Cerebral lesions can impair fMRI-based language lateralization

Functional location of the language cortical areas in focal refractory epilepsy using the conventional, selective, and supraselective Wada test

In refractory focal epilepsy, resective surgery offers an alternative for seizure control. However, there is a risk of language deterioration when the epileptogenic zone involves an eloquent cortical region. The Wada test involves the insertion of a catheter through the internal carotid artery and the injection of a short-acting anesthetic, resulting in transient loss of hemisphere function. While its specificity is high, its sensitivity is reduced, despite its limited or absent spatial resolution. Additionally, the generalized action of the anesthetic may lead to misinterpretations due to global cognitive arrest, particularly in patients with baseline deficits. The aim of this report was to prove the refinement of the selective and supraselective protocols, as well as their contribution to overcoming these disadvantages. The procedure began by placing a microcatheter in progressively more distal irrigation sites, according to the required technique, gradually performing angiography with contrast medium. Tissue perfusion allowed the identification of the cerebral parenchyma where the anesthetic would act. After injection, the assessment of neurocognitive changes was conducted. The characterization of language patterns was performed, delineating indispensable eloquent zones and dispensable eloquent zones, irrespective of the patients' cognitive condition. There was concordance between the findings and post-surgical results. The selective and supraselective Wada test surpasses the disadvantages of the conventional method and proves decisive in surgical planning and decision-making.

Assessing Language Lateralization through Gray Matter Volume: Implications for Preoperative Planning in Brain Tumor Surgery

BACKGROUND/OBJECTIVES

Functional MRI (fMRI) is widely used to assess language lateralization, but its application in patients with brain tumors can be hindered by cognitive impairments, compensatory neuroplasticity, and artifacts due to patient movement or severe aphasia. Gray matter volume (GMV) analysis via voxel-based morphometry (VBM) in language-related brain regions may offer a stable complementary approach. This study investigates the relationship between GMV and fMRI-derived language lateralization in healthy individuals and patients with left-hemisphere brain tumors, aiming to enhance accuracy in complex cases.

METHODS

The MRI data from 22 healthy participants and 28 individuals with left-hemisphere brain tumors were analyzed. Structural T1-weighted and functional images were obtained during three language tasks. Language lateralization was assessed based on activation in predefined regions of interest (ROIs), categorized as typical (left) or atypical (right or bilateral). The GMV in these ROIs was measured using VBM. Linear regressions explored GMV-lateralization associations, and logistic regressions predicted the lateralization based on the GMV.

RESULTS

In the healthy participants, typical left-hemispheric language dominance correlated with higher GMV in the left pars opercularis of the inferior frontal gyrus. The brain tumor participants with atypical lateralization showed increased GMV in six right-hemisphere ROIs. The GMV in the language ROIs predicted the fMRI language lateralization, with AUCs from 80.1% to 94.2% in the healthy participants and 78.3% to 92.6% in the tumor patients.

CONCLUSIONS

GMV analysis in language-related ROIs effectively complements fMRI for assessing language dominance, particularly when fMRI is challenging. It correlates with language lateralization in both healthy individuals and brain tumor patients, highlighting its potential in preoperative language mapping. Further research with larger samples is needed to refine its clinical utility.

Noninvasive Prediction of Language Lateralization Through Arcuate Fasciculus Tractography in Patients With Low-Grade Gliomas: Correlation With The Wada Test

Language lateralization is unique to humans, so clarifying dominant side is helpful for removing gliomas involving language areas. This study investigated the arcuate fasciculus (AF) reconstructed by diffusion tensor imaging–based tractography (DTT) in predicting language lateralization in patients with low-grade gliomas. Wada test was performed to determine the language Dominant Hemisphere (DH) and the Contralateral Hemisphere. DTI data [1.5-T magnetic resonance imaging (MRI)] was used to reconstruct AF by two independent operators using a DTT method. Fiber number, volume, and fractional anisotropy (FA) of bilateral reconstructed AF were measured. Lateralization indexes (LIs), including Number Index (NI), Volume Index (VI), and FA Index (FI), were accordingly calculated by mean values. A total of 21 patients with WHO Grade II gliomas in the left hemisphere were included. Every patient received a successful Wada test and reconstruction of bilateral AF. DTT metrics of reconstructed AF, such as fiber number, volume, and FA, showed significantly asymmetric between hemispheres. All the LI (NI, VI, and FI) values were statistically higher in the DH determined by the Wada test. No discrepancy was found between the prediction using the cutoff values of DTT metrics and the results of WADA test. The Kappa values were 0.829, 0.696, and 0.611, indicating NI and VI as more reliable predictor than FI although FI itself may also be feasible. Compared with the Wada test, we consider that DTT of AF is a non-invasive, simple, relatively accurate, and feasible method in predicting language lateralization in patients with low-grade gliomas.

The impact of hippocampal impairment on task-positive and task-negative language networks in temporal lobe epilepsy

OBJECTIVE

To study hippocampal integration within task-positive and task-negative language networks and the impact of a diseased left and right hippocampus on the language connectome in temporal lobe epilepsy (TLE).

METHODS

We used functional magnetic resonance imaging (fMRI) to study a homogenous group of 32 patients with TLE (17 left) and 14 healthy controls during a verb-generation task. We performed functional connectivity analysis and quantified alterations within the language connectome and evaluated disruptions of the functional dissociation along the anterior-posterior axis of the hippocampi.

RESULTS

Connectivity analysis revealed significant differences between left and right TLE compared to healthy controls. Left TLE showed widespread impairment of task-positive language networks, while right TLE showed less pronounced alterations. Particularly right TLE showed altered connectivity for cortical regions that were part of the default mode network (DMN). Left TLE showed a disturbed functional dissociation pattern along the left hippocampus to left and right inferior frontal language regions, while left and right TLE revealed an altered dissociation pattern along the right hippocampus to regions associated with the DMN.

CONCLUSIONS

Our results showed an impaired hippocampal integration into active language and the default mode networks, which both may contribute to language impairment in TLE.

SIGNIFICANCE

Our results emphasize the direct role of the left hippocampus in language processing, and the potential role of the right hippocampus as a modulator between DMN and task-positive networks.

Neuroimaging in Pediatric Epilepsy

Pediatric epilepsy presents with various diagnostic challenges. Recent advances in neuroimaging play an important role in the diagnosis, management and in guiding the treatment of pediatric epilepsy. Structural neuroimaging techniques such as CT and MRI can identify underlying structural abnormalities associated with epileptic focus. Functional neuroimaging provides further information and may show abnormalities even in cases where MRI was normal, thus further helping in the localization of the epileptogenic foci and guiding the possible surgical management of intractable/refractory epilepsy when indicated. A multi-modal imaging approach helps in the diagnosis of refractory epilepsy. In this review, we will discuss various imaging techniques, as well as aspects of structural and functional neuroimaging and their application in the management of pediatric epilepsy.

Characterising neural plasticity at the single patient level using connectivity fingerprints

The occurrence of wide-scale neuroplasticity in the injured human brain raises hopes for biomarkers to guide personalised treatment. At the individual level, functional reorganisation has proven challenging to quantify using current techniques that are optimised for population-based analyses. In this cross-sectional study, we acquired functional MRI scans in 44 patients (22 men, 22 women, mean age: 39.4 ± 14 years) with a language-dominant hemisphere brain tumour prior to surgery and 23 healthy volunteers (11 men, 12 women, mean age: 36.3 ± 10.9 years) during performance of a verbal fluency task. We applied a recently developed approach to characterise the normal range of functional connectivity patterns during task performance in healthy controls. Next, we statistically quantified differences from the normal in individual patients and evaluated factors driving these differences. We show that the functional connectivity of brain regions involved in language fluency identifies “fingerprints” of brain plasticity in individual patients, not detected using standard task-evoked analyses. In contrast to healthy controls, patients with a tumour in their language dominant hemisphere showed highly variable fingerprints that uniquely distinguished individuals. Atypical fingerprints were influenced by tumour grade and tumour location relative to the typical fluency-activated network. Our findings show how alterations in brain networks can be visualised and statistically quantified from connectivity fingerprints in individual brains. We propose that connectivity fingerprints offer a statistical metric of individually-specific network organisation through which behaviourally-relevant adaptations could be formally quantified and monitored across individuals, treatments and time.

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Personalised treatment awaits individualised measures of brain adaptation.

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Connectivity patterns from FMRI offer unique “fingerprints” of brain networks.

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Individual brain tumours disrupt the language fluency network in unique ways.

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By fingerprint matching, networks can be tested and visualised in single patients.

MEG Assessment of Expressive Language in Children Evaluated for Epilepsy Surgery

Establishing language dominance is an important step in the presurgical evaluation of patients with refractory epilepsy. In the absence of a universally accepted gold-standard non-invasive method to determine language dominance in the preoperative assessment, a range of tools and methodologies have recently received attention. When applied to pediatric age, many of the proposed methods, such as functional magnetic resonance imaging (fMRI), may present some challenges due to the time-varying effects of epileptogenic lesions and of on-going seizures on maturational phenomena. Magnetoencephalography (MEG) has the advantage of being insensitive to the distortive effects of anatomical lesions on brain microvasculature and to differences in the metabolism or vascularization of the developing brain and also provides a less intimidating recording environment for younger children. In this study we investigated the reliability of lateralized synchronous cortical activation during a verb generation task in a group of 28 children (10 males and 18 females, mean age 12 years) with refractory epilepsy who were evaluated for epilepsy surgery. The verb generation task was associated with significant decreases in beta oscillatory power (13–30 Hz) in frontal and temporal lobes. The MEG data were compared with other available presurgical non-invasive data including cortical stimulation, neuropsychological and fMRI data on language lateralization where available. We found that the lateralization of MEG beta power reduction was concordant with language dominance determined by one or more different assessment methods (i.e. cortical stimulation mapping, neuropsychological, fMRI or post-operative data) in 89% of patients. Our data suggest that qualitative hemispheric differences in task-related changes of spectral power could offer a promising insight into the contribution of dominant and non-dominant hemispheres in language processing and may help to characterize the specialization and lateralization of language processes in children.

Insular Cortex Surgery for the Treatment of Refractory Epilepsy

Focal epilepsy originating from the insular cortex is rare. One reason is the small amount of cortical tissue compared with other lobes of the brain. However, the incidence of insular epilepsy might be underestimated because of diagnostic difficulties. The semiology and the surface EEG are often not meaningful or even misleading, and elaborated imaging might be necessary. The close connections of the insular cortex with other potentially epileptogenic areas, such as the temporal lobe or frontal/central cortex, is increasingly recognized as possible reason for failure of epilepsy surgery for temporal or extratemporal seizures. Therefore, some centers consider invasive EEG recording of the insular cortex not only in case of insular epilepsy but also in other focal epilepsies with nonconclusive results from the presurgical work-up. The surgical approach to and resection of insular cortex is challenging because of its deep location and proximity to highly eloquent brain structures. Over the last decades, technical adjuncts like navigation tools, electrophysiological monitoring and intraoperative imaging have improved the outcome after surgery. Nevertheless, there is still a considerable rate of postoperative transient or permanent deficits, in some cases as unavoidable and calculated deficits. In most of the recent series, seizure outcome was favorable and comparable with extratemporal epilepsy surgery or even better. Up to now, the data volume concerning long-term follow-up is limited. This review focusses on the surgical challenges of resections to treat insular epilepsy, on prognostic factors concerning seizure outcome, on postoperative deficits and complications. Moreover, less invasive surgical techniques to treat epilepsy in this highly eloquent area are summarized.

Assessment of grammar optimizes language tasks for the intracarotid amobarbital procedure

PURPOSE

A previous study showed that assessment of language laterality could be improved by adding grammar tests to the recovery phase of the intracarotid amobarbital procedure (IAP) (Połczyńska et al. 2014). The aim of this study was to further investigate the extent to which grammar tests lateralize language function during the recovery phase of the IAP in a larger patient sample.

METHODS

Forty patients with drug-resistant epilepsy (14 females, thirty-two right-handed, mean age 38.5years, SD=10.6) participated in this study. On EEG, 24 patients had seizures originating in the left hemisphere (LH), 13 in the right hemisphere (RH), and 4 demonstrated mixed seizure origin. Thirty participants (75%) had bilateral injections, and ten (25%) had unilateral injections (five RH and five LH). Based on results from the encoding phase, we segregated our study participants to a LH language dominant and a mixed dominance group. In the recovery phase of the IAP, the participants were administered a new grammar test (the CYCLE-N) and a standard language test. We analyzed the laterality index measure and effect sizes in the two tests.

KEY FINDINGS

In the LH-dominant group, the CYCLE-N generated more profound language deficits in the recovery phase than the standard after injection to either hemisphere (p<0.001). At the same time, the laterality index for the grammar tasks was still higher than for the standard tests. Critically, the CYCLE-N administered in the recovery phase was nearly as effective as the standard tests given during the encoding phase.

SIGNIFICANCE

The results may be significant for individuals with epilepsy undergoing IAP. The grammar tests may be a highly efficient measure for lateralizing language function in the recovery phase.

Partial resection of presurgical fMRI activation is associated with a postsurgical loss of language function after frontal lobe epilepsy surgery

We describe five patients with frontal lobe epilepsy who underwent electrocortical stimulation (ES) for language localization and language functional magnetic resonance imaging (fMRI) prior to epilepsy surgery. Six months after surgery, three patients suffered from a drop of verbal fluency. In all of them, frontal areas with presurgical language fMRI activity were resected. Our results suggest that resection in regions of areas with presurgical fMRI activation is not without risk for a postsurgical loss of function, even when ES results were negative for language function in these areas. Using fMRI activations might be specifically helpful to plan the resection when ES delivered inconclusive results.

Evaluation of the factors influencing brain language laterality in presurgical planning

Brain lesions cause functional deficits, and one treatment for this condition is lesion resection. In most cases, presurgical planning (PSP) and the information from laterality indices are necessary for maximum preservation of the critical functions after surgery. Language laterality index (LI) is reliably estimated using functional magnetic resonance imaging (fMRI); however, this measure is under the influence of some external factors. In this study, we investigated the influence of a number of factors on language LI, using data from 120 patients (mean age=35.65 (±13.4) years) who underwent fMRI for PSP. Using two proposed language tasks from our previous works, brain left hemisphere was showed to be dominant for the language function, although a higher LI was obtained using the "Word Generation" task, compared to the "Reverse Word Reading". In addition, decline of LIs with age, and lower LI when the lesion invaded brain language area were observed. Meanwhile, gender, lesion side (affected hemisphere), LI calculation strategy, and fMRI analysis Z-values did not statistically show any influences on the LIs. Although fMRI is widely used to estimate language LI, it is shown here that in order to present a reliable language LI and to correctly select the dominant hemisphere of the brain, the influence of external factors should be carefully considered.

Language system organization in a quadrilingual with a brain tumor: Implications for understanding of the language network

In pre-neurosurgery language mapping it is critical to identify language-specific regions in multilingual speakers. We conducted pre-operative functional magnetic resonance imaging, and intraoperative language mapping in the unique case of a highly proficient quadrilingual with a left frontal brain tumor who acquired her second language at age 5, and her third and fourth languages at 15. We found a predominantly different organization in each language with only a few areas shared by all 4 languages. Contrary to existing evidence, impairment across languages was not related to age of acquisition, amount of exposure, or language similarity. This case suggests that the functional structure of the language system may be highly idiosyncratic in multilingual individuals and supports detailed study in this group to inform neurocognitive models of language.

Role of the Wada test and functional magnetic resonance imaging in preoperative mapping of language and memory: two atypical cases

The Wada test is an invasive procedure used to determine cerebral memory and language dominance as well as risk of cognitive deficits following neurosurgery. However, the potential risks of Wada testing have led some to consider foregoing Wada testing in candidates for resective epilepsy surgery with right hemispheric seizure onset. We present two atypical cases in which the Wada test showed unexpected memory and language lateralization. These cases underscore the importance of functional magnetic resonance in which imaging and Wada examination in right-handed individuals even when the lesion would not suggest atypical language representation.

Usage of fMRI for pre-surgical planning in brain tumor and vascular lesion patients: task and statistical threshold effects on language lateralization

BACKGROUND AND PURPOSE

Functional magnetic resonance imaging (fMRI) is a non-invasive pre-surgical tool used to assess localization and lateralization of language function in brain tumor and vascular lesion patients in order to guide neurosurgeons as they devise a surgical approach to treat these lesions. We investigated the effect of varying the statistical thresholds as well as the type of language tasks on functional activation patterns and language lateralization. We hypothesized that language lateralization indices (LIs) would be threshold- and task-dependent.

MATERIALS AND METHODS

Imaging data were collected from brain tumor patients (n = 67, average age 48 years) and vascular lesion patients (n = 25, average age 43 years) who received pre-operative fMRI scanning. Both patient groups performed expressive (antonym and/or letter-word generation) and receptive (tumor patients performed text-reading; vascular lesion patients performed text-listening) language tasks. A control group (n = 25, average age 45 years) performed the letter-word generation task.

RESULTS

Brain tumor patients showed left-lateralization during the antonym-word generation and text-reading tasks at high threshold values and bilateral activation during the letter-word generation task, irrespective of the threshold values. Vascular lesion patients showed left-lateralization during the antonym and letter-word generation, and text-listening tasks at high threshold values.

CONCLUSION

Our results suggest that the type of task and the applied statistical threshold influence LI and that the threshold effects on LI may be task-specific. Thus identifying critical functional regions and computing LIs should be conducted on an individual subject basis, using a continuum of threshold values with different tasks to provide the most accurate information for surgical planning to minimize post-operative language deficits.

Presurgical language lateralization assessment by fMRI and dichotic listening of pediatric patients with intractable epilepsy

Objective

The aim of this study was to evaluate the clinical use of a method to assess hemispheric language dominance in pediatric candidates for epilepsy surgery. The method is designed for patients but has previously been evaluated with healthy children.

Methods

Nineteen patients, 8–18 years old, with intractable epilepsy and candidates for epilepsy surgery were assessed. The assessment consisted of two functional MRI protocols (fMRI) intended to target frontal and posterior language networks respectively, and a behavioral dichotic listening task (DL). Regional left/right indices for each fMRI task from the frontal, temporal and parietal lobe were calculated, and left/right indices of the DL task were calculated from responses of consonants and vowels, separately. A quantitative analysis of each patient's data set was done in two steps based on clearly specified criteria. First, fMRI data and DL data were analyzed separately to determine whether the result from each of these assessments were conclusive or not. Thereafter, the results from the individual assessments were combined to reach a final conclusion regarding hemispheric language dominance.

Results

For 14 of the 19 subjects (74%) a conclusion was reached about their hemispheric language dominance. Nine subjects had a left-sided and five subjects had a right-sided hemispheric dominance. In three cases (16%) DL provided critical data to reach a conclusive result.

Conclusions

The success rate of conclusive language lateralization assessments in this study is comparable to reported rates on similar challenged pediatric populations. The results are promising but data from more patients than in the present study will be required to conclude on the clinical applicability of the method.

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Language lateralization was assessed in 19 pediatric candidates for epilepsy surgery.

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The assessment involved fMRI and an independent behavioral measure; dichotic listening.

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A two step analysis was employed combining fMRI and dichotic listening data.

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For 74% of the subjects a conclusion was reached about hemispheric language dominance.

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The rate of conclusive assessments in this study is comparable to reported rates on similar challenged pediatric populations.

Applications of blood-oxygen-level-dependent functional magnetic resonance imaging and diffusion tensor imaging in epilepsy

The lifetime prevalence of epilepsy ranges from 2.7 to 12.4 per 1000 in Western countries. Around 30% of patients with epilepsy remain refractory to antiepileptic drugs and continue to have seizures. Noninvasive imaging techniques such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) have helped to better understand mechanisms of seizure generation and propagation, and to localize epileptic, eloquent, and cognitive networks. In this review, the clinical applications of fMRI and DTI are discussed, for mapping cognitive and epileptic networks and organization of white matter tracts in individuals with epilepsy.

Cerebellar language mapping and cerebral language dominance in pediatric epilepsy surgery patients

Objective

Children with epilepsy often have reorganization of language networks and abnormal brain anatomy, making determination of language lateralization difficult. We characterized the proportion and distribution of language task activation in the cerebellum to determine the relationship to cerebral language lateralization.

Methods

Forty-six pediatric epilepsy surgery candidates (aged 7–19 years) completed an fMRI auditory semantic decision language task. Distribution of activated voxels and language laterality indices were computed using: (a) Broca's and Wernicke's areas and their right cerebral homologues; and (b) left and right cerebellar hemispheres. Language task activation was anatomically localized in the cerebellum.

Results

Lateralized language task activation in either cerebral hemisphere was highly correlated with lateralized language task activation in the contralateral cerebellar hemisphere (Broca vs. cerebellar: ρ = −0.54, p < 0.01). Cerebellar language activation was located within Crus I/II, areas previously implicated in non-motor functional networks.

Conclusions

Cerebellar language activation occurs in homologous regions of Crus I/II contralateral to cerebral language activation in patients with both right and left cerebral language dominance. Cerebellar language laterality could contribute to comprehensive pre-operative evaluation of language lateralization in pediatric epilepsy surgery patients. Our data suggest that patients with atypical cerebellar language activation are at risk for having atypical cerebral language organization.

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We examine fMRI cerebellar language activation in pediatric epilepsy surgery patients.

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A semantic decision task is employed to lateralize cerebral and cerebellar language.

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Cerebral and contralateral cerebellar language activations are highly correlated.

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Cerebellar language activation is located in right or left Crus I/II.

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Cerebellar language laterality may aid pre-operative cerebral language localization.

Deviation of the fully protracted tongue: is it a reliable indicator for language cerebral dominance?

Since its introduction in 1960, The Wada test has been considered the gold standard for language lateralization prior to ablative brain surgery. Due to the invasive nature of The Wada test several non-invasive techniques have been alternatively adopted. Recently, it has been suggested that the tongue deviates toward the language dominant cerebral hemisphere on full protraction. This suggestion is based on the important role the tongue plays in articulation and on the close anatomical relationship between the cortical tongue motor area and the motor speech area. It was proposed that this phenomenon could serve as a reliable and simple method for language brain lateralization. However, this hypothesis is still open for verification. In an attempt to correlate tongue deviation and language cerebral dominance we present and discuss in this paper the results of a study conducted on 339 free adult Jordanian volunteers. Tongue deviation and handedness were determined and statistically correlated. Our results showed that 62% of test subjects did not show any tongue deviation on full protrusion. Additionally, 9% of test subjects showed left-sided tongue deviation on full protraction in spite of 90% right handedness with presumed left language dominant cerebral hemisphere. We conclude that, at least in Jordanians, tongue deviation cannot be considered as a reliable indicator for language lateralization.

Same day tri-modality functional brain mapping prior to resection of a lesion involving eloquent cortex: technical feasibility

Non-invasive functional evaluation of the brain complements structural MRI imaging and has largely supplanted invasive techniques such as awake craniotomy. Techniques used for functional mapping of the brain include BOLD-functional MRI (fMRI), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS). We describe the case of a right-handed patient with a lesion centered in the left inferior perirolandic cortex who underwent fMRI, MEG, and TMS on a single day to facilitate maximal lesion resection while preserving eloquent cortex and eloquent white matter tracts.

Language dominance in children with epilepsy: concordance of fMRI with intracarotid amytal testing and cortical stimulation

Accurate localization of language function is critical in children undergoing epilepsy surgery. Functional magnetic resonance imaging (fMRI) is a noninvasive mapping method that has begun to replace electrocortical stimulation mapping (ESM) and the intracarotid amytal test (IAT). We used both quantitative and qualitative methods to evaluate the concordance of fMRI with ESM and IAT in 20 children using a panel of language tasks. In no cases did fMRI assessment of language hemisphere dominance identify the opposite hemisphere from assessment by IAT or ESM. Concordance with IAT and ESM was higher using fMRI visual inspection than an fMRI laterality index, which failed to lateralize language in a number of the subjects. We have demonstrated that fMRI has good concordance with more traditional methods of language mapping. When fMRI demonstrates bilateral language activations, however, we continue to recommend confirmatory testing by either IAT or ESM prior to resection in classic language regions.

Magnetoencephalography: fundamentals and established and emerging clinical applications in radiology

Magnetoencephalography is a noninvasive, fast, and patient friendly technique for recording brain activity. It is increasingly available and is regarded as one of the most modern imaging tools available to radiologists. The dominant clinical use of this technology currently centers on two, partly overlapping areas, namely, localizing the regions from which epileptic seizures originate, and identifying regions of normal brain function in patients preparing to undergo brain surgery. As a consequence, many radiologists may not yet be familiar with this technique. This review provides an introduction to magnetoencephalography, discusses relevant analytical techniques, and presents recent developments in established and emerging clinical applications such as pervasive developmental disorders. Although the role of magnetoencephalography in diagnosis, prognosis, and patient treatment is still limited, it is argued that this technology is exquisitely capable of contributing indispensable information about brain dynamics not easily obtained with other modalities. This, it is believed, will make this technology an important clinical tool for a wide range of disorders in the future.

Classification of fMRI patterns--a study of the language network segregation in pediatric localization related epilepsy

This article describes a pattern classification algorithm for pediatric epilepsy using fMRI language-related activation maps. 122 fMRI datasets from a control group (64) and localization related epilepsy patients (58) provided by five children's hospitals were used. Each subject performed an auditory description decision task. Using the artificial data as training data, incremental Principal Component Analysis was used in order to generate the feature space while overcoming memory requirements of large datasets. The nearest-neighbor classifier (NNC) and the distance-based fuzzy classifier (DFC) were used to perform group separation into left dominant, right dominant, bilateral, and others. The results show no effect of age, age at seizure onset, seizure duration, or seizure etiology on group separation. Two sets of parameters were significant for group separation, the patient vs. control populations and handedness. Of the 122 real datasets, 90 subjects gave the same classification results across all the methods (three raters, LI, bootstrap LI, NNC, and DFC). For the remaining datasets, 18 cases for the IPCA-NNC and 21 cases for the IPCA-DFC agreed with the majority of the five classification results (three visual ratings and two LI results). Kappa values vary from 0.59 to 0.73 for NNC and 0.61 to 0.75 for DFC, which indicate good agreement between NNC or DFC with traditional methods. The proposed method as designed can serve as an alternative method to corroborate existing LI and visual rating classification methods and to resolve some of the cases near the boundaries in between categories.

Language lateralization in children aged 10 to 11 years: a combined fMRI and dichotic listening study

Objective

The aims of this study were to develop and assess a method to map language networks in children with two auditory fMRI protocols in combination with a dichotic listening task (DL). The method is intended for pediatric patients prior to epilepsy surgery. To evaluate the potential clinical usefulness of the method we first wanted to assess data from a group of healthy children.

Methods

In a first step language test materials were developed, intended for subsequent implementation in fMRI protocols. An evaluation of this material was done in 30 children with typical development, 10 from the 1^st, 4^th and the 7^th grade, respectively. The language test material was then adapted and implemented in two fMRI protocols intended to target frontal and posterior language networks. In a second step language lateralization was assessed in 17 typical 10–11 year olds with fMRI and DL. To reach a conclusion about language lateralization, firstly, quantitative analyses of the index data from the two fMRI tasks and the index data from the DL task were done separately. In a second step a set of criteria were applied to these results to reach a conclusion about language lateralization. The steps of these analyses are described in detail.

Results

The behavioral assessment of the language test material showed that it was well suited for typical children. The results of the language lateralization assessments, based on fMRI data and DL data, showed that for 15 of the 17 subjects (88%) a conclusion could be reached about hemispheric language dominance. In 2 cases (12%) DL provided critical data.

Conclusions

The employment of DL combined with language mapping using fMRI for assessing hemispheric language dominance is novel and it was deemed valuable since it provided additional information compared to the results gained from each method individually.

Clinical language fMRI with real-time monitoring in temporal lobe epilepsy: online processing methods

The increasing demand for clinical fMRI data has resulted in a need to translate research methods to clinical use. Referrals for language lateralization prior to epilepsy surgery are becoming more common, but time constraints make this unachievable in many busy neuroimaging departments. This study examines whether a single covert verbal fluency paradigm with real-time monitoring and online processing (BrainWave) could replace conventional offline processing (SPM) for the purpose of establishing expressive language dominance prior to epilepsy surgery. We analyzed language fMRI results of 30 patients (17 female; 24 right-handed; median age: 30.5) with temporal lobe epilepsy. Concordance between visual assessment of SPM and BrainWave was 92.8%. Lateralization indices correlated closely with visual assessments of lateralization with a concordance of 85.7%. BrainWave provided a real-time, fast and accurate display of language lateralization easily applied in a clinical setting using only online image processing.

Dynamics of hemispheric dominance for language assessed by magnetoencephalographic imaging

OBJECTIVE

The goal of the current study was to examine the dynamics of language lateralization using magnetoencephalographic (MEG) imaging, to determine the sensitivity and specificity of MEG imaging, and to determine whether MEG imaging can become a viable alternative to the intracarotid amobarbital procedure (IAP), the current gold standard for preoperative language lateralization in neurosurgical candidates.

METHODS

MEG was recorded during an auditory verb generation task and imaging analysis of oscillatory activity was initially performed in 21 subjects with epilepsy, brain tumor, or arteriovenous malformation who had undergone IAP and MEG. Time windows and brain regions of interest that best discriminated between IAP-determined left or right dominance for language were identified. Parameters derived in the retrospective analysis were applied to a prospective cohort of 14 patients and healthy controls.

RESULTS

Power decreases in the beta frequency band were consistently observed following auditory stimulation in inferior frontal, superior temporal, and parietal cortices; similar power decreases were also seen in inferior frontal cortex prior to and during overt verb generation. Language lateralization was clearly observed to be a dynamic process that is bilateral for several hundred milliseconds during periods of auditory perception and overt speech production. Correlation with the IAP was seen in 13 of 14 (93%) prospective patients, with the test demonstrating a sensitivity of 100% and specificity of 92%.

INTERPRETATION

Our results demonstrate excellent correlation between MEG imaging findings and the IAP for language lateralization, and provide new insights into the spatiotemporal dynamics of cortical speech processing.

Cerebral blood flow and fMRI BOLD auditory language activation in temporal lobe epilepsy

PURPOSE

Blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI), an important research and clinical tool, depends on relatively greater transient increases in (regional cerebral blood flow) rCBF than cerebral metabolic rate for oxygen during neural activity. We investigated whether reduced resting rCBF in patients with temporal lobe epilepsy affects BOLD signal during fMRI language mapping.

METHODS

We used [(15)O] water positron emission tomography (PET) to measure rCBF, and 3 Tesla echo planar imaging (EPI) BOLD fMRI with an auditory description decision task in 33 patients with temporal lobe epilepsy (16 men; mean age 33.6 ± standard deviation [SD] 10.6 years; epilepsy onset 14.8 ± 10.6 years; mean duration 18.8 ± 13.2 years; 23 left focus, 10 right focus). Anatomic regions drawn on structural MRI, based on the Wake Forest Pick Atlas, included Wernicke's area (WA), inferior frontal gyrus (IFG), middle frontal gyrus (MFG), and hippocampus (HC). Laterality indices (LIs), and asymmetry indices (AIs), were calculated on coregistered fMRI and PET.

KEY FINDINGS

Twelve patients had mesial temporal sclerosis (seven on the left), two patients had a tumor or malformation of cortical development (both left), one patient a right temporal cyst, and 18 patients had normal MRI (14 left). Decreasing relative left WA CBF correlated with decreased left IFG voxel activation and decreasing left IFG LI. However, CBF WA AI was not related to left WA voxel activation itself or WA LI. There was a weak positive correlation between absolute CBF and fMRI activation in left IFG, right IFG, and left WA. Patients with normal and abnormal MRI did not differ in fMRI activation or rCBF AIs.

SIGNIFICANCE

Reduced WA rCBF is associated with reduced fMRI activation in IFG but not WA itself, suggesting distributed network effects, but not impairment of underlying BOLD response. Hypoperfusion in TLE does not affect fMRI clinical value.

From research to clinical practice: implementation of functional magnetic imaging and white matter tractography in the clinical environment

In the last two decades functional magnetic resonance imaging (fMRI) has dominated research in neuroscience. However, only recently has it taken the first steps in translation to the clinical field. In this paper we describe the advantages of fMRI and DTI and the possible benefits of implementing these methods in clinical practice. We review the current clinical usages of fMRI and DTI and discuss the challenges and difficulties of translating these methods to clinical use. The most common application today is in neurosurgery. fMRI and DTI are done preoperatively for brain tumor patients who are having tumors removed and for epilepsy patients who are candidates for temporal resection. Imaging results supply the neurosurgeon with essential information regarding possible functional damage and thereby aid both in planning and performing surgery. Scientific research suggests more promising potential implementations of fMRI and DTI in improving diagnosis and rehabilitation. These advanced imaging methods can be used for pre-symptomatic diagnosis, as a differentiating biomarker in the absence of anatomical measurements, and for identification of mental response in the absence of motor-sensory abilities. These methods can aid and direct rehabilitation by predicting the success of possible interventions and rehabilitation options and by supplying a measure for biofeedback. This review opens a window to the state of the art neuroimaging methods being implemented these days into the clinical practice and provides a glance to the future clinical possibilities of fMRI and DTI.

Wada you do for language: fMRI and language lateralization?

Language Lateralization in Epilepsy Patients: fMRI Validated with the Wada Procedure. Arora J, Pugh K, Westerveld M, Spencer S, Spencer DD, Todd Constable R. Epilepsia 2009;50(10):2225–2241.

Purpose

This work examines the efficacy of functional magnetic resonance imaging (fMRI) for language lateralization using a comprehensive three-task language-mapping approach. Two localization methods and four different metrics for quantifying activation within hemisphere are compared and validated with Wada testing. Sources of discordance between fMRI and Wada lateralization are discussed with respect to specific patient examples.

Methods

fMRI language mapping was performed in patients with epilepsy ( N = 40) using reading sentence comprehension, auditory sentence comprehension, and a verbal fluency task. This was compared with the Wada procedure using both whole-brain and midline exclusion-based analyses. Different laterality scores were examined as a function of statistical threshold to investigate the sensitivity to threshold effects.

Results

For the lateralized patients categorized by Wada, fMRI laterality indices were concordant with the Wada procedure results in 83.87% patients for the reading task, 83.33% patients for the auditory task, 76.92% patients for the verbal fluency task, and in 91.3% patients for the conjunction analysis. The patients categorized as bilateral via the Wada procedure showed some hemispheric dominance in fMRI, and discrepancies between the Wada test findings and the functional laterality scores arose for a range of reasons.

Discussion

Discordance was dependent upon whether whole-brain or midline exclusion method-based lateralization was calculated, and in the former case the inclusion of the occipital and other midline regions often negatively influenced the lateralization scores. Overall fMRI was in agreement with the Wada test in 91.3% of patients, suggesting its utility for clinical use with the proper consideration given to the confounds discussed in this work. Cerebral Lesions Can Impair fMRI-Based Language Lateralization. Wellmer J, Weber B, Urbach H, Reul J, Fernandez G, Elger CE. Epilepsia 2009;50(10):2213–2224.

Purpose

Several small patient studies and case reports raise concerns that the reliability of functional magnetic resonance imaging (fMRI) may be impaired in the vicinity of cerebral lesions. This could affect the clinical validity of fMRI for presurgical language lateralization. The current study sets out to identify if a systematic effect of lesion type and localization on fMRI exists.

Methods

We classify lesions typically occurring in epilepsy patients according to 1) their potential to disturb blood oxygenation level-dependent—effect generation or detection or to disturb spatial brain normalization, and 2) the proximity of lesions to protocol-specific volumes of interest (VOIs). The effect of lesions is evaluated through the examination of 238 epilepsy patients and a subgroup of 37 patients with suspected unilateral left-language dominance according to the Wada test.

Results

Patients with fMRI-critical lesions such as cavernomas, gliomas, and mass defects close to VOIs, or with severe atrophy, show lower lateralization indices and more often discordant language lateralization with the Wada test than do patients without such lesions.

Discussion

This study points seriously toward fMRI-language lateralization being sensitive to cerebral lesions. Some lesion types and locations are more critical than others. Our results question the noncritical application of fMRI in patients with cerebral lesions.

fMRI language dominance and FDG-PET hypometabolism

BACKGROUND

Atypical language dominance is common in patients with temporal lobe epilepsy. We examined the association of left temporal hypometabolism with laterality of fMRI activation in a language task in a cross-sectional study.

METHODS

Thirty patients with temporal lobe epilepsy (mean age 32.4 ± 11.0 years [range 18-55]; epilepsy onset 15.3 ± 11.3 years [range 0.8-40]; 22 left focus, 8 right focus) had (18)fluoro-deoxyglucose (FDG)-PET using noninvasive cardiac input function. After MRI-based partial volume correction, regional glucose metabolism (CMRglc) was measured and asymmetry index, AI = 2(l - R)/(L + R), calculated. fMRI language dominance was assessed with an auditory definition decision paradigm at 3 T. fMRI data were analyzed in SPM2 using regions of interest from Wake Forest PickAtlas (Wernicke area [WA], inferior frontal gyrus [IFG], middle frontal gyrus [MFG]) and bootstrap laterality index, LI = (l - R/L + R).

RESULTS

Nineteen patients had ipsilateral temporal hypometabolism; 3 of 4 patients with atypical language had abnormal FDG-PET. Increasing left midtemporal hypometabolism correlated with decreased MFG LI (r = -0.41, p < 0.05) and showed trends with WA LI (r = -0.37, p = 0.055) and IFG LI (r = -0.31, p = 0.099); these relationships became more significant after controlling for age at onset. Increasing hypometabolism was associated with fewer activated voxels in WA ipsilateral to the focus and more activated voxels contralaterally, but overall, activation amount in left WA was similar to subjects without left temporal hypometabolism (t = -1.39, p > 0.10).

CONCLUSIONS

We did not find evidence of impaired blood oxygenation level-dependent response in hypometabolic cortex. Regional hypometabolism appears to be a marker for the temporal lobe dysfunction that leads to displacement of language function.

Imaging in the surgical treatment of epilepsy

Medically refractory focal epilepsy is potentially curable by surgery. This Review considers the application of recent advances in structural and functional brain imaging to increase the number of patients with epilepsy who are treated surgically, and to reduce the risk of complications arising from such intervention. Current optimal MRI of brain structure can identify previously undetectable lesions, with voxel-based and quantitative analyses further increasing the diagnostic yield. If MRI proves unremarkable, PET (with (18)F-fluorodeoxyglucose) and single-photon emission CT of ictal-interictal cerebral blood flow might identify the brain region that contains the epileptic focus. Magnetoencephalography plus simultaneous EEG and functional MRI can map the location of interictal epileptic discharges, thereby facilitating placement of intracranial recording electrodes to define the site of seizure onset. Functional MRI can also lateralize language and localize primary motor, somatosensory and language areas, and shows promise for predicting the effects of temporal lobe resection on memory. Tractography can visualize the main cerebral white matter tracts, thereby predicting and reducing surgery risk. Currently, displays of the optic radiation and pyramidal tracts are the most relevant for epilepsy surgery. Reliable integration of structural and functional data into surgical image-guidance systems is being pursued, and promises safer neurosurgery for epilepsy in the future.

Regional and hemispheric determinants of language laterality: implications for preoperative fMRI

Language is typically a function of the left hemisphere but the right hemisphere is also essential in some healthy individuals and patients. This inter-subject variability necessitates the localization of language function, at the individual level, prior to neurosurgical intervention. Such assessments are typically made by comparing left and right hemisphere language function to determine "language lateralization" using clinical tests or fMRI. Here, we show that language function needs to be assessed at the region and hemisphere specific level, because laterality measures can be misleading. Using fMRI data from 82 healthy participants, we investigated the degree to which activation for a semantic word matching task was lateralized in 50 different brain regions and across the entire cortex. This revealed two novel findings. First, the degree to which language is lateralized across brain regions and between subjects was primarily driven by differences in right hemisphere activation rather than differences in left hemisphere activation. Second, we found that healthy subjects who have relatively high left lateralization in the angular gyrus also have relatively low left lateralization in the ventral precentral gyrus. These findings illustrate spatial heterogeneity in language lateralization that is lost when global laterality measures are considered. It is likely that the complex spatial variability we observed in healthy controls is more exaggerated in patients with brain damage. We therefore highlight the importance of investigating within hemisphere regional variations in fMRI activation, prior to neuro-surgical intervention, to determine how each hemisphere and each region contributes to language processing.

fMRI assessment of language lateralization: an objective approach

Language lateralization based on functional magnetic resonance imaging (fMRI) is often used in clinical neurological settings. Currently, interpretation of the distribution, pattern and extent of language activation can be heavily dependent on the chosen statistical threshold. The aim of the present study was to 1) test the robustness of adaptive thresholding of fMRI data to yield a fixed number of active voxels, and to 2) develop a largely threshold-independent method of assessing when individual patients have statistically atypical language lateralization. Simulated data and real fMRI data in 34 healthy controls and 4 selected epilepsy patients performing a verbal fluency language fMRI task were used. Dependence of laterality on the thresholding method is demonstrated for simulated and real data. Simulated data were used to test the hypothesis that thresholding based upon a fixed number of active voxels would yield a laterality index that was more stable across a range of signal strengths (study power) compared to thresholding at a fixed p value. This stability allowed development of a method comparing an individual to a group of controls across a wide range of thresholds, providing a robust indication of atypical lateralization that is more objective than conventional methods. Thirty healthy controls were used as normative data for the threshold-independent method, and the remaining subjects were used as illustrative examples. The method could also be used more generally to assess relative regional distribution of activity in other neuroimaging paradigms (for example, one could apply it to the assessment of lateralization of activation in a memory task, or to the assessment of anterior-posterior distribution rather than laterality).