Language Lateralization in Patients with Temporal Lobe Epilepsy : A Comparison between Volumetric Analysis and the Wada Test

Objective

Determining language lateralization is important for the presurgical evaluation of patients with medically intractable epilepsy. The Wada test has been the gold standard for lateralization of language dominance before epilepsy surgery. However, it is an invasive test with risk, and have some limitations.

Methods

We compared the volumetric analysis with Wada test, and studied the clinical potential of volumetric analysis to assess language laterality in large surgical candidates with temporal lobe epilepsy (TLE). To examine the efficacy of volumetric analysis to determine language lateralization during presurgical evaluation, we compared the volumetric analysis of the bilateral planum temporale with the results of Wada test in 59 patients with chronic intractable TLE (rTLE, n=32; lTLE, n=27) who underwent epilepsy surgery. We measured the gray matter volumes of planum temporale (PT) of each patients using the VoxelPlus2 program (Mevisys, Daejeon, Korea).

Results

Overall congruence of the volumetric analysis with the Wada test was 97.75% in rTLE patients and 81.5% in lTLE patients. There were more significant leftward asymmetry of the PT in rTLE patients than lTLE patients. In lTLE patients, relatively high proportion (37%) of the patients showed bilateral or right hemispheric language dominance.

Conclusion

These results provide evidence that the volumetric analysis of the PT could be used as an alternatives in language lateralization. Also, the results of the Wada test suggested that there was considerable plasticity of language representation in the brains of patients with intractable TLE and it was associated with an earlier age of brain injury.     

Lesion side matters — An fMRI study on the association between neural correlates of watching dynamic fearful faces and their evaluation in patients with temporal lobe epilepsy

Most studies assessing facial affect recognition in patients with TLE reported emotional disturbances in patients with TLE. Results from the few fMRI studies assessing neural correlates of affective face processing in patients with TLE are divergent. Some, but not all, found asymmetrical mesiotemporal activations, i.e., stronger activations within the hemisphere contralateral to seizure onset. Little is known about the association between neural correlates of affect processing and subjective evaluation of the stimuli presented. Therefore, we investigated the neural correlates of processing dynamic fearful faces in 37 patients with mesial temporal lobe epilepsy (TLE; 18 with left-sided TLE (lTLE), 19 with right-sided TLE (rTLE)) and 20 healthy subjects. We additionally assessed individual ratings of the fear intensity and arousal perception of the fMRI stimuli and correlated these data with the activations induced by the fearful face paradigm and activation lateralization within the mesiotemporal structures (in terms of individual lateralization indices, LIs). In healthy subjects, whole-brain analysis showed bilateral activations within a widespread network of mesial and lateral temporal, occipital, and frontal areas. The patient groups activated different parts of this network. In patients with lTLE, we found predominantly right-sided activations within the mesial and lateral temporal cortices and the superior frontal gyrus. In patients with rTLE, we observed bilateral activations in the posterior regions of the lateral temporal lobe and within the occipital cortex. Mesiotemporal region-of-interest analysis showed bilateral symmetric activations associated with watching fearful faces in healthy subjects. According to the region of interest and LI analyses, in the patients with lTLE, mesiotemporal activations were lateralized to the right hemisphere. In the patients with rTLE, we found left-sided mesiotemporal activations. In patients with lTLE, fear ratings were comparable to those of healthy subjects and were correlated with relatively stronger activations in the right compared to the left amygdala. Patients with rTLE showed significantly reduced fear ratings compared to healthy subjects, and we did not find associations with amygdala lateralization. Although we found stronger activations within the contralateral mesial temporal lobe in the majority of all patients, our results suggest that only in the event of left-sided mesiotemporal damage is the right mesial temporal lobe able to preserve intact facial fear recognition. In the event of right-sided mesiotemporal damage, fear recognition is disturbed. This underlines the hypothesis that the right amygdala is biologically predisposed to processing fear, and its function cannot be fully compensated in the event of right-sided mesiotemporal damage.     

Language dominance determined by whole brain functional MRI in patients with brain lesions

BACKGROUND: Functional MRI (fMRI) is of potential value in determining hemisphere dominance for language in epileptic patients. OBJECTIVE: To develop and validate an fMRI-based method of determining language dominance for patients with a wide range of potentially operable brain lesions in addition to epilepsy. METHODS: Initially, a within-subjects design was used with 19 healthy volunteers (11 strongly right-handed, 8 left-handed) to determine the relative lateralizing usefulness of three different language tasks in fMRI. An automated, hemispheric analysis of laterality was used to analyze whole brain fMRI data sets. To evaluate the clinical usefulness of this method, we compared fMRI-determined laterality with laterality determined by Wada testing or electrocortical stimulation mapping, or both, in 23 consecutive patients undergoing presurgical evaluation of language dominance. RESULTS: Only the verb generation task was reliably lateralizing. fMRI, using the verb generation task and an automated hemispheric analysis method, was concordant with invasive measures in 22 of 23 patients (12 Wada, 11 cortical stimulation). For the single patient who was discordant, in whom a tumor involved one-third of the left hemisphere, fMRI became concordant when the tumor and its reflection in the right hemisphere were excluded from laterality analysis. No significant negative correlation was obtained between lesion size and strength of laterality for the patients with lesions involving the dominant hemisphere. CONCLUSION: This fMRI method shows potential for evaluating language dominance in patients with a variety of brain lesions.     

Language lateralization in temporal lobe epilepsy using functional MRI and probabilistic tractography

Purpose: Language functional magnetic resonance imaging (fMRI) is used to noninvasively assess hemispheric language specialization as part of the presurgical work-up in temporal lobe epilepsy (TLE). White matter asymmetries on diffusion tensor imaging (DTI) may be related to language specialization as shown in controls and TLE. To refine our understanding of the effect of epilepsy on the structure–function relationships, we focused on the arcuate fasciculus (ArcF) and the inferior occipitofrontal fasciculus (IOF) and tested the relationship between DTI- and fMRI-based lateralization indices in TLE.
Methods: fMRI with three language tasks and DTI were obtained in 20 patients (12 right and 8 left TLE). The ArcF, a major language-related tract, and the IOF were segmented bilaterally using probabilistic tractography to obtain fractional anisotropy (FA) lateralization indices. These were correlated with fMRI-based lateralization indices computed in the inferior frontal gyrus (Pearson's correlation coefficient).
Results: fMRI indices were left-lateralized in 16 patients and bilateral or right-lateralized in four. In the ArcF, FA was higher on the left than on the right side, reaching significance in right but not in left TLE. We found a positive correlation between ArcF anisotropy and fMRI-based lateralization indices in right TLE (p < 0.009), but not in left TLE patients. No correlation was observed for the IOF.
Conclusions: Right TLE patients with more left-lateralized functional activations also showed a leftward-lateralized arcuate fasciculus. The decoupling between the functional and structural indices of the ArcF underlines the complexity of the language network in left TLE patients.     

Language lateralization correlates with verbal memory performance in children with focal epilepsy

Purpose: Assessment of language dominance with functional magnetic resonance imaging (fMRI) and neuropsychological evaluation is often used prior to epilepsy surgery. This study explores whether language lateralization and cognitive performance are systematically related in young patients with focal epilepsy. Methods: Language fMRI and neuropsychological data (language, visuospatial functions, and memory) of 40 patients (7–18 years of age) with unilateral, refractory focal epilepsy in temporal and/or frontal areas of the left (n = 23) or right hemisphere (n = 17) were analyzed. fMRI data of 18 healthy controls (7–18 years) served as a normative sample. A laterality index was computed to determine the lateralization of activation in three regions of interest (frontal, parietal, and temporal). Results: Atypical language lateralization was demonstrated in 12 (30%) of 40 patients. A correlation between language lateralization and verbal memory performance occurred in patients with left‐sided epilepsy over all three regions of interest, with bilateral or right‐sided language lateralization being correlated with better verbal memory performance (Word Pairs Recall: frontal r = ?0.4, p = 0.016; parietal r = ?0.4, p = 0.043; temporal r = ?0.4, p = 0.041). Verbal memory performance made the largest contribution to language lateralization, whereas handedness and side of seizures did not contribute to the variance in language lateralization. Discussion: This finding reflects the association between neocortical language and hippocampal memory regions in patients with left‐sided epilepsy. Atypical language lateralization is advantageous for verbal memory performance, presumably a result of transfer of verbal memory function. In children with focal epilepsy, verbal memory performance provides a better idea of language lateralization than handedness and side of epilepsy and lesion.     

Unsuspected atypical hemispheric dominance for language as determined by fMRI

PURPOSE: We sought to illustrate the value of functional magnetic resonance imaging (fMRI) in the presurgical assessment of hemispheric dominance for language by means of an illustrative case report. METHODS: fMRI with two language paradigms was performed in a right-handed patient without familial sinistrality suffering from a left frontal focal epilepsy. RESULTS: Both fMRI paradigms revealed unequivocally lateralized right hemispheric activation. Atypical language representation was confirmed by Wada test. The further presurgical workup could be restricted to subdural strip recordings instead of the initially intended grid implantation. After resective surgery, no language deficits were apparent. CONCLUSIONS: Hemispheric dominance for language should be assessed by fMRI in all patients before surgery in areas potentially relevant for language in either cerebral hemisphere. fMRI may influence the further diagnostic workup and should be performed before other invasive diagnostic procedures.     

Unilateral intracarotid amobarbital procedure for language lateralization

PURPOSE: The determination of language dominance as part of the presurgical workup of patients with pharmacoresistant epilepsies has experienced fundamental changes. With the introduction of noninvasive functional magnetic resonance imaging (fMRI), the number of patients receiving intracarotid amobarbital procedures (IAPs) for assessment of language dominance has decreased considerably. However, recent studies show that because of methodologic limitations of fMRI, IAP remains an important tool for language lateralization. The current study examines whether unilateral instead of bilateral IAP is an adequate way to apply IAP with reduced invasiveness. METHODS: We retrospectively examine the predictive value of unilateral IAP for the results of bilateral IAP based on a sample of 75 patients with various types of language dominance. Target parameters are the prediction of the language-dominant hemisphere and the identification of patients with atypical language dominance. For language assessment based on unilateral IAP, we introduce the measure hemispheric language capacity (HLC). RESULTS: Unilateral IAP performed on the side of intended surgery quantifies language capacity contralateral to the intended surgery. It detects atypical (bilateral or right) language dominance in the majority of patients. Experience with a separate series of 107 patients requiring presurgical language lateralization shows that in >80%, bilateral IAPs are redundant. CONCLUSIONS: Unilateral IAP is principally sufficient for language lateralization in the presurgical evaluation of patients with pharmacoresistant epilepsies. Necessity of bilateral IAP is restricted to few indications (e.g., callosotomy). In times of noninvasive language lateralization, we propose unilateral IAP as the method of choice for the verification of doubtful (bilateral) fMRI activation patterns.     

丙泊酚wada试验与功能磁共振在癫痫语言优势侧评估中的应用

目的探讨丙泊酚wada试验与fMRI在术前语言优势侧评估中的一致性与预测术后言语及整体智力变化的敏感性。方法对8名左颞叶癫痫患者术前丙泊酚Wada试验和fMRI语言优势侧结果进行比较,独立样本t检验比较两种方法判定的左侧优势组与非左侧优势组手术前后平均VIQ、FIQ变化的差异。结果两者语言优势侧判定一致率为71%,fMRI语言优势为左侧的患者术后平均FIQ、VIQ下降较非左侧组患者显著(P≤0.05),丙泊酚wada试验分组则无显著差异(P>0.05)。结论丙泊酚wada试验与fMRI在癫痫术前语言功能评估中有较高的一致性,从微创、经济和偏侧化预测的一致性及敏感性角度综合考虑,fMRI比Wada试验的优势更明显。     

Lateralization of language function in epilepsy patients: A high-density scalp-derived event-related potentials (ERP) study

Objectives

Language functional magnetic resonance imaging (fMRI) represents the clinical standard for language lateralization assessment in presurgical epilepsy evaluation, but still many patients experience postoperative language deficits. Event-related potentials (ERPs), especially the negative component around and after 400 ms, are related to language processing and could therefore represent a complementary method of language lateralization assessment.

Strongly lateralized activation in language fMRI of atypical dominant patients-implications for presurgical work-up

PURPOSE: Functional magnetic resonance imaging (fMRI) is being used increasingly for language dominance assessment in the presurgical work-up of patients with pharmacoresistant epilepsy. However, the interpretation of bilateral fMRI-activation patterns is difficult. Various studies propose fMRI-lateralization index (LI) thresholds between +/-0.1 and +/-0.5 for discrimination of atypical from typical dominant patients. This study examines if these thresholds allow identifying atypical dominant patients with sufficient safety for presurgical settings. METHODS: 65 patients had a tight comparison, fully controlled semantic decision fMRI-task and a Wada-test for language lateralization. According to Wada-test, 22 were atypical language dominant. In the remaining, Wada-test results were compatible with unilateral left dominance. We determined fMRI-LI for two frontal and one temporo-parietal functionally defined, protocol-specific volume of interest (VOI), and for the least lateralized of these VOIs ("low-VOI") in each patient. RESULTS: We find large intra-individual LI differences between functionally defined VOIs irrespective of underlying type of language dominance (mean LI difference 0.33+/-0.35, range 0-1.6; 15% of patients have inter-VOI-LI differences >1.0). Across atypical dominant patients fMRI-LI in the Broca's and temporo-parietal VOI range from -1 to +1, in the "remaining frontal" VOI from -0.93 to 1. The highest low-VOI-LI detected in atypical dominant patients is 0.84. CONCLUSIONS: Large intra-individual inter-VOI-LI differences and strongly lateralized fMRI-activation in patients with Wada-test proven atypical dominance question the value of the proposed fMRI-thresholds for presurgical language lateralization. Future studies have to develop strategies allowing the reliable identification of atypical dominance with fMRI. The low-VOI approach may be useful.     

Stimulus type affects Wada memory performance

The effects of amytal injection side, seizure focus laterality, and stimulus type (real and line-drawn objects, printed words, and faces) on recognition memory were studied during the Wada procedure. To-be-remembered stimuli were presented during cerebral anesthesia to 35 patients with left temporal lobe epilepsy (LTLE) and 28 patients with right temporal lobe epilepsy (RTLE), all with left hemisphere language dominance. In both groups, recognition of real and line-drawn objects was best after anesthetization of the lesional hemisphere. Recognition of faces was poor after either injection in patients with RTLE, but only after right injection in patients with LTLE. Conversely, recognition of words by patients with LTLE was impaired equally after either injection, but more so after left than right injection in patients with RTLE. The findings suggest that (1) real and line-drawn objects are "dually encoded" and memory accuracy depends on seizure focus laterality, and (2) accuracy in recognition of words and faces is related to seizure focus laterality, but may also depend on the language dominance of the hemisphere being assessed.     

Use of functional MRI in epilepsy]

For the purpose of examining pathophysiological mechanisms of a memory function in epileptic patients or an utility of fMRI for a presurgical assessment in neurosurgical treatment of epilepsy, activated areas in fMRI during verbal or visual memory task were investigated in patient group of temporal lobe epilepsy and normal subject group. Patient group of temporal lobe epilepsy consisted of 7 cases, of which 3 and 3 cases had left and right temporal foci, respectively, except 1 case having undetermined laterality of temporal foci. Normal subjects were 16 cases. All the epileptic and normal subjects were right-handed except for 1 lefty normal subject. Verbal memory tasks were composed of covert and overt recall tasks of 10 words given auditorily, while visual ones were recall tasks of 6 figures given visually. Eventually, in normal subjects, the left side-dominant medial frontal lobes including the superior frontal and anterior cingulate gyri were mainly activated in fMRI during the covert recall tasks of verbal memory, while the left side-dominant inferior frontal and precentral gyri as the motor language areas were chiefly activated in addition to the medial frontal lobe during the overt recall tasks. Further, the bilateral occipital lobes were activated in fMRI during the recall tasks of visual memory. Also in patient groups of temporal lobe epilepsy, the activated areas in fMRI during these tasks were the same as in normal subject group, regardless of the laterality of epileptic temporal foci. These results suggest that fMRI is useful for the determination of the lateralization of the cerebral hemisphere contributing to verbal memory function and therefore for the presurgical assessment of memory function in neurosurgical treatment of epilepsy.     

The utility of functional magnetic resonance imaging in epilepsy and language

Functional magnetic resonance imaging (fMRI) is a viable presurgical tool for use with the pediatric epilepsy population as replacement for the intra-carotid sodium amobarbital test (IAT) used to identify hemispheric language dominance. This paper reviews the current imaging research on the identification of language cortex in pediatric epilepsy patients and in normal children. A review of the literature comparing fMRI to the IAT and electrocortical stimulation suggests that fMRI reliably identifies the dominant hemisphere, with pediatric and adult studies producing comparable results. Within-hemisphere localization of eloquent cortex with fMRI is more problematic. Paradigm selection, data analysis techniques, and considerations specific to imaging children are discussed. Utility of fMRI for studying neural plasticity as a result of brain insult (eg, epilepsy) is also considered.     

Shift-back of right into left hemisphere language dominance after control of epileptic seizures: evidence for epilepsy driven functional cerebral organization

Atypical, i.e. right hemisphere language dominance is frequently observed in early onset left hemisphere epilepsies. In left mesial temporal lobe epilepsy, where eloquent cortex is not directly involved, it is a matter of debate, to which degree atypical language dominance is driven not only by morphological lesions but also by epileptic dysfunction, and whether atypical dominance is hardwired or not. Taking this as the background this study evaluated the hypothesis that epilepsy driven atypical dominancy might be reversible when seizures are successfully controlled. This was evaluated in patients with left mesial temporal lobe epilepsy, who were atypically language dominant by means of language fMRI before surgery, and became seizure free after left selective amygdalo-hippocampectomy. Three out of 53 consecutive atypically dominant patients with chronic epilepsy fulfilled these criteria. Postoperative follow-up language fMRI indicated reversal of right into left dominance in one patient going along with unexpected losses in verbal memory performance. The two other patients experienced unchanged or even enhancement of the pre-existing dominance pattern, going along with consistent postoperative performance changes in cognition. The data thus provide supporting evidence that atypical language dominance can indeed be functionally driven and moreover that in at least some patients, right hemispheric language can shift-back to the left hemisphere when the driving factor, i.e. seizures, becomes successfully controlled. The results have clinical implications for outcome prediction after brain surgery in atypically dominant patients with epilepsy. However, further research in larger groups of atypically dominant patients is required to identify the conditions under which atypical dominance becomes hardwired and when not.     

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.     

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

Memory difficulties are a frequent cognitive complaint of patients with chronic epilepsy. Previous studies have suggested that the presence of a seizure focus causes reorganization of brain mechanisms underlying memory function. Here we examine whether seizure onset in the left hemisphere and onset in the right hemisphere have different effects on memory lateralization and whether longer duration of epilepsy is associated with increased lateralization of memory functions to the unaffected hemisphere. We hypothesized that hemisphere of onset and duration of epilepsy would influence plasticity of memory mechanisms, similar to the plasticity observed for language mechanisms. Healthy controls (HC, N = 10) and patients with epilepsy (N = 23, 11 with a left- and 12 with a right-hemisphere focus) performed a scene-encoding fMRI task at 4 T. Active voxels (relative to scrambled image viewing) were identified for each participant. Memory laterality indices (LIs) were calculated in three regions of interest (ROIs) designed on the basis of HC group data: a functional ROI, an anatomical-hippocampal ROI, and an anatomical-medial temporal ROI encompassing hippocampus and parahippocampal gyrus. In healthy controls, LIs were suggestive of slight left lateralization of encoding memory for pictures. Patients with right hemisphere epilepsy showed a nonsignificant increase in degree of left lateralization. In contrast, patients with left hemispheric epilepsy showed right-lateralized activation, differing significantly from controls and from patients with right hemispheric epilepsy. Neuropsychological measures of memory (WMS-III Story Recall) across epilepsy patients predicted LIs in the anatomical ROIs: higher scores were associated with more left-lateralized medial temporal fMRI activation. Neither age of onset nor duration of epilepsy was significantly related to LI. These results indicate that focal epilepsy may influence the functional neuroanatomy of memory function.     

The effect of seizure focus on regional language processing areas

Purpose: To determine the effect of seizure focus location within the left hemisphere on the expression of regional language dominance. Methods: In this cross‐sectional study we investigated 90 patients (mean age 23.3 ± 12.9 years) with left hemisphere focal epilepsy (mean age onset 11.7 ± 8.3 years). Eighteen patients had a frontal lobe focus and 72 had a temporal lobe focus (43 mesial; 29 neocortical). Subjects performed an auditory word definition language paradigm using 3 Tesla blood oxygen level dependent (BOLD) EPI functional magnetic resonance imaging (fMRI). Data were analyzed in SPM2. Regional laterality indices (LIs) for inferior frontal gyrus (IFG), and Wernicke’s area (WA), were calculated using a bootstrap method. Categorical language dominance and mean LI were analyzed. Key Findings: Mean WA LI was lower for subjects with a mesial temporal focus compared with a frontal focus (p = 0.04). There was a greater proportion of atypical language in WA for subjects with a mesial temporal focus compared with a frontal focus (χ² = 4.37, p = 0.04). WA LI did not differ for subjects with a neocortical focus compared with a mesial focus or a frontal focus. Mean IFG LI and proportion of atypical language in IFG were similar across seizure focus groups. Age and age of onset were not correlated with mean laterality in WA or IFG. Epilepsy duration tended to be negatively correlated with WA LI (r = ?0.18, p = 0.10), but not IFG LI. Significance: Temporal lobe foci have wide‐ranging effects on the distributed language system. In contrast, the effects of a frontal lobe focus appear restricted to anterior rather than posterior language processing areas.     

Functional MR evaluation of temporal and frontal language dominance compared with the Wada test

OBJECTIVE: To evaluate the reliability of temporal and frontal functional MRI (fMRI) activation for the assessment of language dominance, as compared with the Wada test. PATIENTS AND METHODS: Ten patients with temporal lobe epilepsy were studied using blood oxygen level dependent fMRI and echoplanar imaging (1.5-T). Three tasks were used: semantic verbal fluency, covert sentence repetition, and story listening. Data were analyzed using pixel by pixel autocorrelation and cross-correlation. fMRI laterality indices were defined for several regions of interest as the ratio (L - R)/(L + R), L being the number of activated voxels in the left hemisphere and R in the right hemisphere. Wada laterality indices were defined as the difference in the percentages of errors in language tests between left and right carotid injections. RESULTS: Semantic verbal fluency: The asymmetry of frontal activation was correlated with Wada laterality indices. The strongest correlation was observed in the precentral/middle frontal gyrus/inferior frontal sulcus area. Story listening: The asymmetry of frontal, but not temporal, activation was correlated with Wada laterality indices. Covert sentence repetition: No correlation was observed. CONCLUSIONS: There was a good congruence between hemispheric dominance for language as assessed with the Wada test and fMRI laterality indices in the frontal but not in the temporal lobes. The story listening and the covert sentence repetition tasks increased the sensitivity of detection of posterior language sites that may be useful for brain lesion surgery.     

Functional MRI reveals an interhemispheric dissociation of frontal and temporal language regions in a patient with focal epilepsy

We report the case of a patient with frontal lobe epilepsy in whom the Wada test failed to lateralize representation of language (fluent speech was observed after amobarbital injection on both the right and left side). Functional magnetic resonance imaging (fMRI) during a lexical processing task revealed an atypical organization of language represented by an interhemispheric dissociation of language regions with a right frontal dominance and a left temporal dominance. Consistent with the fMRI results, the patient's ability to name pictures was not reliably impaired by electrocortical stimulation (ECS) of left frontal cortex. The findings from Wada, fMRI, and ECS were confirmed by a lack of language impairment after left frontal lobectomy for seizures. This case illustrates that fMRI can precisely map cortical language networks in epileptic patients and that fMRI may be used to help interpret laterality results provided by the Wada procedure.