A reconsideration of bilateral language representation based on the intracarotid amobarbital procedure

Recovery from aphasia in the first year after stroke

Most individuals who experience aphasia after a stroke recover to some extent, with the majority of gains taking place in the first year. The nature and time course of this recovery process is only partially understood, especially its dependence on lesion location and extent, which are the most important determinants of outcome. The aim of this study was to provide a comprehensive description of patterns of recovery from aphasia in the first year after stroke. We recruited 334 patients with acute left hemisphere supratentorial ischaemic or haemorrhagic stroke and evaluated their speech and language function within 5 days using the Quick Aphasia Battery (QAB). At this initial time point, 218 patients presented with aphasia. Individuals with aphasia were followed longitudinally, with follow-up evaluations of speech and language at 1 month, 3 months, and 1 year post-stroke, wherever possible. Lesions were manually delineated based on acute clinical MRI or CT imaging. Patients with and without aphasia were divided into 13 groups of individuals with similar, commonly occurring patterns of brain damage. Trajectories of recovery were then investigated as a function of group (i.e. lesion location and extent) and speech/language domain (overall language function, word comprehension, sentence comprehension, word finding, grammatical construction, phonological encoding, speech motor programming, speech motor execution, and reading). We found that aphasia is dynamic, multidimensional, and gradated, with little explanatory role for aphasia subtypes or binary concepts such as fluency. Patients with circumscribed frontal lesions recovered well, consistent with some previous observations. More surprisingly, most patients with larger frontal lesions extending into the parietal or temporal lobes also recovered well, as did patients with relatively circumscribed temporal, temporoparietal, or parietal lesions. Persistent moderate or severe deficits were common only in patients with extensive damage throughout the middle cerebral artery distribution or extensive temporoparietal damage. There were striking differences between speech/language domains in their rates of recovery and relationships to overall language function, suggesting that specific domains differ in the extent to which they are redundantly represented throughout the language network, as opposed to depending on specialized cortical substrates. Our findings have an immediate clinical application in that they will enable clinicians to estimate the likely course of recovery for individual patients, as well as the uncertainty of these predictions, based on acutely observable neurological factors.

Time course of right-hemisphere recruitment during word production following left-hemisphere damage: A single case of young stroke

Our understanding of post-stroke language function is largely based on older age groups, who show increasing age-related brain pathology and neural reorganisation. To illustrate language outcomes in the young-adult brain, we present the case of J., a 23-year-old woman with chronic aphasia from a left-hemisphere stroke affecting the temporal lobe. Diffusion MRI-based tractography indicated that J.'s language-relevant white-matter structures were severely damaged. Employing magnetoencephalography (MEG), we explored J.'s conceptual preparation and word planning abilities using context-driven and bare picture-naming tasks. These revealed naming deficits, manifesting as word-finding difficulties and semantic paraphasias about half of the time. Naming was however facilitated by semantically constraining lead-in sentences. Altogether, this pattern indicates disrupted lexical-semantic and phonological retrieval abilities. MEG revealed that J.'s conceptual and naming-related neural responses were supported by the right hemisphere, compared to the typical left-lateralised brain response of a matched control. Differential recruitment of right-hemisphere structures (330-440 ms post-picture onset) was found concurrently during successful naming (right mid-to-posterior temporal lobe) and word-finding attempts (right inferior frontal gyrus). Disconnection of the temporal lobes via corpus callosum was not critical for recruitment of the right hemisphere in visually guided naming, possibly due to neural activity right lateralising from the outset. Although J.'s right hemisphere responded in a timely manner during word planning, its lexical and phonological retrieval abilities remained modest.

Impact of development and recent-onset epilepsy on language dominance

OBJECTIVE

Reorganization of the language network from typically left-lateralized frontotemporal regions to bilaterally distributed or right-lateralized networks occurs in anywhere from 25%-30% of patients with focal epilepsy. In patients who have been recently diagnosed with epilepsy, an important question remains as to whether it is the presence of seizures or the underlying epilepsy etiology that leads to atypical language representations. This question becomes even more interesting in pediatric samples, where the typical developmental processes of the language network may confer more variability and plasticity in the language network. We assessed a carefully selected cohort of children with recent-onset epilepsy to examine whether it is the effects of seizures or their underlying cause that leads to atypical language lateralization.

METHODS

We used functional magnetic resonance imaging (fMRI) to compare language laterality in children with recently diagnosed focal unaware epilepsy and age-matched controls. Age at epilepsy onset (age 4 to 6 years vs age 7 to 12 years) was also examined to determine if age at onset influenced laterality.

RESULTS

The majority of recent-onset patients and controls exhibited left-lateralized language. There was a significant interaction such that the relationship between epilepsy duration and laterality differed by age at onset. In children with onset after age 6, a longer duration of epilepsy was associated with less left-lateralized language dominance. In contrast, in children with onset between 4 and 6 years of age, a longer duration of epilepsy was not associated with less left language dominance.

SIGNIFICANCE

Our results demonstrate that although language remained largely left-lateralized in children recently diagnosed with epilepsy, the impact of seizure duration depended on age at onset, indicating that the timing of developmental and disease factors are important in determining language dominance.

Cerebral Polymorphisms for Lateralisation: Modelling the Genetic and Phenotypic Architectures of Multiple Functional Modules

Recent fMRI and fTCD studies have found that functional modules for aspects of language, praxis, and visuo-spatial functioning, while typically left, left and right hemispheric respectively, frequently show atypical lateralisation. Studies with increasing numbers of modules and participants are finding increasing numbers of module combinations, which here are termed cerebral polymorphisms—qualitatively different lateral organisations of cognitive functions. Polymorphisms are more frequent in left-handers than right-handers, but it is far from the case that right-handers all show the lateral organisation of modules described in introductory textbooks. In computational terms, this paper extends the original, monogenic McManus DC (dextral-chance) model of handedness and language dominance to multiple functional modules, and to a polygenic DC model compatible with the molecular genetics of handedness, and with the biology of visceral asymmetries found in primary ciliary dyskinesia. Distributions of cerebral polymorphisms are calculated for families and twins, and consequences and implications of cerebral polymorphisms are explored for explaining aphasia due to cerebral damage, as well as possible talents and deficits arising from atypical inter- and intra-hemispheric modular connections. The model is set in the broader context of the testing of psychological theories, of issues of laterality measurement, of mutation-selection balance, and the evolution of brain and visceral asymmetries.

Clinical Speech fMRI in Children and Adolescents : Development of an Optimal Protocol and Analysis Algorithm

Purpose

In patients with drug-resistant focal epilepsy, surgical resection is often the only treatment option to achieve long-term seizure control. Prior to brain surgery involving potential language areas, identification of hemispheric language dominance is crucial. Our group developed and validated a functional magnetic resonance imaging (fMRI) battery of four pediatric language tasks. The present study aimed at optimizing fMRI data acquisition and analysis using these tasks.

Methods

We retrospectively analyzed speech fMRI examinations of 114 neuropediatric patients (age range 5.8–17.8 years) who were examined prior to possible epilepsy surgery. In order to evaluate hemispheric language dominance, 1–4 language tasks (vowel identification task VIT, word-chain task WCT, beep-story task BST, synonym task SYT) were measured.

Results

Language dominance was classified using fMRI activation in the 13 validly lateralizing ROIs (VLR) in frontal, temporal and parietal lobes and cerebellum of the recent validation study from our group: 47/114 patients were classified as left-dominant, 34/114 as bilateral and 6/114 as right-dominant. In an attempt to enlarge the set of VLR, we then compared for each task agreement of these ROI activations with the classified language dominance. We found four additional task-specific ROIs showing concordant activation and activation in ≥ 10 sessions, which we termed validly lateralizing (VLR_new). The new VLRs were: for VIT the temporal language area and for SYT the middle frontal gyrus, the intraparietal sulcus and cerebellum. Finally, in order to find the optimal sequence of measuring the different tasks, we analyzed the success rates of single tasks and all possible task combinations. The sequence 1) VIT 2) WCT 3) BST 4) SYT was identified as the optimal sequence, yielding the highest chance to obtain reliable results even when the fMRI examination has to be stopped, e.g., due to lack of cooperation.

Conclusion

Our suggested task order together with the enlarged set of VLR_new may contribute to optimize pediatric speech fMRI in a clinical setting.

Supplementary Information

The online version of this article (10.1007/s00062-021-01097-z) contains supplementary material, which is available to authorized users.

Beyond the Wada: An updated approach to pre-surgical language and memory testing: An updated review of available evaluation techniques and recommended workflow to limit Wada test use to essential clinical cases

The Intracarotid amobarbital test (IAT), also called Wada test, is considered the "gold standard" for lateralizing language dominance in the pre-surgical evaluation of patients with epilepsy. In addition, it has been further modified to assess the postoperative risk of amnesia in patients undergoing temporal lobectomy. Since then it has been utilized to lateralize language and assess pre-surgical memory function. Over the years, its popularity has declined due to several limitations and availability of alternative procedures like fMRI and MEG. A survey of its use in the pre-surgical evaluation for epilepsy surgery has not been performed since the 2008 international survey by Baxendale et al. and it was heavily skewed due to data from European and North American countries. Only approximately 12% of the epilepsy centers indicated that they used the Wada test in every patient to assess preoperative memory function and language lateralization before temporal lobectomy. Nowadays, we have many functional mapping tools at our disposal. It has become somewhat unsuitable to have epilepsy patients undergo an invasive test such as the Wada test for the risks associated with it outweigh the benefits. Our objective is to review the Wada Test and alternative methods of assessing language and memory dominance, as it is past its prime and should only be used in specific circumstances.

Unexpected absence of aphasia following left temporal hemorrhage: a case study with functional neuroimaging to characterize the nature of atypical language localization

Unexpected absence of aphasia after left-hemisphere perisylvian damage is often assumed to reflect right-hemisphere language lateralization, but other potential explanations include bilateral language representation, or sparing of critical left-hemisphere regions due to individual variability. We describe the case of a left-handed gentleman who presented with no aphasia after a left temporal hemorrhage. We used functional neuroimaging to determine how his language network had been spared. In this case, we observed unequivocal right-hemisphere lateralization of language function, explaining his lack of aphasia. We discuss the variability of language organization and highlight outstanding questions about the implications of damage in different scenarios.

Hemispheric asymmetries in processing numerical meaning in arithmetic

Hemispheric asymmetries in arithmetic have been hypothesized based on neuropsychological, developmental, and neuroimaging work. However, it has been challenging to separate asymmetries related to arithmetic specifically, from those associated general cognitive or linguistic processes. Here we attempt to experimentally isolate the processing of numerical meaning in arithmetic problems from language and memory retrieval by employing novel non-symbolic addition problems, where participants estimated the sum of two dot arrays and judged whether a probe dot array was the correct sum of the first two arrays. Furthermore, we experimentally manipulated which hemisphere receive the probe array first using a visual half-field paradigm while recording event-related potentials (ERP). We find that neural sensitivity to numerical meaning in arithmetic arises under left but not right visual field presentation during early and middle portions of the late positive complex (LPC, 400-800 ms). Furthermore, we find that subsequent accuracy for judgements of whether the probe is the correct sum is better under right visual field presentation than left, suggesting a left hemisphere advantage for integrating information for categorization or decision making related to arithmetic. Finally, neural signatures of operational momentum, or differential sensitivity to whether the probe was greater or less than the sum, occurred at a later portion of the LPC (800-1000 ms) and regardless of visual field of presentation, suggesting a temporal and functional dissociation between magnitude and ordinal processing in arithmetic. Together these results provide novel evidence for differences in timing and hemispheric lateralization for several cognitive processes involved in arithmetic thinking.

You may now kiss the bride: Interpretation of social situations by individuals with right or left hemisphere injury

While left hemisphere damage (LHD) has been clearly shown to cause a range of language impairments, patients with right hemisphere damage (RHD) also exhibit communication deficits, such as difficulties processing prosody, discourse, and social contexts. In the current study, individuals with RHD and LHD were directly compared on their ability to interpret what a character in a cartoon might be saying or thinking, in order to better understand the relative role of the right and left hemisphere in social communication. The cartoon stimuli were manipulated so as to elicit more or less formulaic responses (e.g., a scene of a couple being married by a priest vs. a scene of two people talking, respectively). Participants' responses were scored by blind raters on how appropriately they captured the gist of the social situation, as well as how formulaic and typical their responses were. Results showed that RHD individuals' responses were rated as significantly less appropriate than controls and were also significantly less typical than controls and individuals with LHD. Individuals with RHD produced a numerically lower proportion of formulaic expressions than controls, but this difference was only a trend. Counter to prediction, the pattern of performance across participant groups was not affected by how constrained/formulaic the social situation was. The current findings expand our understanding of the roles that the right and left hemispheres play in social processing and communication and have implications for the potential treatment of social communication deficits in individuals with RHD.

Variation in homotopic areas' activity and inter-hemispheric intrinsic connectivity with type of language lateralization: an FMRI study of covert sentence generation in 297 healthy volunteers

We investigated the regional correlates of differences in hemispheric lateralization in 297 healthy volunteers [including 153 left-handers (LH)] previously classified into three types of language lateralization according to their hemispheric functional lateralization index measured with fMRI during covert sentence production versus word list production (PRODSENT-LIST): 250 leftward asymmetrical Typicals, 10 rightward asymmetrical Strong-atypicals (only LH), and 37 Ambilaterals with weak lateralization. Using a functionally driven homotopic atlas (AICHA), we compared patterns of regional asymmetry during PRODSENT-LIST in these three groups. Among the 192 homotopic regions of interest (hROIs) of the AICHA atlas, 58 exhibited a significant effect of the type of lateralization on their BOLD signal variation during PRODSENT-LIST. The analyses of patterns of asymmetry of these 58 hROIs showed that (1) hROIs asymmetries in Strong-atypicals were significantly negatively correlated with those observed in Typicals, which indicates that their regional pattern of rightward asymmetries was comparable to the regional pattern of leftward language asymmetries of Typicals; (2) right- and left-handed Typicals had identical profiles, whereas left-handed Ambilaterals exhibited reduced leftward asymmetry as compared either to right-handed Ambilaterals or to Typicals. Moreover, left-handed Ambilaterals pattern of hROIs asymmetries significantly positively correlated with those of both Typicals and Strong-atypicals. In 291 of the participants, we tested the hypothesis that differences in language lateralization were associated with differences in inter-hemispheric connectivity during resting state by measuring their regional homotopic inter-hemispheric intrinsic connectivity coefficient (rHIICC) in 36 of the 58 hROIs known to be connected via the corpus callosum. Mean rHIICCs were negatively correlated with task-induced functional asymmetries, suggesting that enhanced inter-hemispheric cooperation at rest translates into increased inter-hemispheric cooperation during language production. In addition, the left-handed Ambilaterals exhibited a significantly larger rHIICC compared with right-handed Ambilaterals and Typicals, confirming a difference in inter-hemispheric organization in this group.

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Speech and language-related functions tend to depend on the left hemisphere more than the right in most right-handed (dextral) participants. This relationship is less clear in non-right handed (adextral) people, resulting in surprisingly polarized opinion on whether or not they are as lateralized as right handers. The present analysis investigates this issue by largely ignoring methodological differences between the different neuroscientific approaches to language lateralization, as well as discrepancies in how dextral and adextral participants were recruited or defined. Here we evaluate the tendency for dextrals to be more left hemisphere dominant than adextrals, using random effects meta analyses. In spite of several limitations, including sample size (in the adextrals in particular), missing details on proportions of groups who show directional effects in many experiments, and so on, the different paradigms all point to proportionally increased left hemispheric dominance in the dextrals. These results are analyzed in light of the theoretical importance of these subtle differences for understanding the cognitive neuroscience of language, as well as the unusual asymmetry in most adextrals.

Predictors of language lateralization in temporal lobe epilepsy

Among patients with epilepsy, atypical (rightward) language lateralization has been associated with left-handedness, a left seizure focus, an early age at seizure onset, and familial sinistrality, although these associations are not consistently observed. No study has examined all of these factors in relation to language lateralization in the same epilepsy sample, let alone in a sample comprised only of patients with temporal lobe epilepsy. Moreover, little consideration has been given in previous studies to how language lateralization might be influenced by the interplay between different factors, or how much unique variance in language lateralization is explained by each factor. The primary aim of this study was to examine the combined influences of handedness, side of seizure focus, age at seizure onset, and familial sinistrality on language lateralization in temporal lobe epilepsy patients. A secondary aim was to determine which factors uniquely contribute to the prediction of language lateralization. 162 patients with intractable temporal lobe epilepsy underwent functional MRI language mapping, from which language lateralization indexes were derived. Degree of handedness was measured via the Edinburgh Handedness Inventory. Main and 2-way interaction effects on language lateralization indexes were examined via linear regressions and Fisher exact tests. Significant effects were next examined in multiple regressions to identify unique predictors of language lateralization indexes. When examined in isolation in regressions, only left-handedness and a left seizure focus predicted atypical (rightward) language lateralization. These results, however, were qualified by interaction effects demonstrating that stronger left hand preference was associated with greater atypical language lateralization only among patients with a left seizure focus, an early or intermediate age at seizure onset, or no familial sinistrality. In follow-up multiple regressions, the interaction terms accounted for a significant amount of variance in language lateralization indexes above and beyond main effects. Additionally, side of seizure focus and its interaction with handedness uniquely predicted language lateralization indexes. Results indicate that degree of left-handedness is a marker of greater atypical (rightward) language lateralization in temporal lobe epilepsy but only in the context of seizure characteristics that have the potential to drive joint reorganization of language and hand preference (i.e., left seizure focus, or early or intermediate age at seizure onset) or in the absence of a genetic predisposition for left-handedness (i.e., no familial sinistrality). This study advances existing knowledge by illustrating how different factors combine to jointly affect language lateralization, and by identifying side of seizure focus and its interaction with handedness as unique predictors of language lateralization in temporal lobe epilepsy.

Sensitivity and specificity of Ankara University Cerebral Dominance Inventory in comparison with the Wada test

We aimed to examine the sensitivity and specificity of the Ankara University Cerebral Dominance Inventory (AUCDI) in determining left cerebral dominance compared with the Wada test. The AUCDI and Wada test were applied to 49 patients referred to Ankara University for epilepsy surgery. Hand, foot and 'total' preference scores were specified according to the results of the inventory. Thirty-eight of the patients had left cerebral dominance and 11 had atypical cerebral dominance for language. 86 % of the patients were right-handed and 43 % were right-footed. When compared with the results of the Wada test, the sensitivity of the AUCDI for each 'total preference', and hand and foot preference was 90, 95 and 50 % and specificity was 46, 46 and 82 %, respectively. The percentage of right-footed patients was low when compared with the other studies. This difference might result from the method used for assessing foot preference by the actual demonstration of the task rather than just asking about the performance. The AUCDI was found to be sensitive in terms of 'total preference' and hand preference, and specific in terms of foot preference for determining the left hemisphere dominance in patients preferring the right side. It was a cheap and noninvasive alternative to the Wada test, appropriate for clinical bedside evaluation.

Characterization of atypical language activation patterns in focal epilepsy

OBJECTIVE

Functional magnetic resonance imaging is sensitive to the variation in language network patterns. Large populations are needed to rigorously assess atypical patterns, which, even in neurological populations, are a minority.

METHODS

We studied 220 patients with focal epilepsy and 118 healthy volunteers who performed an auditory description decision task. We compared a data-driven hierarchical clustering approach to the commonly used a priori laterality index (LI) threshold (LI < 0.20 as atypical) to classify language patterns within frontal and temporal regions of interest. We explored (n = 128) whether IQ varied with different language activation patterns.

RESULTS

The rate of atypical language among healthy volunteers (2.5%) and patients (24.5%) agreed with previous studies; however, we found 6 patterns of atypical language: a symmetrically bilateral, 2 unilaterally crossed, and 3 right dominant patterns. There was high agreement between classification methods, yet the cluster analysis revealed novel correlations with clinical features. Beyond the established association of left-handedness, early seizure onset, and vascular pathology with atypical language, cluster analysis identified an association of handedness with frontal lateralization, early seizure onset with temporal lateralization, and left hemisphere focus with a unilateral right pattern. Intelligence quotient was not significantly different among patterns.

INTERPRETATION

Language dominance is a continuum; however, our results demonstrate meaningful thresholds in classifying laterality. Atypical language patterns are less frequent but more variable than typical language patterns, posing challenges for accurate presurgical planning. Language dominance should be assessed on a regional rather than hemispheric basis, and clinical characteristics should inform evaluation of atypical language dominance. Reorganization of language is not uniformly detrimental to language functioning.

Brain lateralization and neural plasticity for musical and cognitive abilities in an epileptic musician

The use of intracarotid propofol procedure (IPP) when assessing musical lateralization has not been reported in literature up to now. This procedure (similar to Wada Test) has provided the opportunity to investigate not only lateralization of language and memory functions on epileptic patients but also offers a functional mapping approach with superior spatial and temporal resolution to analyze the lateralization of musical abilities. Findings in literature suggest that musical training modifies functional and structural brain organization. We studied hemispheric lateralization in a professional musician, a 33 years old woman with refractory left medial temporal lobe (MTL) epilepsy (TLE). A longitudinal neuropsychological study was performed over a period of 21 months. Before epilepsy surgery, musical abilities, language and memory were tested during IPP by means of a novel and exhaustive neuropsychological battery focusing on the processing of music. We used a selection of stimuli to analyze listening, score reading, and tempo discrimination. Our results suggested that IPP is an excellent method to determine not only language, semantic, and episodic memory, but also musical dominance in a professional musician who may be candidate for epilepsy surgery. Neuropsychological testing revealed that right hemisphere's patient is involved in semantic and episodic musical memory processes, whereas her score reading and tempo processing require contribution from both hemispheres. At one-year follow-up, outcome was excellent with respect to seizures and professional skills, meanwhile cognitive abilities improved. These findings indicate that IPP helps to predict who might be at risk for postoperative musical, language, and memory deficits after epilepsy surgery. Our research suggests that musical expertise and epilepsy critically modifies long-term memory processes and induces brain structural and functional plasticity.

A surface-based analysis of language lateralization and cortical asymmetry

Among brain functions, language is one of the most lateralized. Cortical language areas are also some of the most asymmetrical in the brain. An open question is whether the asymmetry in function is linked to the asymmetry in anatomy. To address this question, we measured anatomical asymmetry in 34 participants shown with fMRI to have language dominance of the left hemisphere (LLD) and 21 participants shown to have atypical right hemisphere dominance (RLD). All participants were healthy and left-handed, and most (80%) were female. Gray matter (GM) volume asymmetry was measured using an automated surface-based technique in both ROIs and exploratory analyses. In the ROI analysis, a significant difference between LLD and RLD was found in the insula. No differences were found in planum temporale (PT), pars opercularis (POp), pars triangularis (PTr), or Heschl's gyrus (HG). The PT, POp, insula, and HG were all significantly left lateralized in both LLD and RLD participants. Both the positive and negative ROI findings replicate a previous study using manually labeled ROIs in a different cohort [Keller, S. S., Roberts, N., Garcia-Finana, M., Mohammadi, S., Ringelstein, E. B., Knecht, S., et al. Can the language-dominant hemisphere be predicted by brain anatomy? Journal of Cognitive Neuroscience, 23, 2013-2029, 2011]. The exploratory analysis was accomplished using a new surface-based registration that aligns cortical folding patterns across both subject and hemisphere. A small but significant cluster was found in the superior temporal gyrus that overlapped with the PT. A cluster was also found in the ventral occipitotemporal cortex corresponding to the visual word recognition area. The surface-based analysis also makes it possible to disentangle the effects of GM volume, thickness, and surface area while removing the effects of curvature. For both the ROI and exploratory analyses, the difference between LLD and RLD volume laterality was most strongly driven by differences in surface area and not cortical thickness. Overall, there were surprisingly few differences in GM volume asymmetry between LLD and RLD indicating that gross morphometric asymmetry is only subtly related to functional language laterality.

Naming outcome after left or right temporal lobectomy in patients with bilateral language representation by Wada testing

OBJECTIVE

This study aimed to examine language outcome after left or right anterior temporal lobectomy (ATL) in patients with epilepsy with bilateral language representation on intracarotid sodium amobarbital (Wada) testing.

METHODS

Twenty-two patients with epilepsy with bilateral language (Wada laterality index between -50 and 50) underwent right ATL (RATL, n=10) or left ATL (LATL, n=12). All the patients were administered the Boston Naming Test preoperatively and six months postoperatively.

RESULTS

Left anterior temporal lobectomy patients showed greater postoperative naming decline than RATL patients. Group differences were also observed on subtests of the Wada test. Performance on the Wada naming and comprehension subtests was better in the nonsurgical hemisphere than in the surgical hemisphere in the RATL group, but there was no difference between the nonsurgical and the surgical hemisphere naming and comprehension performance in the LATL group.

CONCLUSIONS

Left anterior temporal lobectomy patients with bilateral language are at greater risk for naming decline than RATL patients with bilateral language. This difference may be due to relatively better naming and comprehension abilities in the nonsurgical hemisphere in the RATL group.

Naming outcome prediction in patients with discordant Wada and fMRI language lateralization

OBJECTIVE

Investigations of the validity of fMRI as an alternative to Wada language testing have yielded Wada/fMRI discordance rates of approximately 15%, but almost nothing is known regarding the relative accuracy of Wada and fMRI in discordant cases. The objective of this study was to determine which of the two (the Wada test or the language fMRI) is more predictive of postoperative naming outcome following left anterior temporal lobectomy in discordant cases.

METHODS

Among 229 patients with epilepsy who prospectively underwent Wada and fMRI language testing, ten had discordant language lateralization results, underwent left anterior temporal lobectomy, and returned for postoperative language testing. The relative accuracy of Wada and fMRI for predicting language outcome was examined in these cases.

RESULTS

Functional magnetic resonance imaging provided a more accurate prediction of language outcome in seven patients, Wada was more accurate in two patients, and the two tests were equally accurate in one patient.

CONCLUSIONS

In cases of discordance, fMRI predicted postsurgical naming outcome with relatively better accuracy compared to the Wada test.

Crossed aphasia after right anterior temporal lobectomy. A case report

The occurrence of crossed aphasia as a complication after temporal lobe epilepsy surgery is extremely rare. We report the case of a 47-year-old right-handed patient with drug-resistant mesial temporal lobe epilepsy (MTLE) who developed a transitory aphasic syndrome after a right temporal anterior lobectomy. This syndrome was characterized by anomia, poor verbal fluency, verbal perseveration, and verbal comprehension difficulties. He also showed writing difficulties, reading substitutions, and calculation task errors. The patient was regularly assessed with language tasks, and showed a spontaneous and progressive recovery of his symptoms, with remaining naming difficulties. We discuss the role that epileptogenic zone could play in cortical reorganization of the language systems.

Assessing language dominance with functional MRI: the role of control tasks and statistical analysis

There is a discrepancy between the brain regions revealed by functional neuroimaging techniques and those brain regions where a loss of function, either by lesion or by electrocortical stimulation, induces language disorders. To differentiate between essential and non-essential language-related processes, we investigated the effects of linguistic control tasks and different analysis methods for functional MRI data. Twelve subjects solved two linguistic generation tasks: (1) a verb generation task and (2) an antonym generation task (each with a linguistic control task on the phonological level) as well as two decision tasks of semantic congruency (each with a cognitive high-level control task). Differential contrasts and conjunction analyses were carried out on the single-subject level and an individual lateralization index (LI) was computed. On the group level we determined the percent signal change in the left inferior frontal gyrus (IFG: BA 44 and BA 45). The conjunction analysis of multiple language tasks led to significantly greater absolute LIs than the LIs based on the single task versus fixation contrasts. A further significant increase of the magnitude of the LIs could be achieved by using the phonological control conditions. Although the decision tasks appear to be more robust to changes in the statistical threshold, the combined generation tasks had an advantage over the decision tasks both for assessing language dominance and locating Broca's area. These results underline the need for conjunction analysis based on several language tasks to suppress highly task-specific processes. They also point to the need for high-level cognitive control tasks to partial out general, language supporting but not language critical processes. Higher absolute LIs, which reflect unambiguously hemispheric language dominance, can be thus obtained.

A decisional space for fMRI pattern separation using the principal component analysis--a comparative study of language networks in pediatric epilepsy

Atypical functional magnetic resonance imaging (fMRI) language patterns may be identified by visual inspection or by region of interest (ROI)-based laterality indices (LI) but are constrained by a priori assumptions. We compared a data-driven novel application of principal component analysis (PCA) to conventional methods. We studied 122 fMRI data sets from control and localization-related epilepsy patients provided by five children's hospitals. Each subject performed an auditory description decision task. The data sets, acquired with different scanners but similar acquisition parameters, were processed through fMRIB software library to obtain 3D activation maps in standard space. A PCA analysis was applied to generate the decisional space and the data cluster into three distinct activation patterns. The classified activation maps were interpreted by (1) blinded reader rating based on predefined language patterns and (2) by language area ROI-based LI (i.e., fixed threshold vs. bootstrap approaches). The different classification results were compared through κ inter-rater agreement statistics. The unique decisional space classified activation maps into three clusters (a) lower intensity typical language representation, (b) higher intensity typical, as well as (c) higher intensity atypical representation. Inter-rater agreements among the three raters were excellent (Fleiss κ = 0.85, P = 0.05). There was substantial to excellent agreement between the conventional visual rating and LI methods (κ = 0.69-0.82, P = 0.05). The PCA-based method yielded excellent agreement with conventional methods (κ = 0.82, P = 0.05). The automated and data-driven PCA decisional space segregates language-related activation patterns in excellent agreement with current clinical rating and ROI-based methods.

Language organization and reorganization in epilepsy

The vast majority of healthy individuals are left hemisphere dominant for language; however, individuals with left hemisphere epilepsy have a higher likelihood of atypical language organization. The cerebral organization of language in epilepsy has been studied with invasive procedures such as Wada testing and electrical cortical stimulation mapping (ESM), and more recently, with noninvasive neuroimaging techniques such as functional magnetic resonance imaging (fMRI). Investigators have used these techniques to explore the influence of unique clinical features inherent in epilepsy that might contribute to the reorganization of language, such as location of seizure onset, age of seizure onset, and extent of interictal epileptiform activity. In this paper, we review the contribution of these and other clinical variables to the lateralization and localization of language in epilepsy, and how these patient-related variables affect the results from these three different, yet complementary methodologies. Unlike the abrupt language changes that occur following acute brain injury with disruption of established language circuits, converging evidence suggests that the chronic nature of epileptic activity can result in a developmental shift of language from the left to the right hemisphere or re-routing of language pathways from traditional to non-traditional areas within the dominant left hemisphere. Clinical variables have been shown to contribute to cerebral language reorganization in the setting of chronic seizure disorders, yet such factors have not been reliable predictors of altered language networks in individual patients, underscoring the need for language lateralization and localization procedures when definitive identification of language cortex is necessary for clinical care.

Sub-patterns of language network reorganization in pediatric localization related epilepsy: a multisite study

To study the neural networks reorganization in pediatric epilepsy, a consortium of imaging centers was established to collect functional imaging data. Common paradigms and similar acquisition parameters were used. We studied 122 children (64 control and 58 LRE patients) across five sites using EPI BOLD fMRI and an auditory description decision task. After normalization to the MNI atlas, activation maps generated by FSL were separated into three sub-groups using a distance method in the principal component analysis (PCA)-based decisional space. Three activation patterns were identified: (1) the typical distributed network expected for task in left inferior frontal gyrus (Broca's) and along left superior temporal gyrus (Wernicke's) (60 controls, 35 patients); (2) a variant left dominant pattern with greater activation in IFG, mesial left frontal lobe, and right cerebellum (three controls, 15 patients); and (3) activation in the right counterparts of the first pattern in Broca's area (one control, eight patients). Patients were over represented in Groups 2 and 3 (P < 0.0004). There were no scanner (P = 0.4) or site effects (P = 0.6). Our data-driven method for fMRI activation pattern separation is independent of a priori notions and bias inherent in region of interest and visual analyses. In addition to the anticipated atypical right dominant activation pattern, a sub-pattern was identified that involved intensity and extent differences of activation within the distributed left hemisphere language processing network. These findings suggest a different, perhaps less efficient, cognitive strategy for LRE group to perform the task.

Evidence for the solidarity of the expressive and receptive language systems: a retrospective study

A strong tendency toward left hemisphere (LH) language dominance has been well established, as evidenced by the high prevalence of language impairment following sudden onset lesions in the LH. In the presence of progressive LH pathology, such as epilepsy, substantial deviations in language organization can occur. However, the question regarding whether reorganization involves both expressive and receptive language functions or only the one directly affected by the primary location of pathology has not been settled. Using Wada testing scores from 296 epilepsy patients and estimated rates of typical dominance in the normal population, we assessed the frequency with which left frontal and temporal pathology resulted in reorganization of only the expressive or receptive language function or both. The comparisons revealed: (1) a significantly higher prevalence of atypical organization (i.e., deviations from LH dominance) among the LH patients compared to normal population estimates and right hemisphere patients, and (2) that regardless of pathology location within the LH, the rates of atypical reorganization for both expressive and receptive language were essentially equal. These results constitute evidence that the two language functions are intimately yoked and that when disruption to the system results in reorganization, it usually yields functional changes throughout the system.

Deriving estimates of contralateral footedness from prevalence rates in samples of Brazilian and non-Brazilian right- and left-handers

Although footedness is closely associated with handedness, accurate prevalence rates of contralateral footedness in right- and left-handed populations were previously unavailable to researchers studying the relationship between phenotypic and hemispheric asymmetries. We collected preference data from 2081 Brazilian children and adolescents, and relate the prevalence of crossed hand/foot preferences to values reported elsewhere in the literature. In our samples, about 4% of the dextrals and 33% of the sinistrals exhibited a contralateral kicking preference. This is in close agreement with the weighted means from our analysis of 19 papers in the literature, which yields 4.0% left-footed kicking in dextrals and 33.5% right-footed kicking in sinistrals. These values are in marked contrast to the 50% figure for right-footed kicking in sinistrals as given by MacNeilage and colleagues (1988, 1991). Among Brazilians with mixed handedness, there was a substantial increase in incongruent footedness. Male consistent right- and left-handers showed a higher prevalence of cross-footed preferences in their kicking preference than females. The sex difference in dextrals was attributed to a training effect in soccer-related activities, and to a sampling bias in sinistrals.

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.

The contribution of neuropsychology to diagnostic assessment in epilepsy

Neuropsychology plays a vital role in the treatment of epilepsy, providing information on the effects of seizures on higher cortical functions through the measurement of behavioral abilities and disabilities. This is accomplished through the design, administration and interpretation of neuropsychological tests, including those used in functional neuroimaging or cortical mapping and in intracarotid anesthetic procedures. The objective of this paper is to define and summarize in some detail the role and methods of neuropsychologists in specialized epilepsy centers. Included are information and recommendations regarding basic ingredients of a thorough neuropsychological assessment in the epilepsy setting, as well as suggestions for an abbreviated alternative exam when needed, with emphasis on functions associated with specific brain regions. The paper is intended for novice and experienced neuropsychologists to enable them to develop or evaluate their current practices, and also for other clinicians, who seek a better understanding of the methodology underlying the neuropsychological input to their work.

The role of functional magnetic resonance imaging in brain surgery

New functional neuroimaging techniques are changing our understanding of the human brain, and there is now convincing evidence to move away from the classic and clinical static concepts of functional topography. In a modern neurocognitive view, functions are thought to be represented in dynamic large-scale networks. The authors review the current (limited) role of functional MR imaging in brain surgery and the possibilities of new functional MR imaging techniques for research and neurosurgical practice. A critique of current clinical gold standard techniques (electrocortical stimulation and the Wada test) is given.

Sensitivity and reliability of language laterality assessment with a free reversed association task--a fMRI study

OBJECTIVE

The aim of the study was to evaluate the sensitivity and reliability of assessing hemispheric language dominance with functional magnetic resonance imaging (fMRI) using a 'free reversed association task.'

METHODS

Thirty-nine healthy subjects (13 dextrals, 13 sinistrals and 13 bimanuals) underwent two repeated fMRI sessions. In the active phases sets of words were presented via headphones, and an associated target item was named. During the baseline phases a standard answer was given after listening to unintelligible stimuli. Data were preprocessed with SPM, and then laterality indices (LI) and reliability coefficients (RC) were calculated.

RESULTS

Extensive frontal, temporal and parietal activations were found. Seventy-eight percent of the subjects showed left-hemispheric dominance, 5% showed right-hemispheric dominance, and 17% had bilateral language representations. The incidence of right-hemispheric language dominance was 4.3 times higher in a left-hander with a handedness quotient (HQ) of -90 than in a right-hander with a HQ of +90. The RC was 0.61 for combined ROIs (global network). Strong correlations were found between the two session LIs (r = 0.95 for the global network).

CONCLUSION

'Free reversed association' is a sensitive and reliable task for the determination of individual language lateralization. This suggests that the task may be used in a clinical setting.

Bilateral and independent Broca areas confirmed by Wada test and functional magnetic resonance imaging

Accurate preoperative evaluation of language dominance is critical when evaluating potential patients for temporal lobe epilepsy surgery. Although most people have left-sided language dominance, a minority of patients have been described with either bilateral or right hemispheric dominance. We present a patient with right temporal lobe epilepsy who presented with bilateral and functionally independent Broca areas, as confirmed by Wada testing and functional magnetic resonance imaging.

The connectivity of the superior longitudinal fasciculus: a tractography DTI study

PURPOSE

The left superior longitudinal fasciculus (SLF) has been felt to link receptive with expressive language areas. The latter is located in the pars opercularis (Broca's area) of the left inferior frontal gyrus. We report the findings with tractography of the SLF in a group of normal volunteers.

METHODS AND MATERIALS

The data and subsidiary results of 12 normal right-handed volunteers who participated in an institutional review board-approved diffusion tensor imaging study were evaluated. The SLF fibers were obtained bilaterally placing a region of interest at the triangular-shaped region lateral to each of the corticospinal tracts, in a coronal plane along the rostral aspect of the corpus callosum. A sagittal fractional anisotropy image was used to determine the rostral endpoint of the SLF fibers in the white matter pertaining to specific gyri or pars of the frontal lobe. The SLF projection to Broca's area was ranked qualitatively as none, minimal, most or all. Findings are presented in descriptive statistics.

RESULTS

The SLF projection to Broca's areas was absent in seven subjects (58.3%) and minimal in five (41.6%). SLF's rostral end points were found uniquely or mainly in the precentral gyrus in 100% of cases.

CONCLUSION

The SLF was found connecting the posterior language areas to the precentral gyrus and only marginally in some cases to the canonical Broca's area. This finding is consistent with reports describing lack of correlation between lateralization of the SLF and language areas. The understanding of language circuitry is beginning to emerge with the use of tractography.

The role of the arcuate fasciculus in conduction aphasia

In aphasia literature, it has been considered that a speech repetition defect represents the main constituent of conduction aphasia. Conduction aphasia has frequently been interpreted as a language impairment due to lesions of the arcuate fasciculus (AF) that disconnect receptive language areas from expressive ones. Modern neuroradiological studies suggest that the AF connects posterior receptive areas with premotor/motor areas, and not with Broca's area. Some clinical and neurophysiological findings challenge the role of the AF in language transferring. Unusual cases of inter-hemispheric dissociation of language lateralization (e.g. Broca's area in the left, and Wernicke's area in the right hemisphere) have been reported without evident repetition defects; electrocortical studies have found that the AF not only transmits information from temporal to frontal areas, but also in the opposite direction; transferring of speech information from the temporal to the frontal lobe utilizes two different streams and conduction aphasia can be found in cases of cortical damage without subcortical extension. Taken altogether, these findings may suggest that the AF is not required for repetition although could have a subsidiary role in it. A new language network model is proposed, emphasizing that the AF connects posterior brain areas with Broca's area via a relay station in the premotor/motor areas.

Language lateralization in epilepsy patients: fMRI validated with the Wada procedure

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 (LIs) 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.

Functional MRI and Wada studies in patients with interhemispheric dissociation of language functions

Rare patients with chronic epilepsy show interhemispheric dissociation of language functions on intracarotid amobarbital (Wada) testing. We encountered four patients with interhemispheric dissociation in 490 consecutive Wada language tests. In all cases, performance on overt speech production tasks was supported by the hemisphere contralateral to the seizure focus, whereas performance on comprehension tasks was served by the hemisphere with the seizure focus. These data suggest that speech production capacity is more likely to shift hemispheres than is language comprehension. Wada and fMRI language lateralization scores were discordant in three of the four patients. However, the two methods aligned more closely when Wada measures loading on comprehension were used to calculate lateralization scores. Thus, interhemispheric dissociation of language functions could explain some cases of discordance on Wada/fMRI language comparisons, particularly when the fMRI measure used is not sensitive to speech production processes.

Unexpected right hemisphere language representation identified by the intracarotid amobarbital procedure in right-handed epilepsy surgery candidates

The intracarotid amobarbital procedure (IAP) is used for language lateralization in the presurgical evaluation for intractable epilepsy. Some epilepsy surgical centers forgo IAP for right temporal lobectomies in right-handed patients with no personal/family history of left-handedness, implying that right hemisphere language representation does not occur in these patients. To test this hypothesis, a retrospective analysis was performed on 156 consecutive epilepsy surgery candidates who underwent IAP. Of the 156 candidates, 122 were right-handed, and 55 of the 122 demonstrated right hemisphere seizure focus. Right hemisphere language representation was found in 22 of 55 patients, with two demonstrating significant right hemisphere language despite a right hemisphere seizure focus and no family history of left-handedness. Only 1 of 156 patients undergoing IAP experienced permanent neurological complications. Although relatively uncommon, right hemisphere language representation may occur more frequently than complications from cerebral angiography and, therefore, presurgical IAP is recommended for all epilepsy surgery candidates regardless of handedness to minimize the risk of severe language decline.

Priming vs. rhyming: orthographic and phonological representations in the left and right hemispheres

The right cerebral hemisphere has long been argued to lack phonological processing capacity. Recently, however, a sex difference in the cortical representation of phonology has been proposed, suggesting discrete left hemisphere lateralization in males and more distributed, bilateral representation of function in females. To evaluate this hypothesis and shed light on sex differences in the phonological processing capabilities of the left and right hemispheres, we conducted two experiments. Experiment 1 assessed phonological activation implicitly (masked homophone priming), testing 52 (M=25, F=27; mean age 19.23years, SD 1.64years) strongly right-handed participants. Experiment 2 subsequently assessed the explicit recruitment of phonology (rhyme judgement), testing 50 (M=25, F=25; mean age 19.67years, SD 2.05years) strongly right-handed participants. In both experiments the orthographic overlap between stimulus pairs was strictly controlled using DICE [Brew, C., & McKelvie, D. (1996). Word-pair extraction for lexicography. In K. Oflazer & H. Somers (Eds.), Proceedings of the second international conference on new methods in language processing (pp. 45-55). Ankara: VCH], such that pairs shared (a) high orthographic and phonological similarity (e.g., not-KNOT); (b) high orthographic and low phonological similarity (e.g., pint-HINT); (c) low orthographic and high phonological similarity (e.g., use-EWES); or (d) low orthographic and low phonological similarity (e.g., kind-DONE). As anticipated, high orthographic similarity facilitated both left and right hemisphere performance, whereas the left hemisphere showed greater facility when phonological similarity was high. This difference in hemispheric processing of phonological representations was especially pronounced in males, whereas female performance was far less sensitive to visual field of presentation across both implicit and explicit phonological tasks. As such, the findings offer behavioural evidence indicating that though both hemispheres are capable of orthographic analysis, phonological processing is discretely lateralised to the left hemisphere in males, but available in both the left and right hemisphere in females.

Language brain dominance in patients with refractory temporal lobe epilepsy: a comparative study between functional magnetic resonance imaging and dichotic listening test

PURPOSE: To identify brain dominance for language functions with DLT and correlate these results with those obtained from fMRI in patients suffering from intractable temporal lobe epilepsy. METHOD: This study reports on 13 patients who underwent pre-surgical epileptic evaluation between April and October 2004 at the Epilepsy Surgery Program, Hospital Sao Lucas, PUCRS. In DLT, dominance was assessed through a consonant-vowel task, whereas in fMRI patients performed a verb generation task. RESULTS: Our results identified a correlation between the fMRI lateralization index and the DLT ear predominance index and reply difference index (r=0.6, p=0.02; Pearson Correlation Coefficient), showing positive correlation between results obtained from fMRI and DLT. CONCLUSION: DLT was found to significantly correlate with fMRI. These findings indicate that DLT (a non-invasive procedure) could be a useful tool to evaluate language brain dominance in pre-surgical epileptic patients as it is cheaper to perform than fMRI.

What's "right" in language comprehension: ERPs reveal right hemisphere language capabilities

Although the term "nonverbal" is often applied to the right cerebral hemisphere (RH), a growing body of work indicates that the RH can comprehend language and, indeed, that it makes critical contributions to normal language functions. Reviewed here are studies that have examined RH language capabilities by combining visual half-field presentation methods with event-related potential (ERP) measures. Because they afford temporal and functional specificity and can be obtained as participants simply process language for meaning, ERPs provide especially valuable insights into RH language functions. Such studies suggest that the RH appreciates word and message-level meaning information, and that it may play a particularly important role in the processing of relatively unpredictable semantic relationships. In addition, this work suggests that patterns observed for everyday language processing may often be an emergent property of multiple, distinct mechanisms operating in parallel as the left and right hemispheres jointly comprehend language.

Functional magnetic resonance imaging of language in epilepsy

Functional magnetic resonance imaging (fMRI) has revolutionized our understanding of functional networks and cerebral organization in both normal and pathological brains. In the present review, we describe the use of fMRI for mapping language in epilepsy patients prior to surgical intervention including a discussion of methodological issues and task design, comparisons between fMRI and the intracarotid sodium amobarbital test, fMRI studies of language reorganization, and the use of fMRI laterality indexes to predict outcome after anterior temporal lobectomy.

An update on determination of language dominance in screening for epilepsy surgery: the Wada test and newer noninvasive alternatives

The intracarotid amobarbital procedure or Wada test has been the gold standard for lateralization of language dominance before epilepsy surgery. It is based on deactivation of language cortex with intracarotid anesthesia. However, it is an invasive test with risks and discomforts, and it also has limitations. There has been great interest in replacing the Wada test with a noninvasive procedure. One alternative, repetitive magnetic stimulation works by deactivating language cortex, but most other promising alternatives are based on brain activation. Functional magnetic resonance imaging (fMRI), 15O-water positron emission tomography, single photon emission computerized tomography, transcranial Doppler, and near infrared spectroscopy detect hemodynamic responses to language cortex activation, while magnetoencephalography more directly measures event-related physiological activation. Some of the techniques also provide localization of language functions, whereas the Wada test is strictly a lateralization method. Based on widespread availability, fMRI will likely be the most widely used alternative.

Role of Functional MR in Determining Language Dominance in Epilepsy and Nonepilepsy Populations: A Bayesian Analysis

PURPOSE

To determine the role of functional magnetic resonance (MR) imaging in assessing hemispheric language dominance in epilepsy and nonepilepsy populations.

MATERIALS AND METHODS

A Bayesian analysis study was performed. The study was based on data from the published literature; thus, institutional review board approval was not required. The literature was reviewed to obtain pretest probabilities and likelihood ratios, which were analyzed to determine the posttest probability of language dominance by using functional MR imaging. Pretest probabilities of different hand dominances in epilepsy and nonepilepsy populations were obtained from the largest studies available in the literature. Likelihood ratios were derived from the sensitivity and specificity of functional MR imaging by using electrocortical stimulation (ECS) and the Wada test as reference standards.

RESULTS

Likelihood ratios for functional MR in determining language dominance were 9.3 and 12.3 with ECS and the Wada test as reference standards, respectively. Use of functional MR increased the final posttest probabilities of hemispheric language dominance in epilepsy and nonepilepsy populations. In the nonepilepsy population, regardless of hand dominance, there was very high posttest probability (>or=96%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the epilepsy population with right-hand dominance or ambidexterity, there was very high posttest probability (>or=95%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the left-handed nonepileptic subjects, there was high posttest probability (81%-83%) of a correlation between functional MR hemisphere activation and definite right-hemisphere language dominance. In the left-handed epilepsy population, there was high posttest probability (80%-97%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the epilepsy population with ambidexterity, there was high posttest probability (80%-87%) of correlations between functional MR hemisphere activation and both definite right-hemisphere and bilateral language dominance.

CONCLUSION

Use of functional MR increases importantly the posttest probabilities of hemispheric language dominance in multiple subgroups of individuals with and without epilepsy.

Determining language laterality by fMRI and dichotic listening

For imaging studies on hemispheric specialization of the human brain, data about known functional asymmetries other than handedness would be valuable for a reliable interpretation of lateralized activation in individuals or groups of subjects. As certain aspects of language processing are observed to be a function of primarily the left, it can be used as a reference for other asymmetric processes such as sensory or cognitive skills. For analyzing language laterality, there are a variety of methods, but these differ in application or accuracy. In this study, we tested the reliability of two widely used methods - dichotic listening and fMRI - to determine language dominance in 30 individual subjects. The German adaptation of a dichotic listening test (Hättig, H., Beier, M., 2000. FRWT: a dichotic listening test for clinical and scientific contexts, Zeitschr f Neuropsychologie 11. 233-245.) classified 54% of the 26 right-handed subjects as left hemispheric dominant. The results of the fMRI paradigm (Fernández, G., de Greiff, A., von Oertzen, J., et al., 2001. Language mapping in less than 15 min: real-time functional MRI during routine clinical investigation. Neuroimage 14, 585-594.) tested on the same subjects, however, classified 92% of the right-handed subjects as left dominant. The main reason for this discrepancy was that the ear dominance score of many subjects in the dichotic listening test was too low to determine a reliable ear advantage. As a consequence, this specific dichotic listening test cannot be used to determine language laterality in individual subjects. On the other hand, the fMRI results are consistent with numerous studies showing left dominant language processing in more than 90% of right-handers. In some subjects, however, language laterality critically depends on the areas used to determine the laterality index.

fMRI evaluation of hemispheric language dominance using various methods of laterality index calculation

Several functional MR imaging studies evaluating the lateralisation of linguistic functions in patients who underwent Wada testing have been reported. There is extensive variance in the Laterality index (LI) calculation across the studies, and the optimal calculation method remains unclear. We attempted to calculate the LI in different ways in the same subjects, in order to find the LI calculation method with the highest correlation to the Wada test. Fifteen patients (10 females, 5 males) suffering from medically intractable temporal lobe epilepsy (TLE) (12 left, 3 right) were admitted for the study. The patients underwent a standardized bilateral intracarotid short-acting barbiturate test. Language testing included spontaneous speech, oral comprehension, reading, object and picture naming, and repetition. All the tasks were scored separately in order to increase the possibility of correlation between Wada and LI. A silent phonemic verbal fluency task (VFT) was used as a language paradigm for functional measurement. Regions of interest (ROIs), with a known association with language function (Broca's area, the lateral prefrontal cortex, etc.), were defined. First, the LIs were calculated from the ROIs using a previously reported method (simple suprathreshold count). Next, we used several new methods of LI calculation (t-weighting of voxels, methods independent of the choice of the statistical threshold, etc.) The most significant correlation with Wada was proven in the LIs that were evaluated from Broca's area (up to R = 0.94, P = 1 x 10(-7)). However, the new LI calculation methods used in the present study did not produce a statistically significant benefit in comparison to previously reported methods.

Language lateralization of Chinese-English bilingual patients with temporal lobe epilepsy: a functional MRI study

Functional MRI was used to examine language lateralization of Chinese characters and English words associated with temporal lobe epilepsy (TLE) in Chinese-English bilinguals with left or right TLE. The results suggest that the neural basis of processing Chinese and English seems to be different, as normal controls demonstrated left hemispheric lateralization in reading English words but bi-hemispheric lateralization in reading Chinese characters. This difference in the neural bases of Chinese and English processing was found to affect the patterns in change-of-language processing associated with TLE. That is, whereas left-TLE patients were more likely than right-TLE patients to demonstrate a bi-hemispheric language involvement in reading English, both left- and right-TLE patients demonstrated primarily bilateral hemispheric involvement for reading Chinese characters.