporal lobe pathology. Our analyses highlighted the intra- versus inter-system communications that form the basis of unique language processing in TLE, pointing to the dynamic reconfigurations that provided the broad multi-system support needed to maintain language skill and competency.

Computational support, not primacy, distinguishes compensatory memory reorganization in epilepsy

Temporal lobe epilepsy is associated with impairment in episodic memory. A substantial subgroup, however, is able to maintain adequate memory despite temporal lobe pathology. Missing from prior work in cognitive reorganization is a direct comparison of temporal lobe epilepsy patients with intact status with those who are memory impaired. Little is known about the regional activations, functional connectivities and/or network reconfigurations that implement changes in primary computations or support functions that drive adaptive plasticity and compensated memory. We utilized task functional MRI on 54 unilateral temporal lobe epilepsy patients and 24 matched healthy controls during the performance of a paired-associate memory task to address three questions: (i) which regions implement paired-associate memory in temporal lobe epilepsy, and do they vary as a function of good versus poor performance, (ii) is there unique functional connectivity present during memory encoding that accounts for intact status by preservation of primary memory computations or the supportive computations that allow for intact memory responses and (iii) what features during memory encoding are most distinctive: is it the magnitude and location of regional activations, or the presence of enhanced functional connections to key structures such as the hippocampus? The study revealed non-dominant hemisphere regions (right posterior temporal regions) involving both increased regional activity and increased modulatory communication with the hippocampi as most important to intact memory in left temporal lobe epilepsy compared to impaired status. The profile involved areas that are neither contralateral homologues to left hemisphere memory areas, nor regions traditionally considered computationally primary for episodic memory. None of these areas of increased activation or functional connectivity were associated with advantaged memory in healthy controls. Our emphasis on different performance levels yielded insight into two forms of cognitive reorganization: computational primacy, where left temporal lobe epilepsy showed little change relative to healthy controls, and computational support where intact left temporal lobe epilepsy patients showed adaptive abnormalities. The analyses isolated the unique regional activations and mediating functional connectivity that implements truly compensatory reorganization in left temporal lobe epilepsy. The results provided a new perspective on memory deficits by making clear that they arise not just from the knockout of a functional hub, but from the failure to instantiate a complex set of reorganization responses. Such responses provided the computational support to ensure successful memory. We demonstrated that by keeping track of performance levels, we can increase understanding of adaptive brain responses and neuroplasticity in epilepsy.

Disrupted basal ganglia-thalamocortical loops in focal to bilateral tonic-clonic seizures

Focal to bilateral tonic-clonic seizures are associated with lower quality of life, higher risk of seizure-related injuries, increased chance of sudden unexpected death, and unfavourable treatment outcomes. Achieving greater understanding of their underlying circuitry offers better opportunity to control these seizures. Towards this goal, we provide a network science perspective of the interactive pathways among basal ganglia, thalamus and cortex, to explore the imprinting of secondary seizure generalization on the mesoscale brain network in temporal lobe epilepsy. Specifically, we parameterized the functional organization of both the thalamocortical network and the basal ganglia-thalamus network with resting state functional MRI in three groups of patients with different focal to bilateral tonic-clonic seizure histories. Using the participation coefficient to describe the pattern of thalamocortical connections among different cortical networks, we showed that, compared to patients with no previous history, those with positive histories of focal to bilateral tonic-clonic seizures, including both remote (none for >1 year) and current (within the past year) histories, presented more uniform distribution patterns of thalamocortical connections in the ipsilateral medial-dorsal thalamic nuclei. As a sign of greater thalamus-mediated cortico-cortical communication, this result comports with greater susceptibility to secondary seizure generalization from the epileptogenic temporal lobe to broader brain networks in these patients. Using interregional integration to characterize the functional interaction between basal ganglia and thalamus, we demonstrated that patients with current history presented increased interaction between putamen and globus pallidus internus, and decreased interaction between the latter and the thalamus, compared to the other two patient groups. Importantly, through a series of 'disconnection' simulations, we showed that these changes in interactive profiles of the basal ganglia-thalamus network in the current history group mainly depended upon the direct but not the indirect basal ganglia pathway. It is intuitively plausible that such disruption in the striatum-modulated tonic inhibition of the thalamus from the globus pallidus internus could lead to an under-suppressed thalamus, which in turn may account for their greater vulnerability to secondary seizure generalization. Collectively, these findings suggest that the broken balance between basal ganglia inhibition and thalamus synchronization can inform the presence and effective control of focal to bilateral tonic-clonic seizures. The mechanistic underpinnings we uncover may shed light on the development of new treatment strategies for patients with temporal lobe epilepsy.

Tonic Resting State Hubness Supports High Gamma Activity Defined Verbal Memory Encoding Network in Epilepsy

High gamma activity (HGA) of verbal-memory encoding using invasive-electroencephalogram has laid the foundation for numerous studies testing the integrity of memory in diseased populations. Yet, the functional connectivity characteristics of networks subserving these memory linkages remains uncertain. By integrating this electrophysiological biomarker of memory encoding from IEEG with resting-state BOLD fluctuations, we estimated the segregation and hubness of HGA-memory regions in drug-resistant epilepsy patients and matched healthy controls. HGA-memory regions express distinctly different hubness compared to neighboring regions in health and in epilepsy, and this hubness was more relevant than segregation in predicting verbal memory encoding. The HGA-memory network comprised regions from both the cognitive control and primary processing networks, validating that effective verbal-memory encoding requires integrating brain functions, and is not dominated by a central cognitive core. Our results demonstrate a tonic intrinsic set of functional connectivity, which provides the necessary conditions for effective, phasic, task-dependent memory encoding.

Disrupted dynamic network reconfiguration of the language system in temporal lobe epilepsy

Temporal lobe epilepsy tends to reshape the language system causing maladaptive reorganization that can be characterized by task-based functional MRI, and eventually can contribute to surgical decision making processes. However, the dynamic interacting nature of the brain as a complex system is often neglected, with many studies treating the language system as a static monolithic structure. Here, we demonstrate that as a specialized and integrated system, the language network is inherently dynamic, characterized by rich patterns of regional interactions, whose transient dynamics are disrupted in patients with temporal lobe epilepsy. Specifically, we applied tools from dynamic network neuroscience to functional MRI data collected from 50 temporal lobe epilepsy patients and 30 matched healthy controls during performance of a verbal fluency task, as well as during rest. By assigning 16 language-related regions into four subsystems (i.e. bilateral frontal and temporal), we observed regional specialization in both the probability of transient interactions and the frequency of such changes, in both healthy controls and patients during task performance but not rest. Furthermore, we found that both left and right temporal lobe epilepsy patients displayed reduced interactions within the left frontal 'core' subsystem compared to the healthy controls, while left temporal lobe epilepsy patients were unique in showing enhanced interactions between the left frontal 'core' and the right temporal subsystems. Also, both patient groups displayed reduced flexibility in the transient interactions of the left temporal and right frontal subsystems, which formed the 'periphery' of the language network. Importantly, such group differences were again evident only during task condition. Lastly, through random forest regression, we showed that dynamic reconfiguration of the language system tracks individual differences in verbal fluency with superior prediction accuracy compared to traditional activation-based static measures. Our results suggest dynamic network measures may be an effective biomarker for detecting the language dysfunction associated with neurological diseases such as temporal lobe epilepsy, specifying both the type of neuronal communications that are missing in these patients and those that are potentially added but maladaptive. Further advancements along these lines, transforming how we characterize and map language networks in the brain, have a high probability of altering clinical decision making in neurosurgical centres.10.1093/brain/awy042_video1awy042media15754656112001.

Functional control of electrophysiological network architecture using direct neurostimulation in humans

Chronically implantable neurostimulation devices are becoming a clinically viable option for treating patients with neurological disease and psychiatric disorders. Neurostimulation offers the ability to probe and manipulate distributed networks of interacting brain areas in dysfunctional circuits. Here, we use tools from network control theory to examine the dynamic reconfiguration of functionally interacting neuronal ensembles during targeted neurostimulation of cortical and subcortical brain structures. By integrating multimodal intracranial recordings and diffusion-weighted imaging from patients with drug-resistant epilepsy, we test hypothesized structural and functional rules that predict altered patterns of synchronized local field potentials. We demonstrate the ability to predictably reconfigure functional interactions depending on stimulation strength and location. Stimulation of areas with structurally weak connections largely modulates the functional hubness of downstream areas and concurrently propels the brain towards more difficult-to-reach dynamical states. By using focal perturbations to bridge large-scale structure, function, and markers of behavior, our findings suggest that stimulation may be tuned to influence different scales of network interactions driving cognition.

Brain stimulation devices capable of perturbing the physiological state of neural systems are rapidly gaining popularity for their potential to treat neurological and psychiatric disease. A root problem is that underlying dysfunction spans a large-scale network of brain regions, requiring the ability to control the complex interactions between multiple brain areas. Here, we use tools from network control theory to examine the dynamic reconfiguration of functionally interacting neuronal ensembles during targeted neurostimulation of cortical and subcortical brain structures. We demonstrate the ability to predictably reconfigure patterns of interactions between functional brain areas by modulating the strength and location of stimulation. Our findings have high significance for designing stimulation protocols capable of modulating distributed neural circuits in the human brain.

Neuroimaging and connectomics of drug-resistant epilepsy at multiple scales: From focal lesions to macroscale networks

Epilepsy is among the most common chronic neurologic disorders, with 30%-40% of patients having seizures despite antiepileptic drug treatment. The advent of brain imaging and network analyses has greatly improved the understanding of this condition. In particular, developments in magnetic resonance imaging (MRI) have provided measures for the noninvasive characterization and detection of lesions causing epilepsy. MRI techniques can probe structural and functional connectivity, and network analyses have shaped our understanding of whole-brain anomalies associated with focal epilepsies. This review considers the progress made by neuroimaging and connectomics in the study of drug-resistant epilepsies due to focal substrates, particularly temporal lobe epilepsy related to mesiotemporal sclerosis and extratemporal lobe epilepsies associated with malformations of cortical development. In these disorders, there is evidence of widespread disturbances of structural and functional connectivity that may contribute to the clinical and cognitive prognosis of individual patients. It is hoped that studying the interplay between macroscale network anomalies and lesional profiles will improve our understanding of focal epilepsies and assist treatment choices.

Enhanced co-registration methods to improve intracranial electrode contact localization

Background

Electrode contact locations are important when planning tailored brain surgeries to identify pathological tissue targeted for resection and conversely avoid eloquent tissue. Current methods employ trained experts to use neuroimaging scans that are manually co-registered and localize contacts within ~2 mm. Yet, the state of the art is limited by either the expertise needed for each type of intracranial electrode or the inter-modality co-registration which increases error, reducing accuracy. Patients often have a variety of strips, grids and depths implanted; therefore, it is cumbersome and time-consuming to apply separate localization methods for each type of electrode, requiring expertise across different approaches.

New method

To overcome these limitations, a computational method was developed by separately registering an implant magnetic resonance image (MRI) and implant computed tomography image (CT) to the pre-implant MRI, then calculating an iterative closest point transformation using the contact locations extracted from the signal voids as ground truth.

Results

The implant MRI is robustly co-registered to the pre-implant MRI with a boundary-based registration algorithm. By extracting and utilizing ‘signal voids’ (the metal induced artifacts from the implant MRI) as electrode fiducials, the novel method is an all-in-one approach for all types of intracranial electrodes while eliminating inter-modality co-registration errors.

Comparison with existing methods

The distance between each electrode centroid and the brain's surface was measured, for the proposed method as well as the state of the art method using two available software packages, SPM 12 and FSL 4.1. The method presented here achieves the smallest distances to the brain's surface for all strip and grid type electrodes, i.e. contacts designed to rest directly on the brain surface.

Conclusion

We use one of the largest reported sample sizes in localization studies to validate this novel method for localizing different kinds of intracranial electrodes including grids, strips and depth electrodes.

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Co-registration between intramodal pre- and implant images allows for accurate localization of all subdural electrode types.

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Iterative closest point (ICP) assisted grid electrode localization is comparable to existing implant MRI based methods.

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ICP is a novel, semi-automated method to localize grid, strip and depth electrodes with state-of-the-art accuracy

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.

Presurgical thalamic "hubness" predicts surgical outcome in temporal lobe epilepsy

OBJECTIVE

To characterize the presurgical brain functional architecture presented in patients with temporal lobe epilepsy (TLE) using graph theoretical measures of resting-state fMRI data and to test its association with surgical outcome.

METHODS

Fifty-six unilateral patients with TLE, who subsequently underwent anterior temporal lobectomy and were classified as obtaining a seizure-free (Engel class I, n = 35) vs not seizure-free (Engel classes II-IV, n = 21) outcome at 1 year after surgery, and 28 matched healthy controls were enrolled. On the basis of their presurgical resting-state functional connectivity, network properties, including nodal hubness (importance of a node to the network; degree, betweenness, and eigenvector centralities) and integration (global efficiency), were estimated and compared across our experimental groups. Cross-validations with support vector machine (SVM) were used to examine whether selective nodal hubness exceeded standard clinical characteristics in outcome prediction.

RESULTS

Compared to the seizure-free patients and healthy controls, the not seizure-free patients displayed a specific increase in nodal hubness (degree and eigenvector centralities) involving both the ipsilateral and contralateral thalami, contributed by an increase in the number of connections to regions distributed mostly in the contralateral hemisphere. Simulating removal of thalamus reduced network integration more dramatically in not seizure-free patients. Lastly, SVM models built on these thalamic hubness measures produced 76% prediction accuracy, while models built with standard clinical variables yielded only 58% accuracy (both were cross-validated).

CONCLUSIONS

A thalamic network associated with seizure recurrence may already be established presurgically. Thalamic hubness can serve as a potential biomarker of surgical outcome, outperforming the clinical characteristics commonly used in epilepsy surgery centers.

From "rest" to language task: Task activation selects and prunes from broader resting-state network

Resting-state networks (RSNs) show spatial patterns generally consistent with networks revealed during cognitive tasks. However, the exact degree of overlap between these networks has not been clearly quantified. Such an investigation shows promise for decoding altered functional connectivity (FC) related to abnormal language functioning in clinical populations such as temporal lobe epilepsy (TLE). In this context, we investigated the network configurations during a language task and during resting state using FC. Twenty-four healthy controls, 24 right and 24 left TLE patients completed a verb generation (VG) task and a resting-state fMRI scan. We compared the language network revealed by the VG task with three FC-based networks (seeding the left inferior frontal cortex (IFC)/Broca): two from the task (ON, OFF blocks) and one from the resting state. We found that, for both left TLE patients and controls, the RSN recruited regions bilaterally, whereas both VG-on and VG-off conditions produced more left-lateralized FC networks, matching more closely with the activated language network. TLE brings with it variability in both task-dependent and task-independent networks, reflective of atypical language organization. Overall, our findings suggest that our RSN captured bilateral activity, reflecting a set of prepotent language regions. We propose that this relationship can be best understood by the notion of pruning or winnowing down of the larger language-ready RSN to carry out specific task demands. Our data suggest that multiple types of network analyses may be needed to decode the association between language deficits and the underlying functional mechanisms altered by disease. Hum Brain Mapp 38:2540-2552, 2017. © 2017 Wiley Periodicals, Inc.

Neuro emotional technique effects on brain physiology in cancer patients with traumatic stress symptoms: preliminary findings

PURPOSE

The purpose of this study was to characterize the neurophysiological and clinical effects that may result from the neuro emotional technique (NET) in patients with traumatic stress symptoms associated with a cancer-related event. We hypothesized that self-regulatory processing of traumatic memories would be observable as physiological changes in key brain areas after undergoing the NET intervention and that these changes would be associated with improvement of traumatic stress symptoms.

METHODS

We enrolled 23 participants with a prior cancer diagnosis who expressed a distressing cancer-related memory that was associated with traumatic stress symptoms of at least 6 months in duration. Participants were randomized to either the NET intervention or a waitlist control condition. To evaluate the primary outcome of neurophysiological effects, all participants received functional magnetic resonance imaging (fMRI) during the auditory presentation of both a neutral stimulus and a description of the specific traumatic event. Pre/post-comparisons were performed between the traumatic and neutral condition, within and between groups. Psychological measures included the Impact of Event Scale (IES), State Trait Anxiety Index (STAI), Brief Symptom Inventory (BSI)-18, and Posttraumatic Cognitions Inventory (PTCI).

RESULTS

The initial fMRI scans in both groups showed significant increases in the bilateral parahippocampus and brainstem. After NET, reactivity in the parahippocampus, brainstem, anterior cingulate, and insula was significantly decreased during the traumatic stimulus. Likewise, participants receiving the NET intervention had significant reductions (p < 0.05) compared to the control group in distress as measured by the BSI-18 global severity index, anxiety as measured by the STAI, and traumatic stress as measured by the IES and PTCI.

CONCLUSIONS

This study is an initial step towards understanding mechanistic features of the NET intervention. Specifically, brain regions involved with traumatic memories and distress such as the brainstem, insula, anterior cingulate gyrus, and parahippocampus had significantly reduced activity after the NET intervention and were associated with clinical improvement of symptoms associated with distressing recollections.

IMPLICATIONS FOR CANCER SURVIVORS

This preliminary study suggests that the NET intervention may be effective at reducing emotional distress in patients who suffer from traumatic stress symptoms associated with a cancer-related event.

The Temporal Instability of Resting State Network Connectivity in Intractable Epilepsy

OBJECTIVE

Focal epilepsies, such as temporal lobe epilepsy (TLE), are known to disrupt network activity in areas outside the epileptogenic zone [Tracy et al., 2015]. We devised a measure of temporal instability of resting state functional connectivity (FC), capturing temporal variations of BOLD correlations between brain regions that is less confounded than the "sliding window" approach common in the literature.

METHODS

We investigated healthy controls and unilateral TLE patients (right and left seizure focus groups), utilizing group ICA to identify the default mode network (DMN), a network associated with episodic memory, a key cognitive deficit in TLE. Our instability analyses focused on: (1) connectivity between DMN region pairs, both within and between TLE patients and matched controls, (2) whole brain group differences between region pairs ipsilateral or contralateral to the epileptogenic temporal lobe.

RESULTS

For both the whole brain and a more focused analysis of DMN region pairs, temporal stability appears to characterize the healthy brain. The TLE patients displayed more FC instability compared to controls, with this instability more pronounced for the right TLE patients.

SIGNIFICANCE

Our findings challenge the view that the resting state signal is stable over time, providing a measure of signal coherence change that may generate insights into the temporal components of network organization. The precuneus was the region within the DMN consistently expressing this instability, suggesting this region plays a key role in large scale temporal dynamics of the DMN, with such dynamics disrupted in TLE, putting key cognitive functions at risk. Hum Brain Mapp 38:528-540, 2017. © 2016 Wiley Periodicals, Inc.

Learning Complex Categories Two Ways at Once: The Link between Automatic Processing and Nonanalytic Learning

Concurrent automatic and focal attentive processes were evaluated for a categorization task. Automatic processing is associated with nonanalytic processing and is less deliberate, effortful, and less strategy based. Automatic processing does not interfere with focal attentive processing. This set of facts yielded two hypotheses, that automatic learning of categories would occur concurrently with focal attentive learning of categories and automatic learning of categories would be nonanalytic. After a phase of self-paced learning, analytic categorizers were identified. These analytic subjects proceeded to a speeded categorization task and were tested for evidence of a shift toward nonanalytic learning. A significant increase in nonanalytic responses was found in the speeded condition, providing modest support for the hypotheses.

Gray Matter Abnormalities in Temporal Lobe Epilepsy: Relationships with Resting-State Functional Connectivity and Episodic Memory Performance

Temporal lobe epilepsy (TLE) affects multiple brain regions through evidence from both structural (gray matter; GM) and functional connectivity (FC) studies. We tested whether these structural abnormalities were associated with FC abnormalities, and assessed the ability of these measures to explain episodic memory impairments in this population. A resting-state and T1 sequences were acquired on 94 (45 with mesial temporal pathology) TLE patients and 50 controls, using magnetic resonance imaging (MRI) technique. A voxel-based morphometry analysis was computed to determine the GM volume differences between groups (right, left TLE, controls). Resting-state FC between the abnormal GM volume regions was computed, and compared between groups. Finally, we investigated the relation between EM, GM and FC findings. Patients with and without temporal pathology were analyzed separately. The results revealed reduced GM volume in multiple regions in the patients relative to the controls. Using FC, we found the abnormal GM regions did not display abnormal functional connectivity. Lastly, we found in left TLE patients, verbal episodic memory was associated with abnormal left posterior hippocampus volume, while in right TLE, non-verbal episodic memory was better predicted by resting-state FC measures. This study investigated TLE abnormalities using a multi-modal approach combining GM, FC and neurocognitive measures. We did not find that the GM abnormalities were functionally or abnormally connected during an inter-ictal resting state, which may reflect a weak sensitivity of functional connectivity to the epileptic network. We provided evidence that verbal and non-verbal episodic memory in left and right TLE patients may have distinct relationships with structural and functional measures. Lastly, we provide data suggesting that in the setting of occult, non-lesional right TLE pathology, a coupling of structural and functional abnormalities in extra-temporal/non-ictal regions is necessary to produce reductions in episodic memory recall. The latter, in particular, demonstrates the complex structure/function interactions at work when trying to understand cognition in TLE, suggesting that subtle network effects can emerge bearing specific relationships to hemisphere and the type of pathology.

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

OBJECTIVE

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

RESULTS

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

CONCLUSIONS

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

Frontal gray matter abnormalities predict seizure outcome in refractory temporal lobe epilepsy patients

Developing more reliable predictors of seizure outcome following temporal lobe surgery for intractable epilepsy is an important clinical goal. In this context, we investigated patients with refractory temporal lobe epilepsy (TLE) before and after temporal resection. In detail, we explored gray matter (GM) volume change in relation with seizure outcome, using a voxel-based morphometry (VBM) approach. To do so, this study was divided into two parts. The first one involved group analysis of differences in regional GM volume between the groups (good outcome (GO), e.g., no seizures after surgery; poor outcome (PO), e.g., persistent postoperative seizures; and controls, N = 24 in each group), pre- and post-surgery. The second part of the study focused on pre-surgical data only (N = 61), determining whether the degree of GM abnormalities can predict surgical outcomes. For this second step, GM abnormalities were identified, within each lobe, in each patient when compared with an ad hoc sample of age-matched controls. For the first analysis, the results showed larger GM atrophy, mostly in the frontal lobe, in PO patients, relative to both GO patients and controls, pre-surgery. When comparing pre-to-post changes, we found relative GM gains in the GO but not in the PO patients, mostly in the non-resected hemisphere. For the second analysis, only the frontal lobe displayed reliable prediction of seizure outcome. 81% of the patients showing pre-surgical increased GM volume in the frontal lobe became seizure free, post-surgery; while 77% of the patients with pre-surgical reduced frontal GM volume had refractory seizures, post-surgery. A regression analysis revealed that the proportion of voxels with reduced frontal GM volume was a significant predictor of seizure outcome (p = 0.014). Importantly, having less than 1% of the frontal voxels with GM atrophy increased the likelihood of being seizure-free, post-surgery, by seven times. Overall, our results suggest that using pre-surgical GM abnormalities within the frontal lobe is a reliable predictor of seizure outcome post-surgery in TLE. We believe that this frontal GM atrophy captures seizure burden outside the pre-existing ictal temporal lobe, reflecting either the development of epileptogenesis or the loss of a protective, adaptive force helping to control or limit seizures. This study provides evidence of the potential of VBM-based approaches to predict surgical outcomes in refractory TLE candidates.

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Gray matter abnormalities within the frontal lobe predicts seizure outcome in TLE.

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Poor outcome patients suffer from GM atrophy in the frontal lobe, pre-surgery.

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Good outcome patients show gain of GM in the non-resected hemisphere, post-surgery.

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Frontal GM atrophy captures seizure burden outside the ictal temporal lobe.

Reduced thalamocortical functional connectivity in temporal lobe epilepsy

OBJECTIVE

In temporal lobe epilepsy (TLE), the thalamus is well known for its role in the propagation and spread of epileptiform activity. However, the integrity of thalamocortical functional connectivity (FC) in TLE and its relation to specific seizure patterns have not yet been determined. We address these issues with resting-state functional magnetic resonance imaging (fMRI).

METHODS

Resting-state fMRI was performed on two groups of unilateral TLE patients: those with focal seizures only (16 left TLE, 16 right TLE) and those with additional generalized seizures (16 left TLE, 10 right TLE), and 16 matched controls. A thalamic parcellation based on FC between five nonoverlapping cortical seeds (prefrontal, motor, somatosensory, parietal-occipital, and temporal) and the ipsilateral thalamus was carried out to parcel each thalamus into five corresponding segments. FCs between each segment and its ipsilateral cortical seed were extracted and compared across groups using analyses of variance (ANOVAs).

RESULTS

Compared to healthy controls, patients with TLE displayed decreased thalamocortical FC in multiple posterior and ventromedial thalamic segments of both the ictal and nonictal hemispheres. Our parcellation analysis revealed that these thalamic regions were functionally connected to the parietal/occipital and temporal lobes. In patients with TLE with focal seizures these regional thalamocortical FC decreases were limited to the ictal hemisphere. In contrast, TLE patients with both focal and generalized epileptiform activity displayed FC decreases in both the ictal and nonictal thalamus involving the dorsolateral pulvinar, a region preferentially connected to the parietal and occipital lobes.

SIGNIFICANCE

Our data provide the first evidence of regional specific thalamocortical FC decreases in patients with unilateral TLE. Furthermore, our results demonstrate that patients with different seizure types present different thalamoparietal/occipital FC decrease patterns. While patients with focal seizures present thalamocortical FC decreases in the ictal hemisphere only, patients with additional generalized seizure activity also show thalamocortical FC decreases involving the thalamus in the nonictal hemisphere.

Presurgery resting-state local graph-theory measures predict neurocognitive outcomes after brain surgery in temporal lobe epilepsy

OBJECTIVE

This study determined the ability of resting-state functional connectivity (rsFC) graph-theory measures to predict neurocognitive status postsurgery in patients with temporal lobe epilepsy (TLE) who underwent anterior temporal lobectomy (ATL).

METHODS

A presurgical resting-state functional magnetic resonance imaging (fMRI) condition was collected in 16 left and 16 right TLE patients who underwent ATL. In addition, patients received neuropsychological testing pre- and postsurgery in verbal and nonverbal episodic memory, language, working memory, and attention domains. Regarding the functional data, we investigated three graph-theory properties (local efficiency, distance, and participation), measuring segregation, integration and centrality, respectively. These measures were only computed in regions of functional relevance to the ictal pathology, or the cognitive domain. Linear regression analyses were computed to predict the change in each neurocognitive domain.

RESULTS

Our analyses revealed that cognitive outcome was successfully predicted with at least 68% of the variance explained in each model, for both TLE groups. The only model not significantly predictive involved nonverbal episodic memory outcome in right TLE. Measures involving the healthy hippocampus were the most common among the predictors, suggesting that enhanced integration of this structure with the rest of the brain may improve cognitive outcomes. Regardless of TLE group, left inferior frontal regions were the best predictors of language outcome. Working memory outcome was predicted mostly by right-sided regions, in both groups. Overall, the results indicated our integration measure was the most predictive of neurocognitive outcome. In contrast, our segregation measure was the least predictive.

SIGNIFICANCE

This study provides evidence that presurgery rsFC measures may help determine neurocognitive outcomes following ATL. The results have implications for refining our understanding of compensatory reorganization and predicting cognitive outcome after ATL. The results are encouraging with regard to the clinical relevance of using graph-theory measures in presurgical algorithms in the setting of TLE.

Resting-state functional connectivity predicts the strength of hemispheric lateralization for language processing in temporal lobe epilepsy and normals

In temporal lobe epilepsy (TLE), determining the hemispheric specialization for language before surgery is critical to preserving a patient's cognitive abilities post-surgery. To date, the major techniques utilized are limited by the capacity of patients to efficiently realize the task. We determined whether resting-state functional connectivity (rsFC) is a reliable predictor of language hemispheric dominance in right and left TLE patients, relative to controls. We chose three subregions of the inferior frontal cortex (pars orbitalis, pars triangularis, and pars opercularis) as the seed regions. All participants performed both a verb generation task and a resting-state fMRI procedure. Based on the language task, we computed a laterality index (LI) for the resulting network. This revealed that 96% of the participants were left-hemisphere dominant, although there remained a large degree of variability in the strength of left lateralization. We tested whether LI correlated with rsFC values emerging from each seed. We revealed a set of regions that was specific to each group. Unique correlations involving the epileptic mesial temporal lobe were revealed for the right and left TLE patients, but not for the controls. Importantly, for both TLE groups, the rsFC emerging from a contralateral seed was the most predictive of LI. Overall, our data depict the broad patterns of rsFC that support strong versus weak left hemisphere language laterality. This project provides the first evidence that rsFC data may potentially be used on its own to verify the strength of hemispheric dominance for language in impaired or pathologic populations.

Hippocampal functional connectivity patterns during spatial working memory differ in right versus left temporal lobe epilepsy

Temporal lobe epilepsy (TLE), affecting the medial temporal lobe, is a disorder that affects not just episodic memory but also working memory (WM). However, the exact nature of hippocampal-related network activity in visuospatial WM remains unclear. To clarify this, we utilized a functional connectivity (FC) methodology to investigate hippocampal network involvement during the encoding phase of a functional magnetic resonance imaging (fMRI) visuospatial WM task in right and left TLE patients. Specifically, we assessed the relation between FC within right and left hippocampus-seeded networks, and patient performance (rate of correct responses) during the encoding phase of a block span WM task. Results revealed that both TLE groups displayed a negative relation between WM performance and FC between the left hippocampus and ipsilateral parahippocampal gyrus. We also found a positive relationship between performance and FC between the left hippocampus seed and the precuneus, in the right TLE group. Lastly, the left TLE specifically demonstrated a negative relationship between performance and FC between both hippocampi and ipsilateral cerebellar clusters. Our findings indicate that right and left TLE groups may develop different patterns of FC to implement visuospatial WM. Indeed, the present result suggests that FC provides a unique means of identifying abnormalities in brain networks, which cannot be discerned at the level of behavioral output through neuropsychological testing. More broadly, our findings demonstrate that FC methods applied to task-based fMRI provide the opportunity to define specific task-related networks.

Temporal lobe epilepsy and surgery selectively alter the dorsal, not the ventral, default-mode network

The default-mode network (DMN) is a major resting-state network. It can be divided in two distinct networks: one is composed of dorsal and anterior regions [referred to as the dorsal DMN (dDMN)], while the other involves the more posterior regions [referred to as the ventral DMN (vDMN)]. To date, no studies have investigated the potentially distinct impact of temporal lobe epilepsy (TLE) on these networks. In this context, we explored the effect of TLE and anterior temporal lobectomy (ATL) on the dDMN and vDMN. We utilized two resting-state fMRI sessions from left, right TLE patients (pre-/post-surgery) and normal controls (sessions 1/2). Using independent component analysis, we identified the two networks. We then evaluated for differences in spatial extent for each network between the groups, and across the scanning sessions. The results revealed that, pre-surgery, the dDMN showed larger differences between the three groups than the vDMN, and more particularly between right and left TLE than between the TLE patients and controls. In terms of change post-surgery, in both TLE groups, the dDMN also demonstrated larger changes than the vDMN. For the vDMN, the only changes involved the resected temporal lobe for each ATL group. For the dDMN, the left ATL group showed post-surgical increases in several regions outside the ictal temporal lobe. In contrast, the right ATL group displayed a large reduction in the frontal cortex. The results highlight that the two DMNs are not impacted by TLE and ATL in an equivalent fashion. Importantly, the dDMN was the more affected, with right ATL having a more deleterious effects than left ATL. We are the first to highlight that the dDMN more strongly bears the negative impact of TLE than the vDMN, suggesting there is an interaction between the side of pathology and DM sub-network activity. Our findings have implications for understanding the impact TLE and subsequent ATL on the functions implemented by the distinct DMNs.

Functional connectivity abnormalities vary by amygdala subdivision and are associated with psychiatric symptoms in unilateral temporal epilepsy

The amygdala has been described as a structure affected by mesial temporal lobe epilepsy (MTLE). Indeed, it is suggested that amygdala abnormalities are related to the co-morbid depression and anxiety reported in MTLE. In this context, we investigated the relation between functional connectivity (FC) emerging from this structure in fMRI and depression and anxiety levels reported in MTLE patients. We focused on resting-state BOLD activity and evaluated whether FC differences emerge from each of three amygdala subdivisions (laterobasal, centromedial and superficial) in left and right MTLE groups, compared with healthy controls. Results revealed significant differences between patient groups and controls. Specifically, the left MTLE group showed abnormal FC for the left-sided seeds only. Furthermore, regardless of the seed, we observed more reliable differences between the right MTLE group and controls. Further analysis of these results revealed correlations between these impaired connectivities and psychiatric symptoms in both MTLE groups. Opposite relations, however, were highlighted: the more depressed or anxious the right MTLE patients, the closer their FC values approached controls; whereas the less anxious the left MTLE patients, the closer their FC values were normative. These results highlight how MTLE alter FC emerging from the limbic system. Overall, our data demonstrate that right TLE has a more maladaptive impact on emotion-related networks, in ways specific to the amygdala region, and the emotion symptom involved, than left TLE.

An investigation of implicit memory through left temporal lobectomy for epilepsy

Temporal lobe epilepsy patients have demonstrated a relative preservation in the integrity of implicit memory procedures. We examined performance in a verbal implicit and explicit memory task in left anterior temporal lobectomy patients (LATL) and healthy normal controls (NCs) while undergoing fMRI. We hypothesized that despite the relative integrity of implicit memory in both the LATL patients and normal controls, the two groups would show distinct functional neuroanatomic profiles during implicit memory. LATLs and NCs performed Jacoby's Process Dissociation Process (PDP) procedure during fMRI, requiring completion of word stems based on the previously studied words or new/unseen words. Measures of automaticity and recollection provided uncontaminated indices of implicit and explicit memory, respectively. The behavioral data showed that in the face of temporal lobe pathology implicit memory can be carried out, suggesting implicit verbal memory retrieval is non-mesial temporal in nature. Compared to NCs, the LATL patients showed reliable activation, not deactivation, during implicit (automatic) responding. The regions mediating this response were cortical (left medial frontal and precuneus) and striatal. The active regions in LATL patients have the capacity to implement associative, conditioned responses that might otherwise be carried out by a healthy temporal lobe, suggesting this represented a compensatory activity. Because the precuneus has also been implicated in explicit memory, the data suggests this structure may have a highly flexible functionality, capable of supporting implementation of either explicit memory, or automatic processes such as implicit memory retrieval. Our data suggest that a healthy mesial/anterior temporal lobe may be needed for generating the posterior deactivation perceptual priming response seen in normals.

Functional connectivity evidence of cortico-cortico inhibition in temporal lobe epilepsy

Epileptic seizures can initiate a neural circuit and lead to aberrant neural communication with brain areas outside the epileptogenic region. We focus on interictal activity in focal temporal lobe epilepsy and evaluate functional connectivity (FC) differences that emerge as function of bilateral versus strictly unilateral epileptiform activity. We assess the strength of FC at rest between the ictal and non-ictal temporal lobes, in addition to whole brain connectivity with the ictal temporal lobe. Results revealed strong connectivity between the temporal lobes for both patient groups, but this did not vary as a function of unilateral versus bilateral interictal status. Both the left and right unilateral temporal lobe groups showed significant anti-correlated activity in regions outside the epileptogenic temporal lobe, primarily involving the contralateral (non-ictal/non-pathologic) hemisphere, with precuneus involvement prominent. The bilateral groups did not show this contralateral anti-correlated activity. This anti-correlated connectivity may represent a form of protective and adaptive inhibition, helping to constrain epileptiform activity to the pathologic temporal lobe. The absence of this activity in the bilateral groups may be indicative of flawed inhibitory mechanisms, helping to explain their more widespread epileptiform activity. Our data suggest that the location and build up of epilepsy networks in the brain are not truly random, and are not limited to the formation of strictly epileptogenic networks. Functional networks may develop to take advantage of the regulatory function of structures such as the precuneus to instantiate an anti-correlated network, generating protective cortico-cortico inhibition for the purpose of limiting seizure spread or epileptogenesis.

A conceptual framework for interpreting neuroimaging studies of brain neuroplasticity and cognitive recovery

Functional neuroimaging technologies are increasingly being used to predict cognitive/behavioral outcomes after the initiation of clinical interventions such as resective surgery or cognitive rehabilitation. We provide a conceptual model and a case example to explain how the results from various neuroimaging techniques can be integrated to answer important questions about clinical recovery such as whether neural reorganization has occurred and, if so, the type of adaptive cognitive mechanism driving this reorganization. This proposed framework and its use in interpreting neuroimaging outcomes studies should help uncover the principles that govern neural reorganization, and be of use to any patient for whom the risk, or potential benefit, of brain-based interventions is unknown.

Extratemporal functional connectivity impairments at rest are related to memory performance in mesial temporal epilepsy

Mesial temporal lobe epilepsy (MTLE) is the most frequent form of focal epilepsy. At rest, there is evidence that brain abnormalities in MTLE are not limited to the epileptogenic region, but extend throughout the whole brain. It is also well established that MTLE patients suffer from episodic memory deficits. Thus, we investigated the relation between the functional connectivity seen at rest in fMRI and episodic memory impairments in MTLE. We focused on resting state BOLD activity and evaluated whether functional connectivity (FC) differences emerge from MTL seeds in left and right MTLE groups, compared with healthy controls. Results revealed significant FC reductions in both patient groups, localized in angular gyri, thalami, posterior cingulum and medial frontal cortex. We found that the FC between the left non-pathologic MTL and the medial frontal cortex was positively correlated with the delayed recall score of a non-verbal memory test in right MTLE patients, suggesting potential adaptive changes to preserve this memory function. In contrast, we observed a negative correlation between a verbal memory test and the FC between the left pathologic MTL and posterior cingulum in left MTLE patients, suggesting potential functional maladaptative changes in the pathologic hemisphere. Overall, the present study provides some indication that left MTLE may be more impairing than right MTLE patients to normative functional connectivity. Our data also indicates that the pattern of extra-temporal FC may vary as a function of episodic memory material and each hemisphere's capacity for cognitive reorganization.

Employment after anterior temporal lobectomy

PURPOSE

To explore the effect of anterior temporal lobectomy on employment and define demographic and clinical predictors of postoperative employment in a large cohort with a prolonged observational period.

METHODS

Subjects had an anterior temporal lobectomy for refractory epilepsy. All had an assessment period of 4 years or more with documentation of demographic factors, employment status, and seizure frequency prospectively registered in a database at surgery and at each contact after surgery. McNemar chi-square and a Wilcoxon matched pairs test were used to compare employment status before and after surgery. A multiple logistic regression assessed independent predictors of postoperative employment status based on preoperative employment status.

KEY FINDINGS

Three hundred sixty-nine patients were evaluated. Employment levels were higher and unemployment levels were lower after surgery (McNemar χ(2) = 3.96; p = 0.047). Working before surgery (Wald's χ(2) = 22.69, p < 0.0001) and having a greater percent of seizure-free years (Wald's χ(2) = 34.43, p < 0.0001) were associated with being employed after surgery. Of 131 patients who were unemployed or homemakers before surgery, 67 (51.1%) became employed postoperatively, with a younger age at surgery, a younger age of epilepsy onset, and driving a motor vehicle associated with gaining employment. Of 172 patients who were working at baseline, 27 (15.7%) became unemployed or homemakers after surgery. Gender was the only variable associated with loss of employment, with women being more likely to become homemakers (χ(2) = 14.98, d.f.= 6, p = 0.02). Most students were working after surgery, with seizure control influencing outcome.

SIGNIFICANCE

Anterior temporal lobectomy is followed by reduced unemployment and underemployment, with elimination of seizures, relative youth, and operating a motor vehicle serving as the main driving forces for improvement. This is important information for patients and physicians who contemplate surgery as it helps define reasonable expectations, and provides further objective evidence for benefits beyond purely medical outcomes after epilepsy surgery.

Hippocampal volumetry and functional MRI of memory in temporal lobe epilepsy

This study examined the utility of structural and functional MRI at 1.5 and 3T in the presurgical evaluation and prediction of postsurgical cognitive outcome in temporal lobe epilepsy (TLE). Forty-nine patients undergoing presurgical evaluation for temporal lobe (TL) resection and 25 control subjects were studied. Patients completed standard presurgical evaluations, including the intracarotid amobarbital test (IAT) and neuropsychological testing. During functional imaging, subjects performed a complex visual scene-encoding task. High-resolution structural MRI scans were used to quantify hippocampal volumes. Both structural and functional imaging successfully lateralized the seizure focus and correlated with IAT memory lateralization, with improvement for functional imaging at 3T as compared with 1.5 T. Ipsilateral structural and functional MRI data were related to cognitive outcome, and greater functional asymmetry was related to earlier age at onset. These findings support continued investigation of the utility of MRI and fMRI in the presurgical evaluation of TLE.

Assessing the relationship between craving and relapse

The value of craving as a construct in the substance use disorders literature stems from its purported ability to predict actual alcohol or psychoactive drug consumption. Empirical reports of craving's relationship to actual use, however, are quite mixed. It is argued that craving's relationship to use variables such as relapse will remain unclear until individual differences related to acting on craving are considered. Such potential mediators of craving's relationship to relapse, such as impulsivity, are evaluated. The implications of this argument for the construct of craving are discussed.

Health locus of control in patients with epilepsy and its relationship to anxiety, depression, and seizure control

OBJECTIVE

A person's health locus of control orientation is one of several factors that determine which health-related behaviors a person will perform. The aim of this study was to determine the health locus of control in patients with epilepsy and its relationship to anxiety, depression, and seizure control.

METHODS

Adults aged 18 and older who had had epilepsy for at least 1 year were recruited in either the inpatient epilepsy monitoring unit or the outpatient epilepsy clinic at Thomas Jefferson University in 2006. Patients anonymously filled out a questionnaire, which elicited data on age, sex, education, and seizure control. The Hospital Anxiety and Depression (HAD) scale was used to evaluate anxiety level and depression, and Form C of the Multidimensional Health Locus of Control (MHLC) scales was used to evaluate the health locus of control. Statistical analyses were performed using regression analyses to determine potentially significant associations.

RESULTS

Two hundred patients with a mean age of 40.3 +/- 16 participated. Patients had low mean scores on the Internal, medium mean scores on the Chance, and high mean scores on the Powerful Others MHLC subscales. Patients with epilepsy with higher Internal MHLC scores more frequently had controlled seizures. Patients with higher Powerful Others MHLC scores had higher scores on the Anxiety subscale of the HAD scale.

CONCLUSIONS

Patients with epilepsy in our study had weak perceptions of internal and strong perceptions of external health locus of control. This probably means patients with epilepsy might adapt less effectively to their illness and have lower levels of engagement in beneficial health behaviors and active coping strategies.

The effectiveness of low-frequency stimulation for mapping cortical function

OBJECTIVE

To establish the efficacy and safety of low-frequency electrical stimulation for cortical brain mapping.

METHODS

Cortical function was mapped using electrical stimulation in epilepsy patients with chronically implanted intracranial subdural electrodes. Contacts overlying motor, sensory, visual, and language cortex were stimulated at frequencies of 5, 10, and 50 Hz, using current levels ranging from 1 to 17.5 mA for 3-5 s. The current intensity and incidence at which functional alterations and afterdischarges (ADs) occurred were recorded. The modified McNemar test for nonindependent measures was used to analyze the data.

RESULTS

122 electrode contact pairs were electrically stimulated at least two different frequencies in 14 patients. Functional alterations were obtained at all stimulation frequencies (5, 10, and 50 Hz) at generally similar rates. The likelihood of producing an AD correlated with stimulation frequency, and lower-frequency stimulation was less likely to provoke an AD. Higher current intensity was required to induce both functional responses and ADs at low-frequency stimulation than high-frequency stimulation. While overall rates of producing functional changes were similar, differences in functional response with regard to frequency were noted at individual cortical sites.

CONCLUSION

5- and 10-Hz stimulation are as effective for mapping cortical function as 50-Hz stimulation and produce fewer ADs. We recommend that mapping of cortical function be started with 5-Hz-frequency stimulation. Higher frequencies should be used in suspect cortex if no symptoms or signs are produced with 5-Hz stimulation.

Are depression and cognitive performance related in temporal lobe epilepsy?

PURPOSE

The degree to which depression interacts with the cognitive deficits of epilepsy to alter cognitive skill and general functioning is unknown. Depression has significant negative effects on adaptive functioning including cognitive skills. Temporal lobe epilepsy (TLE) patients are known to possess cognitive dysfunction. Thus, TLE patients who are depressed may suffer a double burden of cognitive deficits.

METHODS

We examined whether depressed patients show increased cognitive deficits relative to nondepressed TLE patients (n = 59). We then sought to determine if this effect varied for left versus right TLE patients utilizing preoperative depression and neuropsychological data. To accurately study the lateralization of any observed effects, we selected only patients with definitive evidence of unilateral pathology and seizure focus and utilized a two-year seizure-free postsurgical outcome to capture this.

RESULTS

The data suggested that cognitive performance was not related to depression, and that depression did not reliably mediate the cognitive presentation of either our left or right TL patients. The notion of a double burden on cognition did not receive support from our data. The data did produce the expected advantage on verbal memory measures for right TLE patients.

CONCLUSIONS

The reasons for the limited statistical effects are discussed and issues in unraveling the causal relationships between depression, cognition, and TLE are considered. We discussed the potential role depression may play in the cognitive skills of TLE patients, but the major implication is that depression and neurocognitive performance appear to bear a limited relationship in the context of TLE.

A Bayesian approach for the categorization of radiology reports

RATIONALE AND OBJECTIVE

We sought to develop a Bayesian-filter that could distinguish positive radiology computed tomography (CT) reports of appendicitis from negative reports with no appendicitis.

MATERIALS AND METHODS

Standard unstructured electronic text radiology reports containing the key word appendicitis were obtained using a Java-based text search engine from a hospital General Electric PACS system. A total of 500 randomly selected reports from multiple radiologists were then manually categorized and merged into two separate text files: 250 positive reports and 250 negative findings of appendicitis. The two text files were then processed by the freely available UNIX-based software dbacl 1.9, a digramic Bayesian classifier for text recognition, on a Linux based Pentium 4 system. The software was then trained on the two separate merged text files categories of positive and negative appendicitis. The ability of the Bayesian filter to discriminate between reports of negative and positive appendicitis images was then tested on 100 randomly selected reports of appendicitis: 50 positive cases and 50 negative cases.

RESULTS

The training time for the Bayesian filter was approximately 2 seconds. The Bayesian filter subsequently was able to categorize 50 of 50 positive reports of appendicitis and 50 of 50 reports of negative appendicitis, in less than 10 seconds.

CONCLUSION

A Bayesian-filter system can be used to quickly categorize radiology report findings and automatically determine after training, with a high degree of accuracy, whether the reports have text findings of a specific diagnosis. The Bayesian filter can potentially be applied to any type of radiologic report finding and any relevant category.

Evaluation of neurologic deficit without apparent cause: the importance of a multidisciplinary approach

BACKGROUND/OBJECTIVE

A patient presenting with an acute neurologic deficit with no apparent etiology presents a diagnostic dilemma. A broad differential diagnosis must be entertained, considering both organic and psychiatric causes.

METHODS

A case report and thorough literature review of acute paraplegia after a low-energy trauma without a discernible organic etiology.

RESULTS

Diagnostic imaging excluded any bony malalignment or fracture and any abnormality on magnetic resonance imaging. When no organic etiology was identified, a multidisciplinary approach using neurology, psychiatry, and physical medicine and rehabilitation services was applied. Neurophysiologic testing confirmed the absence of an organic disorder, and at this juncture, diagnostic efforts focused on identifying any psychiatric disorder to facilitate appropriate treatment for this individual. The final diagnosis was malingering.

CONCLUSIONS

The full psychiatric differential diagnosis should be considered in the evaluation of any patient with an atypical presentation of paralysis. A thorough clinical examination in combination with the appropriate diagnostic studies can confidently exclude an organic disorder. When considering a psychiatric disorder, the differential diagnosis should include conversion disorder and malingering, although each must remain a diagnosis of exclusion. Maintaining a broad differential diagnosis and involving multiple disciplines (neurology, psychiatry, social work, medical specialists) early in the evaluation of atypical paralysis may facilitate earlier diagnosis and initiation of treatment for the underlying etiology.

Corpus callosotomy in refractory idiopathic generalized epilepsy

RATIONALE

A small percentage of patients with idiopathic generalized epilepsy (IGE) do not respond to medical therapy. Generalized tonic-clonic (GTC) seizures are especially debilitating and can be associated with severe injuries. The benefit, safety and effect of corpus callosotomy (CC) in patients with IGE have not been studied.

METHODS

We reviewed patients with presumed IGE who underwent CC between 1991 and 2000. Criteria for selection included history, examination, brain imagining, interictal and ictal EEG. All patients had refractory and debilitating tonic-clonic seizures (GTCS) and had failed four or more antiepileptic drugs. Seizure frequency was calculated per month over the last year and pre-operative baseline was compared to last follow-up using paired t-tests. IQ, executive function, language and verbal, non-verbal memory and quality of life (QOL) was compared before and after surgery. Serial EEGs after surgery were reviewed.

RESULTS

There were nine patients (seven men), mean age 37.9 (range: 22-49), mean IQ 87.3 (range: 75-107). All had anterior CC. Mean follow-up time was 5.4 years (range: 0.6-10.3 years). One patient died from sudden death in epilepsy 9 months after surgery. There was a significant reduction of GTC seizures from 6.3 to 1.1 (p<0.005). Four patients had more than 80% and eight more than 50% reduction. Of five patients with absence seizures, two became seizure free and one had more than 80% reduction and two worsened slightly, and of three with myoclonic seizures one had more than 90% reduction. One patient had completion of the CC with improvement of myoclonus and absence seizures, but not of GTC seizures and suffered a disconnection syndrome. Another had right frontal focal resection without improvement after new seizures of focal onset. Cognitive testing showed a good outcome (improved or no change) in all cognitive domains. Post-surgical EEG showed new focal slowing and sharp waves. There was no change in QOL.

CONCLUSION

CC can be effective in reducing GTC, absence and myoclonic seizures in patients with refractory IGE. These findings suggest that interhemispheric communication of the cerebral cortices plays an important role in the generation of seizures in IGE. Anterior CC appears safe while complete callosotomy has a risk of disconnection syndrome.

Subjective somnolence relates mainly to depression among patients in a tertiary care epilepsy center

Many patients with epilepsy complain of decreased energy and somnolence. There is increased awareness that comorbidity, especially depression, plays an important role in determining the quality of life for patients with epilepsy. We set out to determine how subjective somnolence is affected by depression, age, hours of sleep, sleep apnea, seizure frequency, and numbers of antiepileptic drugs and central nervous system drugs. A questionnaire and chart review were used to investigate patients in a tertiary referral center. We found that subjective somnolence was prominent and that it relates mainly to depression, less to obstructive sleep apnea, and not to the other variables. Further investigation is needed into the relationship between depression and subjective somnolence in patients with epilepsy.

The association of mood with quality of life ratings in epilepsy

OBJECTIVE

To determine the relative contributions of psychological (mood and anxiety), social, and seizure-related variables to quality of life (QOL) scores in epilepsy.

METHODS

Outpatients (n = 435) with epilepsy completed the Quality of Life in Epilepsy 31 Inventory (QOLIE-31), Beck Depression Inventory II (BDI-II), Beck Anxiety Inventory, and a social survey. Stepwise linear regression and general linear model analyses determined the set of best predictors and the most unique predictors of composite QOLIE-31 score and subscale scores.

RESULTS

A three-variable model accounted for 56% of the variance for the composite QOLIE-31 score. The BDI-II was the strongest (often by several multiples in terms of variance explained) and most consistent predictor of the composite and QOLIE subscales in both types of analytic approaches. In no case did BDI-II significantly interact with the other variables, suggesting that its effect on QOL was direct and not mediated by other factors. Throughout the results, depression had an inverse relation to scores, i.e., lower levels of depression correlated with high QOL scores. Separate correlational analyses showed that poor seizure control was associated with increased numbers of depressive symptoms.

DISCUSSION

Quality of Life in Epilepsy (QOLIE) scores, reflecting both general and specific aspects of quality of life, are strongly influenced by mood state, such as depression. Factors such as seizure control exert a more limited effect on the QOLIE. Health-related quality of life measures are needed in which mood does not play such a dominant role.

Predicting seizure frequency after epilepsy surgery

OBJECTIVE

To identify clinical features related to seizure frequency after epilepsy surgery in patients with recurrent seizures.

BACKGROUND

No studies have examined the differences between patients who have rare seizures and patients who experience frequent seizures after epilepsy surgery. Since seizure frequency correlates with morbidity and quality of life, it is desirable to know which preoperative clinical features predict postoperative seizure frequency.

METHODS

Patients with recurrent seizures were placed in two categories: rare postoperative seizures (< or =2 per year) and frequent postoperative seizures (> or =12 per year) using seizure frequency in the second postoperative year. Variables included preoperative seizure frequency, age of first risk, age at first seizure, epilepsy duration, age at surgery, history of febrile convulsions, tonic-clonic seizures, status epilepticus, or family history, IQ, magnetic resonance imaging (MRI), and positron emission tomography (PET). Variables were analyzed using non-parametric tests to assess relationship to postoperative seizure frequency.

RESULTS

Of 475 patients who had epilepsy surgery, 111 had rare or frequent seizures in the second postoperative year. After anterior temporal lobectomy (ATL), age of first risk< or =5 years and presence of mesial temporal sclerosis on MRI were associated with rare seizures (66% of patients), whereas lack of these risk factors was associated with frequent seizures (75% of patients) (p<0.03). For non-ATL operations, preoperative seizure frequency of > or =20 seizures per month was associated with frequent postoperative seizures (p=0.03). No other variables influenced outcome.

CONCLUSIONS

Some preoperative clinical features correlate with postoperative seizure frequency in patients with recurrent seizures after epilepsy surgery. This has implications for the surgical decision making process and early postoperative management.

Functional MRI predicts post-surgical memory following temporal lobectomy

Temporal lobectomy is an effective therapy for medically refractory temporal lobe epilepsy (TLE), but may be complicated by amnestic syndromes. Therefore, pre-surgical evaluation to assess the risk/benefit ratio for surgery is required. Intracarotid amobarbital testing (IAT) is currently the most widely used method for assessing pre-surgical memory lateralization, but is relatively invasive. Over the past decade functional MRI (fMRI) has been shown to correlate with IAT for language lateralization, and also for memory lateralization in a small number of patients. This study was carried out to compare fMRI during memory encoding with IAT testing for memory lateralization, and to assess the predictive value of fMRI during memory encoding for post-surgical memory outcome. Thirty-five patients with refractory TLE undergoing pre-surgical evaluation for temporal lobectomy and 30 normal subjects performed a complex visual scene-encoding task during fMRI scanning at 1.5 T using a 10-min protocol. Encoding performance was evaluated with subsequent recognition testing. Twenty-three patients also completed the same task again outside the scanner, an average of 6.9 months following surgery. A region of interest (ROI) analysis was used to quantify activation within hippocampal and a larger mesial temporal lobe ROI consisting of hippocampus, parahippocampus and fusiform gyrus (HPF) as defined by a published template. Normal subjects showed almost symmetrical activation within these ROI. TLE patients showed greater asymmetry. Asymmetry ratios (ARs) from the HPF ROI correlated significantly with memory lateralization by intracarotid amobarbital testing. HPF ARs also correlated significantly with memory outcome, as determined by a change in scene recognition between pre-surgical and post-surgical trials. When absolute activation within the HPF ROI was considered, a significant inverse correlation between activation ipsilateral to temporal lobectomy and memory outcome was observed, with no significant correlation in the contralateral HPF ROI. Although further technical improvements and prospective clinical validation are required, these results suggest that mesial temporal memory activation detected by fMRI during complex visual scene encoding correlates with post-surgical memory outcome and supports the notion that this approach will ultimately contribute to patient management.

Differential brain responses when applying criterion attribute versus family resemblance rule learning

Subsystems of category learning have been identified on the basis of general domains of content (e.g., tools, faces). The present study examined categories from the standpoint of internal structure and determined brain topography associated with expressing two fundamentally different category rule structures (criterion attribute, CA, and family resemblance, FR). CA category learning involves processing stimuli by isolated features and classifying by properties held by all members. FR learning involves processing stimuli by integral wholes and classifying on overall similarity among members without sharing identical features. fMRI BOLD response to CA and FR categorization was measured with pseudowords as stimuli. Category knowledge for both tasks was mastered prior to brain imaging. Areas of activation emerged unique to the structure of each category and followed from the nature of the rule abstraction procedure. CA categorization was implemented by strong target monitoring and expectation (medial parietal), rule maintenance in working memory, feature selection processes (inferior frontal), and a sensitivity to high frequency components of the stimulus such as isolated features (anterior temporal). FR categorization, consistent with its multi-featural nature, involved word-level processing (left extrastriate) that evoked articulatory rehearsal (medial cerebellar). The data suggest category structure is an important determinant of brain response during categorization. For instance, anterior temporal structures may help attune visual processing systems to high frequency components to support the learning of criterial, highly predictive rules.