Lateralization Of Language Functions Research Articles

Atypical lateralization of visuospatial attention can be associated with better or worse performance on line bisection.

The causal and statistical hypotheses diverge in determining whether the lateralization of language function in one cerebral hemisphere entails the lateralization of visuospatial function in the opposite hemisphere. Additionally, it remains unclear if the atypical segregation of these functions could influence cognitive performance. This study addresses these questions by examining the hemispheric lateralization of visuospatial attention during a line bisection judgement (landmark) task in three groups of healthy non-right-handed individuals with different language production segregations: left (typical), ambilateral (atypical), and right (atypical). Consistent with the causal hypothesis, results indicate that the groups with left and right language lateralization primarily utilize the opposite hemisphere for visuospatial attention. The ambilateral group, however, displays a pattern compatible with an independent segregation, supporting the statistical hypothesis. Behavioral analyses reveal that atypical lateralization of visuospatial attention (non-right) can lead to either better or worse performance during the landmark task, depending on the specific pattern. Bilateral organization is associated with reduced overall accuracy, whereas the left segregation results in improved performance during the most challenging trials. These findings suggest the existence of diverse pathways to lateralization, akin to either the causal or statistical hypothesis, which can result in cognitive advantages or disadvantages.

Diffusion magnetic resonance imaging connectome features are predictive of functional lateralization of semantic processing in the anterior temporal lobes.

Assessment of regional language lateralization is crucial in many scenarios, but not all populations are suited for its evaluation via task-functional magnetic resonance imaging (fMRI). In this study, the utility of structural connectome features for the classification of language lateralization in the anterior temporal lobes (ATLs) was investigated. Laterality indices for semantic processing in the ATL were computed from task-fMRI in 1038 subjects from the Human Connectome Project who were labeled as stronger rightward lateralized (RL) or stronger leftward to bilaterally lateralized (LL) in a data-driven approach. Data of unrelated subjects (n= 432) were used for further analyses. Structural connectomes were generated from diffusion-MRI tractography, and graph theoretical metrics (node degree, betweenness centrality) were computed. A neural network (NN) and a random forest (RF) classifier were trained on these metrics to classify subjects as RL or LL. After classification, comparisons of network measures were conducted via permutation testing. Degree-based classifiers produced significant above-chance predictions both during cross-validation (NN: AUC-ROC[CI]=0.68[0.64-0.73], accuracy[CI]=68.34%[63-73.2%]; RF: AUC-ROC[CI]=0.7[0.66-0.73], accuracy[CI]=64.81%[60.9-68.5]) and testing (NN: AUC-ROC[CI]=0.69[0.53-0.84], accuracy[CI]=68.09[53.2-80.9]; RF: AUC-ROC[CI]=0.68[0.53-0.84], accuracy[CI]=68.09[55.3-80.9]). Comparison of network metrics revealed small effects of increased node degree within the right posterior middle temporal gyrus (pMTG) in subjects with RL, while degree was decreased in the right posterior cingulate cortex (PCC). Above-chance predictions of functional language lateralization in the ATL are possible based on diffusion-MRI connectomes alone. Increased degree within the right pMTG as a right-sided homologue of a known semantic hub, and decreased hubness of the right PCC may form a structural basis for rightward-lateralized semantic processing.

Multilingual Aphasia

Multilingual aphasia is synonymous with polyglot aphasia and is often indistinguishable from bilingual aphasia. Multilingual aphasia, including bilingual aphasia, has been of interest from the perspectives of impairment and recovery patterns in each language, factors involved in recovery, and variations in cerebral lateralization of language function in each language. Early premorbid language proficiency and language use have been shown to play a crucial role in the manifestation of bilingual aphasia. Paradis (1989) classified the recovery pattern from bilingual aphasia into nine patterns and demonstrated that multiple variables, including age of language acquisition and language proficiency are involved in multiple dimensions. Previous studies on crossed aphasia have suggested the involvement of the right hemisphere in the cerebral lateralization of language function. However, a subsequent meta-analysis demonstrated that early bilingual individuals who acquired both languages by the age of 6 years had a bilateral organization of both languages. In contrast, late bilingual and monolingual individuals who acquired a second language after the age of 6 years had the lateralization of language function in the left hemisphere for both languages.

Heritability of language laterality assessed by functional transcranial Doppler ultrasound: a twin study.

Background: Prior studies have estimated heritability of around 0.25 for the trait of handedness, with studies of structural brain asymmetry giving estimates in a similar or lower range. Little is known about heritability of functional language lateralization. This report describes heritability estimates using functional language laterality and handedness phenotypes in a twin sample previously reported by Wilson and Bishop (2018). Methods: The total sample consisted of 194 twin pairs (49% monozygotic) aged from 6 to 11 years. A language laterality index was obtained for 141 twin pairs, who completed a protocol where relative blood flow through left and right middle cerebral arteries was measured using functional transcranial Doppler ultrasound (fTCD) while the child described animation sequences. Handedness data was available from the Edinburgh Handedness Inventory (EHI) and Quantification of Hand Preference (QHP) for all 194 pairs. Heritability was assessed using conventional structural equation modeling, assuming no effect of shared environment (AE model). Results: For the two handedness measures, heritability estimates (95% CI) were consistent with prior research: .25 (.03 - .34) and .18 (0 - .31) respectively for the EHI and QHP. For the language laterality index, however, the twin-cotwin correlations were close to zero for both MZ and DZ twins, and the heritability estimate was zero (0 - .15). Conclusions: A single study cannot rule out a genetic effect on language lateralisation. It is possible that the low twin-cotwin correlations were affected by noisy data: although the split-half reliability of the fTCD-based laterality index was high (0.85), we did not have information on test-retest reliability in children, which is likely to be lower. We cannot reject the hypothesis that there is low but nonzero heritability for this trait, but our data suggest that individual variation in language lateralisation is predominantly due to stochastic variation in neurodevelopment.

Correlation of language lateralization with resting state hippocampal connectivity in temporal lobe epilepsy patients

Background/aimThe main purpose of this study is to evaluate the resting state hippocampal connectivity with language areas and to correlate them with laterality index calculations on single subject basis, hence to present hippocampal lateralization for language with rs-fMRI.Materials and methodsTask based and rs-fMRI data were gathered from a total of 45 subjects in 3T scanner. BrainVoyager QX, SPM, and CONN softwares were used for data analysis. LI score of each subject was calculated and converted into normalized LI score (nLI). Intrahemispheric rs-connectivity analysis was performed between hippocampus and Broca’s regions on both sides. Correlation between these variables was measured with SPSS software.ResultsRight-TLE patients were found to have highest whereas left-TLE group were found to have lowest mean LI scores. Regarding hippocampal-lingual networks; left intrahemispheric connectivity values showed strong positive correlation with nLI values in left, right-TLE patients and healthy controls (P = 0.035, 0.014, 0.047). There were no significant correlation between right intrahemispheric connectivity values and nLI scores in all groups.ConclusionThis study seems to depict the existence of resting state hippocampal-lingual functional network which correlates well with lateralization of language function in the left hemisphere in both temporal lobe epilepsy patients and healthy controls.

Heritability of language laterality assessed by functional transcranial Doppler ultrasound: a twin study.

Background: Prior studies have estimated heritability of around 0.25 for the trait of handedness, with studies of structural brain asymmetry giving estimates in a similar or lower range. Little is known about heritability of functional language lateralization. This report describes heritability estimates using functional language laterality and handedness phenotypes in a twin sample previously reported by Wilson and Bishop (2018). Methods: The total sample consisted of 194 twin pairs (49% monozygotic) aged from 6 to 11 years. A language laterality index was obtained for 141 twin pairs, who completed a protocol where relative blood flow through left and right middle cerebral arteries was measured using functional transcranial Doppler ultrasound (fTCD) while the child described animation sequences. Handedness data was available from the Edinburgh Handedness Inventory (EHI) and Quantification of Hand Preference (QHP) for all 194 pairs. Heritability was assessed using conventional structural equation modeling, assuming no effect of shared environment (AE model). Results: For the two handedness measures, heritability estimates were consistent with prior research: 0.23 and 0.22 respectively for the EHI and QHP. For the language laterality index, however, the twin-cotwin correlations were close to zero for both MZ and DZ twins, and the heritability estimate was zero. Conclusions: A single study cannot rule out a genetic effect on language lateralisation. It is possible that the low twin-cotwin correlations were affected by noisy data: although the split-half reliability of the fTCD-based laterality index was high (0.85), we did not have information on test-retest reliability in children, which is likely to be lower. We cannot reject the hypothesis that there is low but nonzero heritability for this trait, but our data suggest that individual variation in language lateralisation is predominantly due to stochastic variation in neurodevelopment.

Peer Review Report For: Negligible heritability of language laterality assessed by functional transcranial Doppler ultrasound: a twin study [version 1; peer review: 1 approved with reservations]. Wellcome Open Research 2019, 4:161

Background: Prior studies have estimated heritability of around 0.25 for the trait of handedness, with studies of structural brain asymmetry giving estimates in a similar or lower range. Little is known about heritability of functional language lateralization. This report describes heritability estimates using functional language laterality and handedness phenotypes in a twin sample previously reported by Wilson and Bishop (2018). Methods: The total sample consisted of 194 twin pairs (49% monozygotic) aged from 6 to 11 years. A language laterality index was obtained for 141 twin pairs, who completed a protocol where relative blood flow through left and right middle cerebral arteries was measured using functional transcranial Doppler ultrasound (fTCD) while the child described animation sequences. Handedness data was available from the Edinburgh Handedness Inventory (EHI) and Quantification of Hand Preference (QHP) for all 194 pairs. Heritability was assessed using conventional structural equation modeling, assuming no effect of shared environment (AE model). Results: For the two handedness measures, heritability estimates (95% CI) were consistent with prior research: .25 (.03 - .34) and .18 (0 – .31) respectively for the EHI and QHP. For the language laterality index, however, the twin-cotwin correlations were close to zero for both MZ and DZ twins, and the heritability estimate was zero (0 - .15). Conclusions: A single study cannot rule out a genetic effect on language lateralisation. It is possible that the low twin-cotwin correlations were affected by noisy data: although the split-half reliability of the fTCD-based laterality index was high (0.85), we did not have information on test-retest reliability in children, which is likely to be lower. We cannot reject the hypothesis that there is low but nonzero heritability for this trait, but our data suggest that individual variation in language lateralisation is predominantly due to stochastic variation in neurodevelopment.

Sex Difference in Language Processing in Patients With Malignant Brain Tumors

Abstract INTRODUCTION Numerous differences between males and females in brain organization have been described including in the development, performance, and lateralization of language function. However, there is very limited knowledge of whether language processing differs across sex in patients with brain lesions. In particular, malignant brain tumors (MBT) demonstrate significant sex differences in incidence and long-term survival. Given the importance of brain organization and planning surgical treatment for patients with brain tumors, we investigated the effect of sex on the organization of language in a cohort of patients with MBT. METHODS In the current study, we carried out a retrospective analysis in 47 patients with MBT (22 females, 25 males), retrieving their clinical characteristics and task-based and resting-state functional magnetic resonance image (fMRI) data from our clinical database. General Linear Model (GLM) and region-of-interest (ROI) based resting-state functional connectivity (RSFC) analyses were applied to explore the effect of sex on language tasks associated activations and functional connectivity. RESULTS Across the Sentence Completion task and Antonym Generation task, female patients showed greater activation volumes in the left inferior frontal gyrus, right precuneus, and left superior parietal lobule, while male patients showed larger clusters of activation of the left supplemental motor area (SMA), left inferior parietal lobule (IPL), left precuneus, bilateral precentral gyrus, and right supramarginal gyrus (SMG). Furthermore, the left SMA was a highly sex-specific brain area during the language performance, and it showed stronger resting-state correlations with brain areas within the intrinsic language network in females, while it showed stronger resting-state connections with brain areas involving the visuomotor/higher level cognitive functions in males. CONCLUSION These findings enhance our understanding of the role of sex in language organization in patients with MBT, helping neurosurgeons assess surgical risk and plan surgery in patients with MBT to best preserve language function.

Tracing the structural origins of atypical language representation: consequences of prenatal mirror-imaged brain asymmetries in a dizygotic twin couple

We investigated the predictive value of prenatal superior temporal sulcus (STS) depth asymmetry in a special case of a female dizygotic twin that showed inverted prenatal asymmetry of this structure. For this purpose, we performed a follow-up investigation in this former fetus at the age of seven, where we assessed the functional language lateralization using task-based and resting-state functional magnetic resonance imaging (fMRI). As control group we employed her twin brother, who showed a typical folding pattern prenatally, as well as a complementary set of four age-matched children that had fetal MRI of their brains and typical STS depth asymmetry. We could show that the twin with the atypical fetal asymmetry of the STS also showed significantly differing rightward language lateralization in the frontal and temporal lobes. Additionally, resting-state data suggest a stronger connectivity between inferior frontal gyri in this case. The twin showed normal cognitive development. This result gives a first glimpse into the STS’ atypical asymmetry being a very early morphological marker for later language lateralization.

Age-related language lateralization assessed by fMRI: The effects of sex and handedness

Previous studies focusing on the relationship between lateralization of language function and age suffer from lack of a balanced distribution of age and handedness among participants, especially in the extremes of age. This limits our understanding of the influence of these factors on lateralization of language circuitry. The hemispheric asymmetry reduction in older adults (HAROLD) model suggests that under similar circumstances, involvement in cognitive processes of prefrontal (and potentially other) cortical areas tends to be less lateralized with age. In this study, we aimed to investigate the link between age, gender, and language lateralization in a large group of healthy participants with a relatively even distribution of age and handedness in order to further test the HAROLD model. 99 healthy men (33 left-handed; age range 18–74years) and 125 women (44 left-handed; age range 19–76) were recruited. All participants underwent fMRI at 3T with a semantic decision and a verb generation tasks and received a battery of linguistic tests. Lateralization indexes (LI) were calculated for each participant based on fMRI results for each task separately. LIs were found to be significantly decreasing with age only in right-handed men and only in temporo-parietal cortical area. LIs did not change with age in other brain regions or in left-handed subjects. Our results do not support the HAROLD model and suggest a potentially different relationship between aging and lateralization of language functions.

Resting-State Seed-Based Analysis: An Alternative to Task-Based Language fMRI and Its Laterality Index.

Language is a cardinal function that makes human unique. Preservation of language function poses a great challenge for surgeons during resection. The aim of the study was to assess the efficacy of resting-state fMRI in the lateralization of language function in healthy subjects to permit its further testing in patients who are unable to perform task-based fMRI. Eighteen healthy right-handed volunteers were prospectively evaluated with resting-state fMRI and task-based fMRI to assess language networks. The laterality indices of Broca and Wernicke areas were calculated by using task-based fMRI via a voxel-value approach. We adopted seed-based resting-state fMRI connectivity analysis together with parameters such as amplitude of low-frequency fluctuation and fractional amplitude of low-frequency fluctuation (fALFF). Resting-state fMRI connectivity maps for language networks were obtained from Broca and Wernicke areas in both hemispheres. We performed correlation analysis between the laterality index and the z scores of functional connectivity, amplitude of low-frequency fluctuation, and fALFF. Pearson correlation analysis between signals obtained from the z score of fALFF and the laterality index yielded a correlation coefficient of 0.849 (P < .05). Regression analysis of the fALFF with the laterality index yielded an R2 value of 0.721, indicating that 72.1% of the variance in the laterality index of task-based fMRI could be predicted from the fALFF of resting-state fMRI. The present study demonstrates that fALFF can be used as an alternative to task-based fMRI for assessing language laterality. There was a strong positive correlation between the fALFF of the Broca area of resting-state fMRI with the laterality index of task-based fMRI. Furthermore, we demonstrated the efficacy of fALFF for predicting the laterality of task-based fMRI.

Vascular risk factors in Alzheimer disease and mild cognitive impairment

Functional magnetic resonance imaging (fMRI) is a non-invasive pre-surgical tool used to assess localization and lateralization of language function in brain tumor and vascular lesion patients in order to guide neurosurgeons as they devise a surgical approach to treat these lesions. We investigated the effect of varying the statistical thresholds as well as the type of language tasks on functional activation patterns and language lateralization. We hypothesized that language lateralization indices (LIs) would be threshold- and task-dependent.Imaging data were collected from brain tumor patients (n = 67, average age 48 years) and vascular lesion patients (n = 25, average age 43 years) who received pre-operative fMRI scanning. Both patient groups performed expressive (antonym and/or letter-word generation) and receptive (tumor patients performed text-reading; vascular lesion patients performed text-listening) language tasks. A control group (n = 25, average age 45 years) performed the letter-word generation task.Brain tumor patients showed left-lateralization during the antonym-word generation and text-reading tasks at high threshold values and bilateral activation during the letter-word generation task, irrespective of the threshold values. Vascular lesion patients showed left-lateralization during the antonym and letter-word generation, and text-listening tasks at high threshold values.Our results suggest that the type of task and the applied statistical threshold influence LI and that the threshold effects on LI may be task-specific. Thus identifying critical functional regions and computing LIs should be conducted on an individual subject basis, using a continuum of threshold values with different tasks to provide the most accurate information for surgical planning to minimize post-operative language deficits.

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

Background and purposeFunctional magnetic resonance imaging (fMRI) is a non-invasive pre-surgical tool used to assess localization and lateralization of language function in brain tumor and vascular lesion patients in order to guide neurosurgeons as they devise a surgical approach to treat these lesions. We investigated the effect of varying the statistical thresholds as well as the type of language tasks on functional activation patterns and language lateralization. We hypothesized that language lateralization indices (LIs) would be threshold- and task-dependent.Materials and methodsImaging data were collected from brain tumor patients (n = 67, average age 48 years) and vascular lesion patients (n = 25, average age 43 years) who received pre-operative fMRI scanning. Both patient groups performed expressive (antonym and/or letter-word generation) and receptive (tumor patients performed text-reading; vascular lesion patients performed text-listening) language tasks. A control group (n = 25, average age 45 years) performed the letter-word generation task.ResultsBrain tumor patients showed left-lateralization during the antonym-word generation and text-reading tasks at high threshold values and bilateral activation during the letter-word generation task, irrespective of the threshold values. Vascular lesion patients showed left-lateralization during the antonym and letter-word generation, and text-listening tasks at high threshold values.ConclusionOur results suggest that the type of task and the applied statistical threshold influence LI and that the threshold effects on LI may be task-specific. Thus identifying critical functional regions and computing LIs should be conducted on an individual subject basis, using a continuum of threshold values with different tasks to provide the most accurate information for surgical planning to minimize post-operative language deficits.

From structure to function in the lateralized brain: How structural properties of the arcuate and uncinate fasciculus are associated with dichotic listening performance

Structural asymmetries in white matter tracts within the language system have been suggested to be one of the factors underlying functional language lateralization. To test this assumption, the present study examined how performance in the dichotic listening task, a behavioral measure of language dominance, is affected by macro- and microstructural properties of the arcuate and uncinate fasciculus. To this end, whole brain tractography was performed on 29 diffusion tensor imaging datasets obtained from healthy adult participants. Mean tract volume and fractional anisotropy of the uncinate and arcuate fasciculus were linked to the individual extent of the right ear advantage in the dichotic listening task. On the macrostructural level, both arcuate and uncinate fasciculus had a larger tract volume in the left compared to the right hemisphere. In contrast, fractional anisotropy was higher in the right than in the left arcuate fasciculus. These structural asymmetries were linked to functional lateralization, that is, tract volume and fractional anisotropy of the left arcuate fasciculus were positively correlated to the strength of functional language lateralization, as was the volume of the right uncinate fasciculus. In conclusion, the results of the present study suggest that both micro- and macro-structural properties of language-relevant intrahemispheric white matter tracts modulate the behavioral correlates of language lateralization.

Functional Language Lateralization of Semantic Variant PPA (P03.092)

Functional Language Lateralization of Semantic Variant PPA (P03.092)

Sex differences in language asymmetry are age-dependent and small: A large-scale, consonant–vowel dichotic listening study with behavioral and fMRI data

Men are often believed to have a functionally more asymmetrical brain organization than women, but the empirical evidence for sex differences in lateralization is unclear to date. Over the years we have collected data from a vast number of participants using the same consonant–vowel dichotic listening task, a reliable marker for language lateralization. One dataset comprised behavioral data from 1782 participants (885 females, 125 non-right-handers), who were divided in four age groups (children <10 yrs, adolescents = 10–15 yrs, younger adults = 16–49 yrs, and older adults >50 yrs). In addition, we had behavioral and functional imaging (fMRI) data from another 104 younger adults (49 females, aged 18–45 yrs), who completed the same dichotic listening task in a 3T scanner. This database allowed us to comprehensively test whether there is a sex difference in functional language lateralization. Across all participants and in both datasets a right ear advantage (REA) emerged, reflecting left-hemispheric language lateralization. Accordingly, the fMRI data revealed a leftward asymmetry in superior temporal lobe language processing areas. In the N = 1782 dataset no main effect of sex but a significant sex by age interaction emerged: the REA increased with age in both sexes but as a result of an earlier onset in females the REA was stronger in female than male adolescents. In turn, male younger adults showed greater asymmetry than female younger adults (accounting for <1% of variance). There were no sex differences in children and older adults. The males in the fMRI dataset (N = 104) also had a greater REA than females (accounting for 4% of variance), but no sex difference emerged in the neuroimaging data. Handedness did not affect these findings. Taken together, our findings suggest that sex differences in language lateralization as assessed with dichotic listening exist, but they are (a) not necessarily reflected in fMRI data, (b) age-dependent and (c) relatively small.

Presurgical functional transcranial Doppler sonography (fTCD) with intravenous echo enhancing agent SonoVue enables determination of language lateralization in epilepsy patients with poor temporal bone windows

Presurgical determination of language lateralization is important for planning and outcome estimation of neurosurgical interventions in patients with drug-refractory epilepsy. Functional transcranial Doppler sonography (fTCD) provides an established measure for language lateralization using the temporal bone windows for continuous recording of the cerebral blood flow velocity (CBFV) in both middle cerebral arteries (MCAs). However, because of insufficient temporal bone windows, fTCD cannot be applied properly in every patient. Here, we established stable and sufficient CBFV signals in both MCAs using continuous intravenous application of echo-enhancing agent SonoVue in 7 of 10 patients with poor temporal bone windows and were thus able to determine language lateralization. We conclude that the application of SonoVue can solve one principal disadvantage of fTCD and improves the applicability of the technique as a presurgical functional language lateralization procedure.

A combined fMRI and DTI examination of functional language lateralization and arcuate fasciculus structure: Effects of degree versus direction of hand preference

The present study examined the relationship between hand preference degree and direction, functional language lateralization in Broca’s and Wernicke’s areas, and structural measures of the arcuate fasciculus. Results revealed an effect of degree of hand preference on arcuate fasciculus structure, such that consistently-handed individuals, regardless of the direction of hand preference, demonstrated the most asymmetric arcuate fasciculus, with larger left versus right arcuate, as measured by DTI. Functional language lateralization in Wernicke’s area, measured via fMRI, was related to arcuate fasciculus volume in consistent-left-handers only, and only in people who were not right hemisphere lateralized for language; given the small sample size for this finding, future investigation is warranted. Results suggest handedness degree may be an important variable to investigate in the context of neuroanatomical asymmetries.

Structural Correlates of Functional Language Dominance: A Voxel‐Based Morphometry Study

The goal of this study was to explore the structural correlates of functional language dominance by directly comparing the brain morphology of healthy subjects with left- and right-hemisphere language dominance. Twenty participants were selected based on their language dominance from a cohort of subjects with known language lateralization. Structural differences between both groups were assessed by voxel-based morphometry, a technique that automatically identifies differences in the local gray matter volume between groups using high-resolution T1-weighted magnetic resonance images. The main findings can be summarized as follows: (1) Subjects with right-hemisphere language dominance had significantly larger gray matter volume in the right hippocampus than subjects with left-hemisphere language dominance. (2) Leftward structural asymmetries in the posterior superior temporal cortex, including the planum temporale (PT), were observed in both groups. Our study does not support the still prevalent view that asymmetries of the PT are related in a direct way to functional language lateralization. The structural differences found in the hippocampus underline the importance of the medial temporal lobe in the neural language network. They are discussed in the context of recent findings attributing a critical role of the hippocampus in the development of language lateralization.

Hemispheric asymmetry of the arcuate fasciculus

Lateralization of language function is a prominent feature of human brain function, and its underlying structural asymmetry has been recently reported in normal right-handed subjects. By means of diffusion tensor tractography (DTT), we investigated the asymmetry of the language network, namely, the arcuate fasciculus in patients in whom the unilateral language dominance was defined by Wada test. DTT was performed in 24 patients with a focal lesion or an epileptic focus outside the C-shaped segment of the arcuate fasciculus. The arcuate fasciculus was reconstructed by placing two regions-of-interest in the deep white matter lateral to the corona radiata. The pathway was then divided into one terminating in the temporal lobe (FT tract) and the other in the parietal lobe (FP tract). The relative number and volume of the FT and FP tracts in each hemisphere were submitted to repeated measure ANOVA separately, with the hemisphere as a within-subject factor and with the side of pathology as a between subject factor. The FT tract showed a significantly larger number and volume in the language dominant hemisphere than in the non-dominant hemisphere, while, for the FP tract, no significant hemispheric difference was observed in the relative number or volume. There was a tendency that the FT tract was less lateralized when the pathology was located in the dominant hemisphere than in the non-dominant hemisphere. Dominance of the FT tract in the language dominant hemisphere was demonstrated for the first time in a patient population and implicated a clinical utility of DTT for non-invasive evaluation of language lateralization. Our preliminary study might indicate reorganization of the language network in conjunction with pathology.