Left‐handed musicians show a higher probability of atypical cerebral dominance for language

Music processing and right hemispheric language lateralization share a common network in the right auditory cortex and its frontal connections. Given that the development of hemispheric language dominance takes place over several years, this study tested whether musicianship could increase the probability of observing right language dominance in left‐handers. Using a classic fMRI language paradigm, results showed that atypical lateralization was more predominant in musicians (40%) than in nonmusicians (5%). Comparison of left‐handers with typical left and atypical right lateralization revealed that: (a) atypical cases presented a thicker right pars triangularis and more gyrified left Heschl's gyrus; and (b) the right pars triangularis of atypical cases showed a stronger intra‐hemispheric functional connectivity with the right angular gyrus, but a weaker interhemispheric functional connectivity with part of the left Broca's area. Thus, musicianship is the first known factor related to a higher prevalence of atypical language dominance in healthy left‐handed individuals. We suggest that differences in the frontal and temporal cortex might act as shared predisposing factors to both musicianship and atypical language lateralization.     

Language lateralization in left-handed and ambidextrous people: fMRI data

BACKGROUND: It is generally accepted that most people have left-hemispheric language dominance, though the actual incidence of atypical language distribution in non-right-handed subjects has not been extensively studied. The authors examined language distribution in these subjects and evaluated the relationships between personal handedness, family history of sinistrality, and a language laterality index (LI) measured with fMRI. METHODS: The authors used whole-brain fMRI to examine 50 healthy, non-right-handed subjects (Edinburgh Handedness Inventory quotient between -100 and 52) while they performed language activation and nonlinguistic control tasks. Counts of active voxels (p < 0.001) were computed in 22 regions of interest (ROI) covering both hemispheres and the cerebellum. LI were calculated for each ROI and each entire hemisphere using the formula [L - R]/[L + R]. RESULTS: Activation was predominantly right hemispheric in 8% (4/50), symmetric in 14% (7/50), and predominantly left hemispheric in 78% (39/50) of the subjects. Lateralization patterns were similar for all hemispheric ROI. Associations were observed between personal handedness and LI (r = 0.28, p = 0.046), family history of sinistrality and LI (p = 0.031), and age and LI (r = -0.49, p < 0.001). CONCLUSIONS: The incidence of atypical language lateralization in normal left-handed and ambidextrous subjects is higher than in normal right-handed subjects (22% vs 4-6%). These whole-brain results confirm previous findings in a left-handed cohort studied with fMRI of the lateral frontal lobe. Associations observed between personal handedness and LI and family history of handedness and LI may indicate a common genetic factor underlying the inheritance of handedness and language lateralization.     

Atypically rightward cerebral asymmetry in male adults with autism stratifies individuals with and without language delay

In humans, both language and fine motor skills are associated with left‐hemisphere specialization, whereas visuospatial skills are associated with right‐hemisphere specialization. Individuals with autism spectrum conditions (ASC) show a profile of deficits and strengths that involves these lateralized cognitive functions. Here we test the hypothesis that regions implicated in these functions are atypically rightward lateralized in individuals with ASC and, that such atypicality is associated with functional performance. Participants included 67 male, right‐handed adults with ASC and 69 age‐ and IQ‐matched neurotypical males. We assessed group differences in structural asymmetries in cortical regions of interest with voxel‐based analysis of grey matter volumes, followed by correlational analyses with measures of language, motor and visuospatial skills. We found stronger rightward lateralization within the inferior parietal lobule and reduced leftward lateralization extending along the auditory cortex comprising the planum temporale, Heschl's gyrus, posterior supramarginal gyrus, and parietal operculum, which was more pronounced in ASC individuals with delayed language onset compared to those without. Planned correlational analyses showed that for individuals with ASC, reduced leftward asymmetry in the auditory region was associated with more childhood social reciprocity difficulties. We conclude that atypical cerebral structural asymmetry is a potential candidate neurophenotype of ASC. Hum Brain Mapp 37:230–253, 2016. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.     

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.     

Correlation between language organization and diffusion tensor abnormalities in refractory partial epilepsy

PURPOSE: Atypical language organization is more frequently found in patients with refractory partial epilepsy than in healthy controls; however, the reasons for this are not well known. Here we assess the relation between language laterality index (LI) and white-matter tract changes. METHODS: Nine patients with refractory partial epilepsy were assessed with a 3-T GE scanner. Functional magnetic resonance imaging (fMRI) of language and diffusion tensor imaging (DTI) were acquired. For the fMRI, a noun-verb generation task was performed, all images were motion corrected, and activated pixels in classic language areas were counted. The DTI images were acquired in six standard directions with an initial non-diffusion-weighted scan. The "average anisotropy" was determined in a region of interest in the frontal lobe, temporal lobe, and parietal lobe white matter. An asymmetry index (AI) was calculated for language and DTI. Atypical language lateralization was diagnosed if the lateralization index (LI)-language was smaller than 0.4. RESULTS: Two of the nine patients had atypical language localization (LI-language, -0.6, and 0.3); both had left temporal DTI asymmetry (LI-DTI, -0.3 and -0.2). The remaining seven patients had typical language localization, and no marked DTI abnormalities. Asymmetry in temporal lobe DTI correlated with LI-language (r= 0.8; p = 0.006). CONCLUSIONS: Atypical language lateralization in patients with partial epilepsy may be associated with white-matter tract abnormalities.     

Language lateralization from task‐based and resting state functional MRI in patients with epilepsy

We compared resting state (RS) functional connectivity and task‐based fMRI to lateralize language dominance in 30 epilepsy patients (mean age = 33; SD = 11; 12 female), a measure used for presurgical planning. Language laterality index (LI) was calculated from task fMRI in frontal, temporal, and frontal + temporal regional masks using LI bootstrap method from SPM12. RS language LI was assessed using two novel methods of calculating RS language LI from bilateral Broca's area seed based connectivity maps across regional masks and multiple thresholds (p < .05, p < .01, p < .001, top 10% connections). We compared LI from task and RS fMRI continuous values and dominance classifications. We found significant positive correlations between task LI and RS LI when functional connectivity thresholds were set to the top 10% of connections. Concordance of dominance classifications ranged from 20% to 30% for the intrahemispheric resting state LI method and 50% to 63% for the resting state LI intra‐ minus interhemispheric difference method. Approximately 40% of patients left dominant on task showed RS bilateral dominance. There was no difference in LI concordance between patients with right‐sided and left‐sided resections. Early seizure onset (<6 years old) was not associated with atypical language dominance during task‐based or RS fMRI. While a relationship between task LI and RS LI exists in patients with epilepsy, language dominance is less lateralized on RS than task fMRI. Concordance of language dominance classifications between task and resting state fMRI depends on brain regions surveyed and RS LI calculation method.     

FMRI lateralization of expressive language in children with cerebral lesions

PURPOSE: Lateralization of language function is crucial to the planning of surgery in children with frontal or temporal lobe lesions. We examined the utility of functional magnetic resonance imaging (fMRI) as a determinant of lateralization of expressive language in children with cerebral lesions. METHODS: fMRI language lateralization was attempted in 35 children (29 with epilepsy) aged 8-18 years with frontal or temporal lobe lesions (28 left hemisphere, five right hemisphere, two bilateral). Axial and coronal fMRI scans through the frontal and temporal lobes were acquired at 1.5 Tesla by using a block-design, covert word-generation paradigm. Activation maps were lateralized by blinded visual inspection and quantitative asymmetry indices (hemispheric and inferior frontal regions of interest, at p<0.001 uncorrected and p<0.05 Bonferroni corrected). RESULTS: Thirty children showed significant activation in the inferior frontal gyrus. Lateralization by visual inspection was left in 21, right in six, and bilateral in three, and concordant with hemispheric and inferior frontal quantitative lateralization in 93% of cases. Developmental tumors and dysplasias involving the inferior left frontal lobe had activation overlying or abutting the lesion in five of six cases. fMRI language lateralization was corroborated in six children by frontal cortex stimulation or intracarotid amytal testing and indirectly supported by aphasiology in a further six cases. In two children, fMRI language lateralization was bilateral, and corroborative methods of language lateralization were left. Neither lesion lateralization, patient handedness, nor developmental versus acquired nature of the lesion was associated with language lateralization. Involvement of the left inferior or middle frontal gyri increased the likelihood of atypical language lateralization. CONCLUSIONS: fMRI lateralizes language in children with cerebral lesions, although caution is needed in interpretation of individual results.     

Cerebral lateralization of praxis in right- and left-handedness: same pattern, different strength

We aimed to investigate the effect of hand effector and handedness on the cerebral lateralization of pantomiming learned movements. Fourteen right-handed and 14 left-handed volunteers performed unimanual and bimanual tool-use pantomimes with their dominant or nondominant hand during fMRI. A left hemispheric lateralization was observed in the right- and left-handed group regardless of which hand(s) performed the task. Asymmetry was most marked in the dorsolateral prefrontal cortex (DLPFC), premotor cortex (PMC), and superior and inferior parietal lobules (SPL and IPL). Unimanual pantomimes did not reveal any significant differences in asymmetric cerebral activation patterns between left- and right-handers. Bimanual pantomimes showed increased left premotor and posterior parietal activation in left- and right-handers. Lateralization indices (LI) of the 10% most active voxels in DLPFC, PMC, SPL, and IPL were calculated for each individual in a contrast that compared all tool versus all control conditions. Left-handers showed a significantly reduced overall LI compared with right-handers. This was mainly due to diminished asymmetry in the IPL and SPL. We conclude that the recollection and pantomiming of learned gestures recruits a similar left lateralized activation pattern in right and left-handed individuals. Handedness only influences the strength (not the side) of the lateralization, with left-handers showing a reduced degree of asymmetry that is most readily observed over the posterior parietal region. Together with similar findings in language and visual processing, these results point to a lesser hemispheric specialization in left-handers that may be considered in the cost/benefit assessment to explain the disproportionate handedness polymorphism in humans.     

Language lateralization in left-handed patients with schizophrenia

We evaluated hemispheric lateralization of language production in non-right-handed (NRH) patients with schizophrenia compared with matched right-handed (RH) patients, NRH control, and RH control subjects. First, the ability to generate verbs during overt training trials was checked in 78 subjects. They were then evaluated with functional magnetic resonance imaging (fMRI) while performing a covert verb generation task. No significant interactions between illness and handedness and no illness effect were observed in functional asymmetry. There was significantly less leftward asymmetry of the inferior frontal, precentral, and supramarginal gyri as well as the intra-parietal sulcus in non-right-handers compared to right-handers taking into account the task performances. Our findings suggested that decreased lateralization for language production was more closely related to handedness than to schizophrenia.     

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.     

fMRI shows atypical language lateralization in pediatric epilepsy patients

PURPOSE: The goal of this study was to compare language lateralization between pediatric epilepsy patients and healthy children. METHODS: Two groups of subjects were evaluated with functional magnetic resonance imaging (fMRI) by using a silent verb-generation task. The first group included 18 pediatric epilepsy patients, whereas the control group consisted of 18 age/gender/handedness-matched healthy subjects. RESULTS: A significant difference in hemispheric lateralization index (LI) was found between children with epilepsy (mean LI =-0.038) and the age/gender/handedness-matched healthy control subjects (mean LI=0.257; t=6.490, p<0.0001). A dramatic difference also was observed in the percentage of children with epilepsy (77.78%) who had atypical LI (right-hemispheric or bilateral, LI<0.1) when compared with the age/gender/handedness-matched group (11.11%; chi(2)=16.02, p<0.001). A linear regression analysis showed a trend toward increasing language lateralization with age in healthy controls (R(2)=0.152; p=0.108). This association was not observed in pediatric epilepsy subjects (R(2)=0.004, p=0.80). A significant association between language LI and epilepsy duration also was found (R(2)=0.234, p<0.05). CONCLUSIONS: This study shows that epilepsy during childhood is associated with neuroplasticity and reorganization of language function.     

Comprehensive presurgical functional MRI language evaluation in adult patients with epilepsy

Functional magnetic resonance imaging (fMRI) has the potential to replace the intracarotid amobarbital procedure (IAP) in presurgical evaluation of patients with epilepsy. In this study, we compared fMRI verb generation (VG) and semantic decision/tone decision (SDTD) tasks and the IAP in their ability to localize language functions in patients with epilepsy undergoing presurgical evaluation. We enrolled 50 healthy controls to establish normal language activation patterns for VG and SDTD tasks at 3 or 4 T, and to design language regions of interest (ROIs) that were later applied to 38 patients with epilepsy (28 of 38 also underwent the IAP). We calculated laterality indices (LIs) for each task for each subject based on the ROIs, and we used general linear modeling to analyze the fMRI data. All healthy and epileptic subjects activated language areas with both fMRI tasks. We found significant correlations in language lateralization between the fMRI tasks (r=0.495, P<0.001) and between VG and IAP (r=0.652, P<0.001) and SDTD and IAP (r=0.735, P<0.001). The differences in LIs between SDTD and VG tasks were small and not affected by age, gender, epilepsy status, handedness, or performance. SDTD and VG tasks combined explained approximately 58.4% in the variability of the IAP/language. In the general linear modeling, only the SDTD task significantly contributed to the determination of language lateralization in patients with epilepsy undergoing presurgical evaluation. Results indicate a moderate convergent validity between both fMRI language tasks and between IAP and fMRI tasks. The results of this study indicate that either of these fMRI tasks can be used for language lateralization in patients with epilepsy undergoing presurgical evaluation, but that the SDTD task is likely to provide more information regarding language lateralization than the VG task.     

Strengthening of laterality of verbal and visuospatial functions during childhood and adolescence

Cognitive functions in the child's brain develop in the context of complex adaptive processes, determined by genetic and environmental factors. Little is known about the cerebral representation of cognitive functions during development. In particular, knowledge about the development of right hemispheric (RH) functions is scarce. Considering the dynamics of brain development, localization and lateralization of cognitive functions must be expected to change with age. Twenty healthy subjects (8.6-20.5 years) were examined with fMRI and neuropsychological tests. All participants completed two fMRI tasks known to activate left hemispheric (LH) regions (language tasks) and two tasks known to involve predominantly RH areas (visual search tasks). A laterality index (LI) was computed to determine the asymmetry of activation. Group analysis revealed unilateral activation of the LH language circuitry during language tasks while visual search tasks induced a more widespread RH activation pattern in frontal, superior temporal, and occipital areas. Laterality of language increased between the ages of 8-20 in frontal (r = 0.392, P = 0.049) and temporal (r = 0.387, P = 0.051) areas. The asymmetry of visual search functions increased in frontal (r = -0.525, P = 0.009) and parietal (r = -0.439, P = 0.027) regions. A positive correlation was found between Verbal-IQ and the LI during a language task (r = 0.585, P = 0.028), while visuospatial skills correlated with LIs of visual search (r = -0.621, P = 0.018). To summarize, cognitive development is accompanied by changes in the functional representation of neuronal circuitries, with a strengthening of lateralization not only for LH but also for RH functions. Our data show that age and performance, independently, account for the increases of laterality with age.     

Material specific lateralization of medial temporal lobe function: An fMRI investigation

The theory of material specific lateralization of memory function posits that left and right MTL regions are asymmetrically involved in mnemonic processing of verbal and nonverbal material respectively. Lesion and functional imaging (fMRI) studies provide robust evidence for a left MTL asymmetry in the verbal memory domain. Evidence for a right MTL/nonverbal asymmetry is not as robust. A handful of fMRI studies have investigated this issue but have generally utilised nonverbal stimuli which are amenable to semantic elaboration. This fMRI study aimed to investigate the neural correlates of recognition memory processing in 20 healthy young adults (mean age = 26 years) for verbal stimuli and nonverbal stimuli that were specifically designed to minimize verbalisation. Analyses revealed that the neural correlates of recognition memory processing for verbal and nonverbal stimuli were differentiable and asymmetrically recruited the left and right MTL respectively. The right perirhinal cortex and hippocampus were preferentially involved in successful recognition memory of items devoid of semantic information. In contrast, the left anterior hippocampus was preferentially involved in successful recognition memory of stimuli which contained semantic meaning. These results suggest that the left MTL is preferentially involved in mnemonic processing of verbal/semantic information. In contrast, the right MTL is preferentially involved in visual/non‐semantic mnemonic processing. We propose that during development, the left MTL becomes specialised for verbal mnemonic processing due to its proximity with left lateralised cortical language processing areas while visual/non‐semantic mnemonic processing gets ‘crowded out’ to become predominantly, but not completely, the domain of the right MTL. Hum Brain Mapp 37:933–941, 2016. © 2015 Wiley Periodicals, Inc .     

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.     

Regional differences in the developmental trajectory of lateralization of the language network

The timing and developmental factors underlying the establishment of language dominance are poorly understood. We investigated the degree of lateralization of traditional frontotemporal and modulatory prefrontal‐cerebellar regions of the distributed language network in children (n = 57) ages 4 to 12—a critical period for language consolidation. We examined the relationship between the strength of language lateralization and neuropsychological measures and task performance. The fundamental language network is established by four with ongoing maturation of language functions as evidenced by strengthening of lateralization in the traditional frontotemporal language regions; temporal regions were strongly and consistently lateralized by age seven, while frontal regions had greater variability and were less strongly lateralized through age 10. In contrast, the modulatory prefrontal‐cerebellar regions were the least strongly lateralized and degree of lateralization was not associated with age. Stronger core language skills were significantly correlated with greater right lateralization in the cerebellum. Hum Brain Mapp 35:270–284, 2014. © 2012 Wiley Periodicals, Inc.     

Lateralization of the arcuate fasciculus from childhood to adulthood and its relation to cognitive abilities in children

The arcuate fasciculus is a major white matter tract involved in language processing that has also been repeatedly implicated in intelligence and reasoning tasks. Language in the human brain is lateralized in terms of both function and structure, and while the arcuate fasciculus reflects this asymmetry, its pattern of lateralization is poorly understood in children and adolescents. We used diffusion tensor imaging (DTI) and tractography to examine arcuate fasciculus lateralization in a large (n = 183) group of healthy right‐handed volunteers aged 5–30 years; a subset of 68 children aged 5–13 years also underwent cognitive assessments. Fractional anisotropy and number of streamlines of the arcuate fasciculus were both significantly higher in the left hemisphere than the right hemisphere in most subjects, although some subjects (10%) were right lateralized. Age and gender effects on lateralization were not significant. Children receiving cognitive assessments were divided into three groups: a “left‐only” group in whom only the left side of the arcuate fasciculus could be tracked, a left‐lateralized group, and a right‐lateralized group. Scores on the Peabody Picture Vocabulary Test (PPVT) and NEPSY Phonological Processing task differed significantly among groups, with left‐only subjects outperforming the right‐lateralized group on the PPVT, and the left‐lateralized children scoring significantly better than the right‐lateralized group on phonological processing. In summary, DTI tractography demonstrates leftward arcuate fasciculus lateralization in children, adolescents, and young adults, and reveals a relationship between structural white matter lateralization and specific cognitive abilities in children. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Language lateralization in temporal lobe epilepsy: a comparison between fMRI and the Wada Test

PURPOSE: Recent studies have claimed that language functional magnetic resonance imaging (fMRI) can identify language lateralization in patients with temporal lobe epilepsy (TLE) and that fMRI-based findings are highly concordant with the conventional assessment procedure of speech dominance, the intracarotid amobarbital test (IAT). METHODS: To establish the power of language fMRI to detect language lateralization during presurgical assessment, we compared the findings of a semantic decision paradigm with the results of a standard IAT in 68 patients with chronic intractable right and left temporal lobe epilepsy (rTLE, n=28; lTLE, n=40) who consecutively underwent a presurgical evaluation program. The patient group also included 14 (20.6%) subjects with atypical (bilateral or right hemisphere) speech. Four raters used a visual analysis procedure to determine the laterality of speech-related activation individually for each patient. RESULTS: Overall congruence between fMRI-based laterality and the laterality quotient of the IAT was 89.3% in rTLE and 72.5% in lTLE patients. Concordance was best in rTLE patients with left speech. In lTLE patients, language fMRI identified atypical, right hemisphere speech dominance in every case, but missed left hemisphere speech dominance in 17.2%. Frontal activations had higher concordance with the IAT than did activations in temporoparietal or combined regions of interest (ROIs). Because of methodologic problems, recognition of bilateral speech was difficult. CONCLUSIONS: These data provide evidence that language fMRI as used in the present study has limited correlation with the IAT, especially in patients with lTLE and with mixed speech dominance. Further refinements regarding the paradigms and analysis procedures will be needed to improve the contribution of language fMRI for presurgical assessment.     

Is Language Lateralization in Temporal Lobe Epilepsy Patients Related to the Nature of the Epileptogenic Lesion?

PURPOSE: Early acquired lesions are considered to be a risk factor for atypical language lateralization in epilepsy, whereas developmental lesions are not. Hippocampal sclerosis (HS) can be understood as an early, acquired lesion, whereas developmental tumors (DT) are thought to originate in utero. We assessed whether language lateralization differs between these groups of temporal lobe epilepsy patients. METHODS: We used 3-Tesla functional MRI (fMRI) to assess 41 patients (16 DT, 25 HS) and 50 controls, performing a noun-verb-generation task. fMRI data were processed by using SPM2. A laterality index (LI) was calculated based on the number of activated voxels in left- and right-sided frontal lobe language areas. Atypical lateralization was considered if the index was < or = 0.2. RESULTS: Patients had a lower LI (0.42 +/- 0.5) than controls (0.6 +/- 0.3; p < or = 0.05), but the LI was not different between DT (0.44 +/- 0.5) and HS patients (0.43 +/- 0.4; p = 0.9). The frequency of atypical lateralization was increased in patients (27%) compared with controls (8%) but was similar in both patient groups (DT, 31%; HS, 24%). HS patients had an earlier onset and longer duration of epilepsy and a higher frequency of significant antecedent events (p < or = 0.05). CONCLUSIONS: Patients with TLE demonstrate a deviation toward atypical language lateralization. However, language lateralization was not different between patients with presumably acquired lesions compared with patients with developmental pathology. This suggests that the nature of the temporal lobe lesion does not influence overall language lateralization.