Atypical language representation in epilepsy: implications for injury-induced reorganization of brain function

Seizure, Motor, and Cognitive Outcomes After Epilepsy Surgery for Patients With Sturge-Weber Syndrome: Results From a Multicenter Study

BACKGROUND AND OBJECTIVES

Surgery is widely performed for refractory epilepsy in patients with Sturge-Weber syndrome (SWS), but reports on its effectiveness are limited. This study aimed to analyze seizure, motor, and cognitive outcomes of surgery in these patients and to identify factors associated with the outcomes.

METHODS

This was a multicenter retrospective observational study using data from patients with SWS and refractory epilepsy who underwent epilepsy surgery between 2000 and 2020 at 16 centers throughout China. Longitudinal postoperative seizures were classified by Engel class, and Engel class I was regarded as seizure-free outcome. Functional (motor and cognitive) outcomes were evaluated using the SWS neurologic score, and improved or unchanged scores between baseline and follow-up were considered to have stable outcomes. Outcomes were analyzed using Kaplan-Meier analyses. Multivariate Cox regression was used to identify factors associated with outcomes.

RESULTS

A total of 214 patients with a median age of 2.0 (interquartile range 1.2-4.6) years underwent surgery (focal resection, FR [n = 87]; hemisphere surgery, HS [n = 127]) and completed a median of 3.5 (1.7-5.0) years of follow-up. The overall estimated probability for being seizure-free postoperatively at 1, 2, and 5 years was 86.9% (95% CI 82.5-91.6), 81.4% (95% CI 76.1-87.1), and 70.7% (95% CI 63.3-79.0), respectively. The overall estimated probability of being motor stable at the same time post operatively was 65.4% (95% CI 58.4-71.2), 80.2% (95% CI 73.8-85.0), and 85.7% (95% CI 79.5-90.1), respectively. The overall probability for being cognition stable at 1, 2, and 5 years was 80.8% (95% CI 74.8-85.5), 85.1% (95% CI 79.3-89.2), and 89.5% (95% CI 83.8-93.2), respectively. Both FR and HS were effective at ensuring seizure control. For different HS techniques, modified hemispherotomy had comparable outcomes but improved safety compared with anatomical hemispherectomy. Regarding FR, partial resection (adjusted hazard ratio [aHR] 11.50, 95% CI 4.44-29.76), acute postoperative seizure (APOS, within 30 days of surgery; aHR 10.33, 95% CI 3.94-27.12), and generalized seizure (aHR 3.09, 95% CI 1.37-6.94) were associated with seizure persistence. For HS, seizure persistence was associated with APOS (aHR 27.61, 9.92-76.89), generalized seizure (aHR 7.95, 2.74-23.05), seizure frequency ≥30 times/month (aHR 4.76, 1.27-17.87), and surgical age ≥2 years (aHR 3.78, 1.51-9.47); motor stability was associated with severe motor defects (aHR 5.23, 2.27-12.05) and postoperative seizure-free status (aHR 3.09, 1.49-6.45); and cognition stability was associated with postoperative seizure-free status (aHR 2.84, 1.39-5.78) and surgical age <2 years (aHR 1.76, 1.13-2.75).

DISCUSSION

FR is a valid option for refractory epilepsy in patients with SWS and has similar outcomes to those of HS, with less morbidity associated with refractory epilepsy. Early surgical treatment (under the age of 2 years) leads to better outcomes after HS, but there is insufficient evidence that surgical age affects FR outcomes. These findings warrant future prospective multicenter cohorts with international cooperation and prolonged follow-up in better exploring more precise outcomes and developing prognostic predictive models.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that in children with SWS and refractory seizures, surgical resection-focal, hemispherectomy, or modified hemispherotomy-leads to improved outcomes.

Precision fMRI reveals that the language network exhibits adult-like left-hemispheric lateralization by 4 years of age

Left hemisphere damage in adulthood often leads to linguistic deficits, but many cases of early damage leave linguistic processing preserved, and a functional language system can develop in the right hemisphere. To explain this early apparent equipotentiality of the two hemispheres for language, some have proposed that the language system is bilateral during early development and only becomes left-lateralized with age. We examined language lateralization using functional magnetic resonance imaging with two large pediatric cohorts (total n=273 children ages 4-16; n=107 adults). Strong, adult-level left-hemispheric lateralization (in activation volume and response magnitude) was evident by age 4. Thus, although the right hemisphere can take over language function in some cases of early brain damage, and although some features of the language system do show protracted development (magnitude of language response and strength of inter-regional correlations in the language network), the left-hemisphere bias for language is robustly present by 4 years of age. These results call for alternative accounts of early equipotentiality of the two hemispheres for language.

Concordance of verbal memory and language fMRI lateralization in people with epilepsy

BACKGROUND AND PURPOSE

This work investigates verbal memory functional MRI (fMRI) versus language fMRI in terms of lateralization, and assesses the validity of performing word recognition during the functional scan.

METHODS

Thirty patients with a diagnosis of epilepsy underwent verbal memory, visuospatial memory, and language fMRI. We used word encoding, word recognition, image encoding, and image recognition memory tasks, and semantic description, reading comprehension, and listening comprehension language tasks. We used three common lateralization metrics: network spatial distribution, maximum statistical value, and laterality index (LI).

RESULTS

Lateralization of signal spatial distribution resulted in poor similarity between verbal memory and language fMRI tasks. Signal maximum lateralization showed significant (>.8) but not perfect (1) similarity. Word encoding LI showed significant correlation only with listening comprehension LI (p = .016). Word recognition LI was significantly correlated with expressive language semantic description LI (p = .024) and receptive language reading and listening comprehension LIs (p = .015 and p = .019, respectively). There was no correlation between LIs of the visuospatial tasks and LIs of the language tasks.

CONCLUSIONS

Our results support the association between language and verbal memory lateralization, optimally determined by LI quantification, and the introduction of quantitative means for language fMRI interpretation in clinical settings where verbal memory lateralization is imperative.

Disruption of Cerebellar–Cerebral Functional Connectivity in Temporal Lobe Epilepsy and the Connection to Language and Cognitive Functions

Objective

To investigate the changes in the cerebellar-cerebral language network in temporal lobe epilepsy (TLE) patients from the cerebellar perspective, the research analyzes the changes of language and cognitive network in terms of functional connectivity (FC), as well as their efficiency of the reorganization were evaluated basing on relationship between the network metrics and neuropsychological scale scores.

Methods

30 TLE patients and 30 healthy controls were recruited. Brain activity was evaluated by voxel-mirrored homotopic connectivity analysis (VMHC). Two groups were analyzed and compared in terms of language FC using the following methods: Seed-to-Voxel analysis, pairwise correlations [region of interest(ROI)-to-ROI] and graph theory. Correlation analysis was performed between network properties and neuropsychological score.

Results

Compared with healthy participants, VMHC values in the Cerebellum Anterior Lobe, Frontal Lobe, Frontal_Sup_R/L, Cingulum_Ant_R/L, and Cingulum_Mid_R/L were decreased in TLE patients. Decreased FC was observed from the Cerebelum_10_R to the left inferior frontal gyrus, from the Cerebelum_6_R to the left Lingual Gyrus, from the Cerebelum_4_5_R to left Lingual Gyrus, left Cuneal Cortex and Precuneous Cortex, from the Cerebelum_3_R to Brain-Stem, and from the Cerebelum_Crus1_L to Cerebelum_6_R in TLE patients. The FC was enhanced between bilateral Cingulum_Mid and angular gyrus and frontoparietal insular cranium, between Frontal_Sup_Med L and left/right superior temporal gyrus (pSTG l/r), while it was decreased between left middle temporal gyrus and pSTG l/r. Compared with controls, the Betweenness Centrality (BC) of the right superior marginal gyrus (SMG), Temporal_Pole_Mid_R and Temporal_Mid_L as well as the Degree Centrality (DC) and Nodal Efficiency (NE) of the right SMG were lower in TLE patients. Further analysis showed that decreased VMHC in bilateral Cerebellum Anterior Lobe was positively correlated with the Boston Naming Test score in TLE patients, but it was negatively correlated with the Verbal Fluency Test score. The NE and DC of SMG_R were both negatively correlated with visual perception score in Montreal Cognitive Assessment.

Conclusion

Our results suggest that presence of abnormalities in the static functional connectivity and the language and cognitive network of TLE patients. Cerebellum potentially represents an intervention target for delaying or improving language and cognitive deficits in patients with TLE.

Mapping of Language-and-Memory Networks in Patients With Temporal Lobe Epilepsy by Using the GE2REC Protocol

Preoperative mapping of language and declarative memory functions in temporal lobe epilepsy (TLE) patients is essential since they frequently encounter deterioration of these functions and show variable degrees of cerebral reorganization. Due to growing evidence on language and declarative memory interdependence at a neural and neuropsychological level, we propose the GE2REC protocol for interactive language-and-memory network (LMN) mapping. GE2REC consists of three inter-related tasks, sentence generation with implicit encoding (GE) and two recollection (2REC) memory tasks: recognition and recall. This protocol has previously been validated in healthy participants, and in this study, we showed that it also maps the LMN in the left TLE (N = 18). Compared to healthy controls (N = 19), left TLE (LTLE) showed widespread inter- and intra-hemispheric reorganization of the LMN through reduced activity of regions engaged in the integration and the coordination of this meta-network. We also illustrated how this protocol could be implemented in clinical practice individually by presenting two case studies of LTLE patients who underwent efficient surgery and became seizure-free but showed different cognitive outcomes. This protocol can be advantageous for clinical practice because it (a) is short and easy to perform; (b) allows brain mapping of essential cognitive functions, even at an individual level; (c) engages language-and-memory interaction allowing to evaluate the integrative processes within the LMN; (d) provides a more comprehensive assessment by including both verbal and visual modalities, as well as various language and memory processes. Based on the available postsurgical data, we presented preliminary results obtained with this protocol in LTLE patients that could potentially inform the clinical practice. This implies the necessity to further validate the potential of GE2REC for neurosurgical planning, along with two directions, guiding resection and describing LMN neuroplasticity at an individual level.

Nomograms to Predict Verbal Memory Decline After Temporal Lobe Resection in Adults With Epilepsy

OBJECTIVE

To develop and externally validate models to predict the probability of postoperative verbal memory decline in adults after temporal lobe resection (TLR) for epilepsy using easily accessible preoperative clinical predictors.

METHODS

Multivariable models were developed to predict delayed verbal memory outcome on 3 commonly used measures: Rey Auditory Verbal Learning Test (RAVLT) and Logical Memory (LM) and Verbal Paired Associates (VPA) subtests from Wechsler Memory Scale-Third Edition. With the use of the Harrell step-down procedure for variable selection, models were developed in 359 adults who underwent TLR at the Cleveland Clinic and validated in 290 adults at 1 of 5 epilepsy surgery centers in the United States or Canada.

RESULTS

Twenty-nine percent of the development cohort and 26% of the validation cohort demonstrated significant decline on at least 1 verbal memory measure. Initial models had good to excellent predictive accuracy (calibration [c] statistic range 0.77-0.80) in identifying patients with memory decline; however, models slightly underestimated decline in the validation cohort. Model coefficients were updated with data from both cohorts to improve stability. The model for RAVLT included surgery side, baseline memory score, and hippocampal resection. The models for LM and VPA included surgery side, baseline score, and education. Updated model performance was good to excellent (RAVLT c = 0.81, LM c = 0.76, VPA c = 0.78). Model calibration was very good, indicating no systematic overestimation or underestimation of risk.

CONCLUSIONS

Nomograms are provided in 2 easy-to-use formats to assist clinicians in estimating the probability of verbal memory decline in adults considering TLR for treatment of epilepsy.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that multivariable prediction models accurately predict verbal memory decline after TLR for epilepsy in adults.

Language lateralization differences between left and right temporal lobe epilepsy as measured by overt word reading fMRI activation and DTI structural connectivity

In cases of brain disease such as temporal lobe epilepsy (TLE), damage may lead to functional reorganization and a shift in language dominance to homolog regions in the other hemisphere. If the effects of TLE on language dominance are hemisphere-focused, then brain regions and connections involved in word reading should be less left-lateralized in left temporal lobe epilepsy (lTLE) than right temporal lobe epilepsy (rTLE) or healthy controls, and the opposite effect should be observed in patients with rTLE. In our study, functional magnetic resonance imaging (fMRI) showed that patients with rTLE had more strongly lateralized left hemisphere (LH) activation than patients with lTLE and healthy controls in language-related brain regions (pars opercularis and fusiform gyrus (FuG)). Corresponding with this difference, diffusion tensor imaging (DTI) found differences in connectivity indicative of patients with lTLE having greater tract integrity than patients with rTLE in the right hemisphere (RH) uncinate fasciculus (UF), inferior longitudinal fasciculus (ILF), and inferior fronto-occipital fasciculus (IFOF) using the network-based statistic analysis method. The UF, ILF, and IFOF tract integrity have previously been associated with lexical (whole-word) processing abilities. Multivariate distance matrix regression provided converging evidence for regions of the IFOF having different connectivity patterns between groups with lTLE and rTLE. This research demonstrates language lateralization differences between patient groups with lTLE and rTLE, and corresponding differences in the connectivity strength of the ILF, IFOF, and UF. This research provides a novel approach to measuring lateralization of language in general, and the fMRI and DTI findings were integral for guiding the neurosurgeons performing the TLE resections. This approach should inform future studies of language lateralization and language reorganization in patients such as those with TLE.

High-gamma modulation language mapping with stereo-EEG: A novel analytic approach and diagnostic validation

OBJECTIVE

A novel analytic approach for task-related high-gamma modulation (HGM) in stereo-electroencephalography (SEEG) was developed and evaluated for language mapping.

METHODS

SEEG signals, acquired from drug-resistant epilepsy patients during a visual naming task, were analyzed to find clusters of 50-150 Hz power modulations in time-frequency domain. Classifier models to identify electrode contacts within the reference neuroanatomy and electrical stimulation mapping (ESM) speech/language sites were developed and validated.

RESULTS

In 21 patients (9 females), aged 4.8-21.2 years, SEEG HGM model predicted electrode locations within Neurosynth language parcels with high diagnostic odds ratio (DOR 10.9, p < 0.0001), high specificity (0.85), and fair sensitivity (0.66). Another SEEG HGM model classified ESM speech/language sites with significant DOR (5.0, p < 0.0001), high specificity (0.74), but insufficient sensitivity. Time to largest power change reliably localized electrodes within Neurosynth language parcels, while, time to center-of-mass power change identified ESM sites.

CONCLUSIONS

SEEG HGM mapping can accurately localize neuroanatomic and ESM language sites.

SIGNIFICANCE

Predictive modelling incorporating time, frequency, and magnitude of power change is a useful methodology for task-related HGM, which offers insights into discrepancies between HGM language maps and neuroanatomy or ESM.

Left hemispherectomy in older children and adolescents: outcome of cognitive abilities

PURPOSE

Hemispherectomy is an effective treatment option for pharmacoresistant epilepsy. Nevertheless, when high cortical functions are at risk during the presurgical evaluation, especially for older children, and for the left hemisphere, despite good seizure outcome, the anticipated decrease of cognitive functions may prevent a decision to perform surgery. The objective of this study is to report the cognitive outcome, based on verbal and performance intelligence skills, in a series of older children and adolescents who underwent left hemispherectomy, analyzing the risks (residual cognitive deficit) and benefits (seizure reduction) of surgery.

METHODS

We retrospectively analyzed pre- and postoperative clinical and neuropsychological data from our patients who underwent left hemispherectomy, aged between 6 and 18 years.

RESULTS

We included 15 patients, with a mean follow-up of 3.1 years, 12 patients (80%) were Engel I, and the other three were classified as Engel II, III, and IV. Nine patients were tested by Wechsler Scales of Intelligence; postsurgically all but one kept the same intellectual levels; verbal intelligence quotient (VIQ) remained unchanged in 13 and improved in one, whereas performance intelligence quotient (PIQ) decreased in four patients. Both Total Vineland and communication scores of Vineland Adaptive Behavior Scales were obtained in six patients: in all, scores were classified as deficient adaptive functioning pre- and postoperatively, remaining unchanged.

CONCLUSION

The evaluation of the remaining intellectual abilities after left hemispherectomy in older children and adolescents is useful to discuss the risks and benefits of this surgery, enabling better and safer decisions regarding surgical indications and timing.

Atypical language localization in right temporal lobe epilepsy: An fMRI case report

We report a 41- year-old, left-handed patient with drug-resistant right temporal lobe epilepsy (TLE). Presurgical fMRI was conducted to examine whether the patient had language functioning in the right hemisphere given that left-handedness is associated with a higher prevalence of right hemisphere dominance for language. The fMRI results revealed bilateral activation in Broca's and Wernicke's areas and activation of eloquent cortex near the region of planned resection in the right temporal lobe. Due to right temporal language-related activation, the patient underwent an awake right-sided temporal lobectomy with intraoperative language mapping. Intraoperative direct cortical stimulation (DCS) was conducted in the regions corresponding to the fMRI activation, and the patient showed language abnormalities, such as paraphasic errors, and speech arrest. The decision was made to abort the planned anterior temporal lobe procedure, and the patient instead underwent a selective amygdalohippocampectomy via the Sylvian fissure at a later date. Post-operatively the patient was seizure-free with no neurological deficits. Taken together, the results support previous findings of right hemisphere language activation in left-handed individuals, and should be considered in cases in which presurgical localization is conducted for left-hand dominant patients undergoing neurosurgical procedures.

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The report evaluates evidence for the possibility of right hemisphere language activation in a left-handed right TLE patient

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The results of the fMRI tasks showed bilateral speech regions, such as left and right Broca's area and Wernicke's area

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The results support previous findings of right hemisphere language activation in left-handed individuals

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The report discusses the value of fMRI of language tasks for presurgical planning in epilepsy cases

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Report highlights how fMRI findings can alter surgical strategy and how intraoperative brain mapping validates these findings

A model for visual naming based on spatiotemporal dynamics of ECoG high-gamma modulation

OBJECTIVE

We studied spatiotemporal dynamics of electrocorticographic (ECoG) high-gamma modulation (HGM) during visual naming.

METHODS

In 8 patients, aged 4-19 years, with left hemisphere subdural electrodes, propagation of ECoG HGM during overt visual naming was mapped with trial-averaged time-frequency analysis. Group-level synthesis was performed by transforming all electrodes to a standard space and assigning cortical parcels based on a reference atlas.

RESULTS

After image display following cortical parcels were activated: inferior occipital, caudal angular, fusiform, and middle temporal gyri, and superior temporal sulcus [0-400 ms]; rostral pars triangularis (A45r), inferior frontal sulcus, caudal dorsolateral premotor cortex (A6cdl) [300-600 ms]; caudal ventrolateral premotor cortex (A6cvl), caudal pars triangularis (A45c), pars opercularis (A44) [400-800 ms]; primary sensorimotor cortex [600-1400 ms], with most prominent HGM in glossolaryngeal region (A4tl). Lastly, auditory cortex (A41/A42) and superior temporal gyrus (A22) were activated [900 ms-1.4 s]. After 1.5 s, HGM decreased globally, except in ventrolateral premotor cortex.

CONCLUSIONS

During visual naming, ECoG HGM shows a sequential but overlapping spatiotemporal course through cortical regions. We provide neurophysiologic validation for a model of visual naming incorporating both modular and distributed cortical processing. This may explain cognitive deficits seen in some patients after surgery involving HGM naming sites outside perisylvian language cortex.

Emotional asymmetries in refractory medial temporal and frontal lobe epilepsy: Their impact on predicting lateralization and localization of seizures

BACKGROUND

Emotional disturbances have been reported in patients with epilepsy. Although conflicting results emanate from relevant studies, depressive symptoms are seen more often in temporal lobe epilepsy (TLE) whereas, hypomanic/manic symptoms usually accompany frontal lobe epilepsy (FLE); the above psychiatric symptoms are especially seen in refractory epilepsy. However, neocortical TLE and medial TLE are considered as distinct epileptic syndromes, and there is limited literature on comparison of affective traits in medial TLE (MTLE) and FLE.

AIM

In the present study, we sought to investigate affective traits among epilepsy surgery candidates suffering refractory left medial TLE (LMTLE), right medial TLE (RMTLE), left FLE (LFLE), and right FLE (RFLE).

RESULTS

Our results revealed that patients with MTLE scored significantly higher than the ones with FLE in depression, anxiety, asthenia, and melancholia as measured by the Symptoms Rating Scale for Depression and Anxiety (SRSDA), while patients with FLE scored significantly higher in mania than those with MTLE. Moreover, patients with MTLE scored significantly higher than their FLE counterparts on the anxiety scale of the State Trait Personality Inventory (STPI)-trait version. When laterality of the seizure focus was taken into account, no differences were found among both patients with MTLE and patients with FLE, with exception for the Trail Making Test part B (TMT-B) in which patients with RMTLE performed significantly worse than patients with LMTLE. Seizure frequency was higher for FLE.

CONCLUSIONS

We provide evidence for an anterior-frontal versus a posterior-medial temporal cerebral functional asymmetry with regard to the manifestation of manic and depressive emotional traits in FLE and MTLE, respectively. Our results are mainly discussed within the frame of their contribution in localizing and to a lesser extent in lateralizing seizures foci in epilepsy surgery candidates. We suggest that this is of great importance in the context of preoperative monitoring of epilepsy surgery, especially when neuropsychologists are called upon to provide anatomical information in defining the functional deficit zone.

Re-examining the crowding hypothesis in pediatric epilepsy

OBJECTIVE

In adults with left-sided epilepsy, reorganized language may "crowd out" right-hemisphere visual-spatial skills, with relative sparing of language (i.e., the crowding hypothesis). However, this effect has not consistently been demonstrated in pediatric epilepsy studies. The objective of this study was to investigate the crowding hypothesis using a heterogeneous sample of children with intractable epilepsy and typical (left) language dominance or atypical (right or bilateral) language dominance. We examined the relative contributions of seizure onset (before or after age 5), handedness (right versus left), seizure localization (temporal versus extratemporal), as well as language dominance on verbal versus visual cognitive skills.

METHOD

We retrospectively analyzed neuropsychology assessment results from a sample of 91 children who completed presurgical evaluation at the Hospital for Sick Children in Toronto, Canada (34 with typical language, 57 with atypical language, mean age = 12 years). We considered a selection of verbal skills (naming, vocabulary knowledge, verbal abstract reasoning) and visual skills (visual-motor integration, block construction, visual abstract reasoning).

RESULTS

Consistent with several previous adult studies supporting the crowding hypothesis, univariate analyses showed that the typical and atypical language groups were comparable on the measures of vocabulary knowledge and abstract verbal reasoning whereas the atypical language group produced lower scores across visual measures. Multivariate analyses (taking into account language dominance and associated factors) showed that language dominance was the strongest predictor of performance on two of three visual measures whereas language dominance was not a significant predictor of performance on most verbal measures. Unexpectedly, both sets of analyses indicated that the atypical language group had poorer naming abilities than the typical language group.

SIGNIFICANCE

Our data provide some evidence of right-hemisphere functional crowding effects in a heterogeneous sample of children with intractable left-sided epilepsy. Specifically, those with atypical versus typical language dominance showed poorer visual-motor integration and visual-motor problem-solving skills, with comparable scores on certain verbal measures. It is critical that potential crowding effects be considered when interpreting the neuropsychological profiles of children being evaluated for epilepsy surgery.

Nomograms to predict naming decline after temporal lobe surgery in adults with epilepsy

OBJECTIVE

To develop and externally validate models to predict the probability of postoperative naming decline in adults following temporal lobe epilepsy surgery using easily accessible preoperative clinical predictors.

METHODS

In this retrospective, prediction model development study, multivariable models were developed in a cohort of 719 patients who underwent temporal lobe epilepsy surgery at Cleveland Clinic and externally validated in a cohort of 138 patients who underwent temporal lobe surgery at one of 3 epilepsy surgery centers in the United States (Columbia University Medical Center, Emory University School of Medicine, University of Washington School of Medicine).

RESULTS

The development cohort was 54% female with an average age at surgery of 36 years (SD 12). Twenty-six percent of this cohort experienced clinically relevant postoperative naming decline. The model included 5 variables: side of surgery, age at epilepsy onset, age at surgery, sex, and education. When applied to the external validation cohort, the model performed very well, with excellent calibration and a c statistic (reflecting discriminatory ability) of 0.81. A second model predicting moderate to severe postoperative naming decline included 3 variables: side of surgery, age at epilepsy onset, and preoperative naming score. This model generated a c statistic of 0.84 in the external validation cohort and showed good calibration.

CONCLUSION

Externally validated nomograms are provided in 2 easy-to-use formats (paper version and online calculator) clinicians can use to estimate the probability of naming decline in patients considering epilepsy surgery for treatment of pharmacoresistant temporal lobe epilepsy.

Machine learning-XGBoost analysis of language networks to classify patients with epilepsy

Our goal was to apply a statistical approach to allow the identification of atypical language patterns and to differentiate patients with epilepsy from healthy subjects, based on their cerebral activity, as assessed by functional MRI (fMRI). Patients with focal epilepsy show reorganization or plasticity of brain networks involved in cognitive functions, inducing ‘atypical’ (compared to ‘typical’ in healthy people) brain profiles. Moreover, some of these patients suffer from drug-resistant epilepsy, and they undergo surgery to stop seizures. The neurosurgeon should only remove the zone generating seizures and must preserve cognitive functions to avoid deficits. To preserve functions, one should know how they are represented in the patient’s brain, which is in general different from that of healthy subjects. For this purpose, in the pre-surgical stage, robust and efficient methods are required to identify atypical from typical representations. Given the frequent location of regions generating seizures in the vicinity of language networks, one important function to be considered is language. The risk of language impairment after surgery is determined pre-surgically by mapping language networks. In clinical settings, cognitive mapping is classically performed with fMRI. The fMRI analyses allowing the identification of atypical patterns of language networks in patients are not sufficiently robust and require additional statistic approaches. In this study, we report the use of a statistical nonlinear machine learning classification, the Extreme Gradient Boosting (XGBoost) algorithm, to identify atypical patterns and classify 55 participants as healthy subjects or patients with epilepsy. XGBoost analyses were based on neurophysiological features in five language regions (three frontal and two temporal) in both hemispheres and activated with fMRI for a phonological (PHONO) and a semantic (SEM) language task. These features were combined into 135 cognitively plausible subsets and further submitted to selection and binary classification. Classification performance was scored with the Area Under the receiver operating characteristic curve (AUC). Our results showed that the subset SEM_LH BA_47-21 (left fronto-temporal activation induced by the SEM task) provided the best discrimination between the two groups (AUC of 91 ± 5%). The results are discussed in the framework of the current debates of language reorganization in focal epilepsy.

Disrupted functional connectivity affects resting state based language lateralization

Pre-operative assessment of language localization and lateralization is critical to preserving brain function after lesion or epileptogenic tissue resection. Task fMRI (t-fMRI) has been extensively and reliably used to this end, but resting state fMRI (rs-fMRI) is emerging as an alternative pre-operative brain mapping method that is independent of a patient's ability to comply with a task. We sought to evaluate if language lateralization obtained from rs-fMRI can replace standard assessment using t-fMRI. In a group of 43 patients scheduled for pre-operative fMRI brain mapping and 17 healthy controls, we found that existing methods of determining rs-fMRI lateralization by considering interhemispheric and intrahemispheric functional connectivity are inadequate compared to t-fMRI when applied to the language network. We determined that this was attributable to widespread but nuanced disturbances in the functional connectivity of the language network in patients. We found changes in interhemispheric and intrahemispheric functional connectivity that were dependent on lesion location, and particularly impacted patients with lesions in the left temporal lobe. We then tested whether a simpler measure of functional connectivity to the language network has a better relation to t-fMRI based language lateralization. Remarkably, we found that functional connectivity between the language network and the frontal pole, and superior frontal gyrus, as well as the supramarginal gyrus, significantly correlated to task based language lateralization indices in both patients and healthy controls. These findings are consistent with prior work with epilepsy patients, and provide a framework for evaluating language lateralization at rest.

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Existing methods of determining rs-fMRI lateralization are inadequate for language.

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Functional connectivity to language network correlates with task lateralization.

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Lesion location affects functional connectivity.

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Lesions exhibit some interhemispheric hyperconnectivity within language network.

Sex differences in lateralization of semantic verbal fluency in temporal lobe epilepsy

When differences exist, women tend to outperform men on measures of verbal fluency, possibly due to greater bilateral language representation. Patients with temporal lobe epilepsy (TLE) have a higher rate of atypical cortical language representation than the general population, making them a population of interest for the study of language. For the current study, 78 TLE patients (51% male, 51% left temporal focus) underwent pre-surgical neuropsychological evaluations. Retrospective data analyses investigated the impact of seizure laterality and sex on letter and semantic verbal fluency. Results indicated an interaction between sex and laterality for semantic, but not letter, verbal fluency. Males with left TLE exhibited significantly worse semantic fluency than males with right TLE, whereas females' semantic fluency did not differ by seizure focus. These data indicate that females with TLE may indeed engage in more bilateral hemispheric processing of semantic verbal fluency, whereas males may be more reliant on left temporal cortical function for this task.

Resting-state functional magnetic resonance imaging: review of neurosurgical applications

Recent research in brain imaging has highlighted the role of different neural networks in the resting state (ie, no task) in which the brain displays spontaneous low-frequency neuronal oscillations. These can be indirectly measured with resting-state functional magnetic resonance imaging, and functional connectivity can be inferred as the spatiotemporal correlations of this signal. This technique has proliferated in recent years and has allowed the noninvasive investigation of large-scale, distributed functional networks. In this review, we give a brief overview of resting-state networks and examine the use of resting-state functional magnetic resonance imaging in neurosurgical contexts, specifically with respect to neurooncology, epilepsy surgery, and deep brain stimulation. We discuss the advantages and disadvantages compared with task-based functional magnetic resonance imaging, the limitations of resting-state functional magnetic resonance imaging, and the emerging directions of this relatively new technology.

Electrocorticographic language mapping in children by high-gamma synchronization during spontaneous conversation: comparison with conventional electrical cortical stimulation

INTRODUCTION

This study describes development of a novel language mapping approach using high-γ modulation in electrocorticograph (ECoG) during spontaneous conversation, and its comparison with electrical cortical stimulation (ECS) in childhood-onset drug-resistant epilepsy.

METHODS

Patients undergoing invasive pre-surgical monitoring and able to converse with the investigator were eligible. ECoG signals and synchronized audio were acquired during quiet baseline and during natural conversation between investigator and the patient. Using Signal Modeling for Real-time Identification and Event Detection (SIGFRIED) procedure, a statistical model for baseline high-γ (70-116 Hz) power, and a single score for each channel representing the probability that the power features in the experimental signal window belonged to the baseline model, were calculated. Electrodes with significant high-γ responses (HGS) were plotted on the 3D cortical model. Sensitivity, specificity, positive and negative predictive values (PPV, NPV), and classification accuracy were calculated compared to ECS.

RESULTS

Seven patients were included (4 males, mean age 10.28 ± 4.07 years). Significant high-γ responses were observed in classic language areas in the left hemisphere plus in some homologous right hemispheric areas. Compared with clinical standard ECS mapping, the sensitivity and specificity of HGS mapping was 88.89% and 63.64%, respectively, and PPV and NPV were 35.29% and 96.25%, with an overall accuracy of 68.24%. HGS mapping was able to correctly determine all ECS+ sites in 6 of 7 patients and all false-sites (ECS+, HGS- for visual naming, n = 3) were attributable to only 1 patient.

CONCLUSIONS

This study supports the feasibility of language mapping with ECoG HGS during spontaneous conversation, and its accuracy compared to traditional ECS. Given long-standing concerns about ecological validity of ECS mapping of cued language tasks, and difficulties encountered with its use in children, ECoG mapping of spontaneous language may provide a valid alternative for clinical use.

Functional language shift to the right hemisphere in patients with language-eloquent brain tumors

Objectives

Language function is mainly located within the left hemisphere of the brain, especially in right-handed subjects. However, functional MRI (fMRI) has demonstrated changes of language organization in patients with left-sided perisylvian lesions to the right hemisphere. Because intracerebral lesions can impair fMRI, this study was designed to investigate human language plasticity with a virtual lesion model using repetitive navigated transcranial magnetic stimulation (rTMS).

Experimental design

Fifteen patients with lesions of left-sided language-eloquent brain areas and 50 healthy and purely right-handed participants underwent bilateral rTMS language mapping via an object-naming task. All patients were proven to have left-sided language function during awake surgery. The rTMS-induced language errors were categorized into 6 different error types. The error ratio (induced errors/number of stimulations) was determined for each brain region on both hemispheres. A hemispheric dominance ratio was then defined for each region as the quotient of the error ratio (left/right) of the corresponding area of both hemispheres (ratio >1  =  left dominant; ratio <1  =  right dominant).

Results

Patients with language-eloquent lesions showed a statistically significantly lower ratio than healthy participants concerning “all errors” and “all errors without hesitations”, which indicates a higher participation of the right hemisphere in language function. Yet, there was no cortical region with pronounced difference in language dominance compared to the whole hemisphere.

Conclusions

This is the first study that shows by means of an anatomically accurate virtual lesion model that a shift of language function to the non-dominant hemisphere can occur.

Brain activation associated with practiced left hand mirror writing

Mirror writing occurs in healthy children, in various pathologies and occasionally in healthy adults. There are only scant experimental data on the underlying brain processes. Eight, right-handed, healthy young adults were scanned (BOLD-fMRI) before and after practicing left-hand mirror-writing (lh-MW) over seven sessions. They wrote dictated words, using either the right hand with regularly oriented writing or lh-MW. An MRI compatible stylus-point recording system was used and online visual feedback was provided. Practice resulted in increased speed and readability of lh-MW but the number of movement segments was unchanged. Post-training signal increases occurred in visual, right lateral and medial premotor areas, and in right anterior and posterior peri-sylvian areas corresponding to language areas. These results suggest that lh-MW may constitute a latent ability that can be reinstated by a relatively brief practice experience. Concurrently, right hemisphere language processing areas may emerge, reflecting perhaps a reduction in trans-hemispheric suppression.

Defining language networks from resting-state fMRI for surgical planning--a feasibility study

Presurgical language mapping for patients with lesions close to language areas is critical to neurosurgical decision-making for preservation of language function. As a clinical noninvasive imaging technique, functional MRI (fMRI) is used to identify language areas by measuring blood-oxygen-level dependent (BOLD) signal change while patients perform carefully timed language vs. control tasks. This task-based fMRI critically depends on task performance, excluding many patients who have difficulty performing language tasks due to neurologic deficits. On the basis of recent discovery of resting-state fMRI (rs-fMRI), we propose a "task-free" paradigm acquiring fMRI data when patients simply are at rest. This paradigm is less demanding for patients to perform and easier for technologists to administer. We investigated the feasibility of this approach in right-handed healthy control subjects. First, group independent component analysis (ICA) was applied on the training group (14 subjects) to identify group level language components based on expert rating results. Then, four empirically and structurally defined language network templates were assessed for their ability to identify language components from individuals' ICA output of the testing group (18 subjects) based on spatial similarity analysis. Results suggest that it is feasible to extract language activations from rs-fMRI at the individual subject level, and two empirically defined templates (that focuses on frontal language areas and that incorporates both frontal and temporal language areas) demonstrated the best performance. We propose a semi-automated language component identification procedure and discuss the practical concerns and suggestions for this approach to be used in clinical fMRI language mapping.

Homotopic language reorganization in the right hemisphere after early left hemisphere injury

To determine the areas involved in reorganization of language to the right hemisphere after early left hemisphere injury, we compared fMRI activation patterns during four production and comprehension tasks in post-surgical epilepsy patients with either left (LH) or right hemisphere (RH) speech dominance (determined by Wada testing) and healthy controls. Patient groups were carefully matched for IQ, lesion location and size. RH patients' activation across all tasks was greatest in right hemisphere areas homotopic to areas activated by LH and control participants. Differences in right vs. left dominant hemisphere activation were limited to homologous areas typically activated by language tasks, supporting the hypothesis that language localization following transfer to the RH is the mirror-image of localization in the absence of transfer. The similarity of these findings to those in patients with larger, peri-sylvian lesions suggests that these areas in both hemispheres may be uniquely predisposed to subserve various language functions.

Functional MRI and neuropsychological evidence for language plasticity before and after surgery in one patient with left temporal lobe epilepsy

This study explores the language reorganization before and after surgery in a 55-year-old right-handed female patient presenting with left temporal refractory epilepsy. Two aspects of language were explored, phonological and semantic, by using neuropsychological assessments and fMRI protocols. To assess the possible reorganization of language, fMRI results for B.L. were compared with results obtained in a group of healthy control subjects (results not presented in detail). According to our results and compared with healthy subjects, B.L. shows reorganization of temporal regions only. The reorganization had various patterns according to the task. Before surgery, neuropsychological testing in B.L. revealed impairment in phonological abilities and fMRI suggested right temporal involvement (interhemisphere reorganization) during the phonological task; semantic abilities were unaltered and fMRI showed bilateral activation of temporal regions during the semantic task. After surgery, the phonological deficit disappeared and fMRI showed left perilesional location of temporal activation (intrahemispheric reorganization); semantic abilities remain preserved and temporal activation remained located bilaterally but predominantly to the right during the semantic task. Our results suggest that cerebral reorganization of language depends on the language operation tested. Moreover, the results underline the importance of differential assessment of language operations and show functional reorganization after beneficial surgery in an older patient.

Cerebral plasticity and recovery of function after childhood prefrontal cortex damage

OBJECTIVE

Recovery of function after early brain injury depends upon both reparative and compensatory processes that are minimally understood. Using functional magnetic resonance imaging (fMRI), this study investigated the reorganization of hemispheric brain activity of a 24 year old male who suffered right prefrontal cortex damage at 7 years of age related to ruptured arteriovenous malformation. His pattern of recovery has been examined and tracked over the past 17 years and evolved from initial significant impairments in executive, spatial and attentional abilities from the brain lesion to remarkable recovery of function.

METHODS

High field fMRI studies were completed with experimental cognitive tasks sensitive to right prefrontal functions, including visuospatial relational reasoning, spatial working memory, go no-go, emotional face recognition, and coin calculation. RESULTS were compared to a matched control group for total hemispheric activity patterns.

RESULTS

Analyses revealed that on fMRI activation tasks where the patient scored similar to controls, he activated a broader network of bilateral cortical regions than controls. On tasks where he scored lower than controls, there was under-activation of prefrontal cortical regions in comparison to controls.

CONCLUSION

Recovery of function after prefrontal cortex damage in childhood can occur and be associated with significant functional reorganization of hemispheric activity patterns (i.e. developmental cerebral plasticity). Although not all tasks showed recovery to the same extent in this case, those tasks with the most robust recovery entailed compensatory activation of additional cortical regions on fMRI. Further studies are needed to confirm and extend these findings.

Threshold-independent functional MRI determination of language dominance: a validation study against clinical gold standards

Functional MRI (fMRI) is often used for presurgical language lateralization. In the most common approach, a laterality index (LI) is calculated on the basis of suprathreshold voxels. However, strong dependencies between LI and threshold can diminish the effectiveness of this technique; in this study we investigated an original methodology that is independent of threshold. We compared this threshold-independent method against the common threshold-dependent method in 14 patients with epilepsy who underwent Wada testing. In addition, clinical results from electrocortical language mapping and postoperative language findings were used to assess the validity of the fMRI lateralization method. The threshold-dependent methodology yielded ambiguous or incongruent lateralization outcomes in 4 of 14 patients in the inferior frontal gyrus (IFG) and in 6 of 14 patients in the supramarginal gyrus (SMG). Conversely, the threshold-independent method yielded unambiguous lateralization in all the patients tested, and demonstrated lateralization outcomes incongruent with clinical standards in 2 of 14 patients in IFG and in 1 of 14 patients in SMG. This validation study demonstrates that the threshold-dependent LI calculation is prone to significant within-patient variability that could render results unreliable; the threshold-independent method can generate distinct LIs that are more concordant with gold standard clinical findings.

Functional MRI evidence for language plasticity in adult epileptic patients: Preliminary results

The present fMRI study explores the cerebral reorganisation of language in patients with temporal lobe epilepsy, according to the age of seizures onset (early or late) and the hippocampal sclerosis (associated or not). Seven right-handed control volunteers and seven preoperative adult epileptic patients performed a rhyme decision (language condition) and a visual detection (control condition) tasks in visually presented words and unreadable characters, respectively. All patients were left hemisphere dominant for language. Appropriate statistical analyses provided the following preliminary results: (1) patients compared with healthy subjects showed lower degree of hemispheric lateralization with supplementary involvement of the right hemisphere; (2) the degree of hemispheric specialization depends on the considered region; (3) patients with early seizures show signs of temporal and parietal reorganization more frequently than patients with late onset of seizures; (4) patients with early seizures show a tendency for intra-hemispheric frontal reorganisation; (5) associated hippocampal sclerosis facilitates the inter-hemispheric shift of temporal activation. Although our patients were left hemisphere predominant for language, the statistical analyses indicated that the degree of lateralization was significantly lower than in healthy subjects. This result has been considered as the indication of atypical lateralization of language.

Functional MRI approach for assessing hemispheric predominance of regions activated by a phonological and a semantic task

This fMRI study performed in healthy subjects aimed at using a statistical approach in order to determine significant functional differences between hemispheres and to assess specialized regions activated during a phonological and during a semantic task. This approach ("flip" method and subsequent statistical analyses of the parameter estimates extracted from regions of interest) allows identifying: (a) hemispheric specialized regions for each language task [semantic (living categorization) and phonological (rhyme detection)] and (b) condition-specific regions with respect to paradigm conditions (task and control). Our results showed that the rhyme-specific task regions were the inferior frontal (sub-region of BA 44, 45) and left inferior parietal (BA 40, 39) lobules. Furthermore, within the inferior parietal lobule, the angular gyrus was specific to target (rhyming) items (related to successfully grapho-phonemic processing). The categorization-specific task regions were the left inferior frontal (sub-region of BA 44, 45) and superior temporal (BA 22) cortices. Furthermore, the superior temporal gyrus was related to non-target (non-living) items (correlated to task difficulty). The relatively new approach used in this study has the advantage of providing: (a) statistical significance of the hemispheric specialized regions for a given language task and (b) supplementary information in terms of paradigm condition-specificity of the activated regions. The results (standard hemispheric specialized regions for a semantic and for a phonological task) obtained in healthy subjects may constitute a basement for mapping language and assessing hemispheric predominance in epileptic patients before surgery and avoiding post-surgical impairments of language.

Frontoparietal activation during delayed visuospatial recall in patients with epilepsy due to hippocampal sclerosis

We hypothesized that brain activation during encoding and retrieval of visual material differed between epilepsy patients with hippocampal sclerosis (HS) and healthy controls. Eleven patients with epilepsy and HS and nine age- and education-matched control subjects were tested during functional MRI recording. A three-block design for visuospatial memory encoding and retrieval and an interference interval longer than 1 minute without memory tasks were used. All subjects revealed parietal, occipital, and prefrontal activation patterns during encoding. Interference revealed parietal more than occipital activation, whereas retrieval revealed asymmetrical frontal and parietal activation. Patients demonstrated a relative increase in occipitoparietal versus frontal cortical activation as compared with controls. Memory performance did not differ between patients and controls. The increased activation in occipitoparietal versus frontal areas in the patients suggests cortical reorganization of visuospatial recognition memory in epilepsy patients with HS. The study is limited by other factors that may contribute to the results, for example, antiepileptic drugs, effects of greater cognitive effort allocated in patients than controls, and possibly subclinical epileptic activity. However, normal visuospatial memory performance in our patients with HS suggests successful network plasticity.