Right Hemisphere Language Dominance Research Articles

H - 24 The Role of Bilingual Neuropsychologists in Presurgical Epilepsy Evaluations: La Evaluación Comprensiva en Español.

As neuropsychologists continually work to establish clinical standards of practice for evaluation of linguistically and culturally diverse children with epilepsy (Berrios-Siervo et al., 2023), this case study supports efforts to document complex assessment procedures with an adolescent who recently immigrated from Mexico to the U.S. A 16-year-old, right-handed, primarily Spanish-speaking, Hispanic male with intractable epilepsy (complex partial seizures) was referred for a presurgical neuropsychological evaluation. Medication was initiated in Mexico at age 11years, but increased frequency and severity of seizures prompted immigration to the U.S. at age 14 for further treatment. EEG and brain MRI indicated left hemisphere involvement. Magnetoencephalography results indicated right-hemisphere dominance for receptive language. Functional MRI (fMRI) indicated left-hemisphere dominance. Subsequent Wada and bilateral language mapping results supported left-hemisphere dominance. Personal history was significant for anxiety and depressed mood. Bilingual neuropsychologists completed a presurgical evaluation, fMRI, stereo EEG language mapping, and Wada in Spanish. He was seizure-free 6months post selective left temporal resection. He recently completed his1-year post-op evaluation. Baseline testing indicated average neurocognitive functioning, with select relative weaknesses lacking strong evidence for lateralization/localization. Post-operative consultation/ evaluation at 6 and 12months, respectively, revealed the patient was doing well academically with perceived improvements in attention and memory and minimal language difficulties. Reported improvements in mood were attributed to family reunification and increased social engagement. In addition to pre/post-surgical assessment in Spanish, bilingual neuropsychologists are uniquely positioned to contribute to the establishment of culturally-informed, standardized approaches to essential aspects of the presurgical workup (e.g., language mapping, Wada).

Developmental Dynamic Dysphasia: Are Bilateral Brain Abnormalities a Signature of Inefficient Neural Plasticity?

The acquisition and evolution of speech production, discourse and communication can be negatively impacted by brain malformations. We describe, for the first time, a case of developmental dynamic dysphasia (DDD) in a right-handed adolescent boy (subject D) with cortical malformations involving language-eloquent regions (inferior frontal gyrus) in both the left and the right hemispheres. Language evaluation revealed a markedly reduced verbal output affecting phonemic and semantic fluency, phrase and sentence generation and verbal communication in everyday life. Auditory comprehension, repetition, naming, reading and spelling were relatively preserved, but executive function was impaired. Multimodal neuroimaging showed a malformed cerebral cortex with atypical configuration and placement of white matter tracts bilaterally and abnormal callosal fibers. Dichotic listening showed right hemisphere dominance for language, and functional magnetic resonance imaging (fMRI) additionally revealed dissociated hemispheric language representation with right frontal activation for phonology and bilateral dominance for semantic processing. Moreover, subject D also had congenital mirror movements (CMM), defined as involuntary movements of one side of the body that mirror intentional movements of the other side. Transcranial magnetic stimulation and fMRI during voluntary unimanual (left and right) hand movements showed bilateral motor cortex recruitment and tractography revealed a lack of decussation of bilateral corticospinal tracts. Genetic testing aimed to detect mutations that disrupt the development of commissural tracts correlating with CMM (e.g., Germline DCC mutations) was negative. Overall, our findings suggest that DDD in subject D resulted from the underdevelopment of the left inferior frontal gyrus with limited capacity for plastic reorganization by its homologous counterpart in the right hemisphere. Corpus callosum anomalies probably contributed to hinder interhemispheric connectivity necessary to compensate language and communication deficits after left frontal involvement.

Schizotypy and altered hemispheric asymmetries: The role of cilia genes

Schizophrenia patients have a higher probability of altered structural and functional differences between the left and right hemisphere. Schizotypy as its nonclinical manifestation has been related to a higher incidence of non-right-handedness and atypical right-hemispheric language dominance. It has been suggested that genes involved in cilia function might link brain asymmetry and neurodevelopmental disorders. We assessed DNA methylation in the promoter regions of seven candidate genes involved in cilia function and psychiatric disorders from buccal cells and investigated their association with schizotypy and language lateralization in 60 healthy adults. Moreover, we determined microstructural properties of the planum temporale in a subsample of 52 subjects using neurite orientation dispersion and density imaging (NODDI). We found a significant association between schizotypy and DNA methylation in the AHI1 promoter region. Moreover, AHI1 DNA methylation significantly predicted language lateralization and asymmetry in estimated planum temporale neurite density. Finally, stronger leftward asymmetry in estimated neurite density was associated with a more pronounced right ear advantage (left hemisphere dominance) in the forced-right condition of the dichotic listening task, measuring attentional modulation of language lateralization. Our results are in line with a shared molecular basis of schizotypy and functional hemispheric asymmetries that is based on cilia function.

Three- and four-dimensional mapping of speech and language in patients with epilepsy.

We have provided 3-D and 4D mapping of speech and language function based upon the results of direct cortical stimulation and event-related modulation of electrocorticography signals. Patients estimated to have right-hemispheric language dominance were excluded. Thus, 100 patients who underwent two-stage epilepsy surgery with chronic electrocorticography recording were studied. An older group consisted of 84 patients at least 10 years of age (7367 artefact-free non-epileptic electrodes), whereas a younger group included 16 children younger than age 10 (1438 electrodes). The probability of symptoms transiently induced by electrical stimulation was delineated on a 3D average surface image. The electrocorticography amplitude changes of high-gamma (70-110 Hz) and beta (15-30 Hz) activities during an auditory-naming task were animated on the average surface image in a 4D manner. Thereby, high-gamma augmentation and beta attenuation were treated as summary measures of cortical activation. Stimulation data indicated the causal relationship between (i) superior-temporal gyrus of either hemisphere and auditory hallucination; (ii) left superior-/middle-temporal gyri and receptive aphasia; (iii) widespread temporal/frontal lobe regions of the left hemisphere and expressive aphasia; and (iv) bilateral precentral/left posterior superior-frontal regions and speech arrest. On electrocorticography analysis, high-gamma augmentation involved the bilateral superior-temporal and precentral gyri immediately following question onset; at the same time, high-gamma activity was attenuated in the left orbitofrontal gyrus. High-gamma activity was augmented in the left temporal/frontal lobe regions, as well as left inferior-parietal and cingulate regions, maximally around question offset, with high-gamma augmentation in the left pars orbitalis inferior-frontal, middle-frontal, and inferior-parietal regions preceded by high-gamma attenuation in the contralateral homotopic regions. Immediately before verbal response, high-gamma augmentation involved the posterior superior-frontal and pre/postcentral regions, bilaterally. Beta-attenuation was spatially and temporally correlated with high-gamma augmentation in general but with exceptions. The younger and older groups shared similar spatial-temporal profiles of high-gamma and beta modulation; except, the younger group failed to show left-dominant activation in the rostral middle-frontal and pars orbitalis inferior-frontal regions around stimulus offset. The human brain may rapidly and alternately activate and deactivate cortical areas advantageous or obtrusive to function directed toward speech and language at a given moment. Increased left-dominant activation in the anterior frontal structures in the older age group may reflect developmental consolidation of the language system. The results of our functional mapping may be useful in predicting, across not only space but also time and patient age, sites specific to language function for presurgical evaluation of focal epilepsy.

Right hemisphere dominance for language in a woman with schizophrenia and a porencephalic cyst of the left hemisphere

ABSTRACTA large left hemisphere porencephalic cyst was incidentally found in a 48-year-old woman (MS) with a Diagnostic and Statistical Manual (DSM)-5 diagnosis of schizophrenia. The encephaloclastic characteristics of the cyst indicated that it was acquired between the 22nd and 24th gestational weeks, after the major waves of neuronal migration had tapered off. The cyst destroyed the left temporal and occipital lobes, and the inferior parietal lobule. Surprisingly, MS had no evidence of aphasia, alexia, agraphia, or ideational apraxia; in contrast, cognitive functions dependent on the integrity of the right hemisphere were severely impaired. To test the hypothesis that the development of language in MS took place at the expense of functions that are normally carried out by the right hemisphere, we investigated MS’s correlates of oral comprehension with fMRI as a proxy for auditory comprehension and other cognitive functions strongly lateralized to the posterior left hemisphere, such as ideational praxis and reading. Comprehension of spoken language engaged the homologous of Wernicke’s area in the right planum temporale. Porencephaly may represent a natural model of neuroplasticity supervening at predictable epochs of prenatal development.

Impaired reading not due to visual field loss in a patient with a right-hemipsheric lesion

We describe a right-handed patient (M.B.), who developed left hemianopsia and a severe reading impairment after right occipital–parietal hemorrhage. The pattern of his reading deficit was very similar to that of pure alexia (alexia-without-agraphia): extremely slow reading times with frequent grapheme substitutions and omissions. A test of letter reading while controlling for saccadic eye movements and hemifield of presentation ruled out hemianoptic alexia. Although there have already been reports of reading impairments in right handers following right- hemispheric lesions, ours is, to the best of our knowledge, the first where visual field loss can be definitely excluded as the main cause. Based on a standard neuropsychological assessment and on additional behavioral tests, we argue that M.B.’s difficulties are unlikely to be due to right-hemisphere dominance for language. After considering several candidate explanations, we suggest that M.B.’s symptoms may be related to an impairment in attentional processes related to reading.

White-matter microstructure and language lateralization in left-handers: A whole-brain MRI analysis

Most people are left-hemisphere dominant for language. However the neuroanatomy of language lateralization is not fully understood. By combining functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), we studied whether language lateralization is associated with cerebral white-matter (WM) microstructure. Sixteen healthy, left-handed women aged 20–25 were included in the study. Left-handers were targeted in order to increase the chances of involving subjects with atypical language lateralization. Language lateralization was determined by fMRI using a verbal fluency paradigm. Tract-based spatial statistics analysis of DTI data was applied to test for WM microstructural correlates of language lateralization across the whole brain. Fractional anisotropy and mean diffusivity were used as indicators of WM microstructural organization. Right-hemispheric language dominance was associated with reduced microstructural integrity of the left superior longitudinal fasciculus and left-sided parietal lobe WM. In left-handed women, reduced integrity of the left-sided language related tracts may be closely linked to the development of right hemispheric language dominance. Our results may offer new insights into language lateralization and structure–function relationships in human language system.

Complementary hemispheric specialization for language production and visuospatial attention

Language production and spatial attention are the most salient lateralized cerebral functions, and their complementary specialization has been observed in the majority of the population. To investigate whether the complementary specialization has a causal origin (the lateralization of one function causes the opposite lateralization of the other) or rather is a statistical phenomenon (different functions lateralize independently), we determined the lateralization for spatial attention in a group of individuals with known atypical right hemispheric (RH) lateralization for speech production, based on a previous large-scale screening of left-handers. We show that all 13 participants with RH language dominance have left-hemispheric dominance for spatial attention, and all but one of 16 participants with left-hemispheric language dominance are RH dominant for spatial attention. Activity was observed in the dorsal fronto-parietal pathway of attention, including the inferior parietal sulcus and superior parietal lobule, the frontal eye-movement field, and the inferior frontal sulcus/gyrus, and these regions functionally colateralized in the hemisphere dominant for attention, independently of the side of lateralization. Our results clearly support the Causal hypothesis about the complementary specialization, and we speculate that it derives from a longstanding evolutionary origin. We also suggest that the conclusions about lateralization based on an unselected sample of the population and laterality assessment using coarse functional transcranial Doppler sonography should be interpreted with more caution.

Crossed Aphasia in a Dextral Patient With Logopenic/Phonological Variant of Primary Progressive Aphasia

Crossed aphasia is a rare phenomenon, with a prevalence of 1% to 2% among all right-handed patients. Two crossed aphasic patients with a nonfluent variant of primary progressive aphasia (PPA) have been reported previously. This report aims to document for the first time the occurrence of crossed logopenic progressive aphasia in a dextral patient. A 57-year-old monolingual housewife presented with word-finding difficulties. She was strongly right handed, had no clinical history for brain damage to the left hemisphere, and no left handers in her family history. Her language comprised simple, grammatically correct sentences with a fluctuating speech rate and intermittent word-finding pauses. Rare phonological errors were noted. Sentence repetition tasks showed impairments with grammatically complex sentences. Comprehension was intact as were writing and reading. The language disability remained isolated for 3 years. Cranial magnetic resonance imaging depicted somewhat asymmetrical atrophy of the parietal lobes (R>L), whereas single-photon-emitted computed tomographic imaging demonstrated hypoperfusion in the right parietal cortex, indicating right hemisphere dominance for language. This case report provides evidence that crossed PPA can present with a logopenic variant in addition to the nonfluent type demonstrated by others. Functional neuroimaging showed unexpected right-sided hypoperfusion in this case with only subtle structural brain asymmetry, implicating a reverse pattern of language dominance.

Dichotic listening in children: Age-related changes in direction and magnitude of ear advantage

Children between the ages of 5 and 12 years were tested with dichotic listening tests utilizing single syllable words and random presentations of digits. They produced a higher prevalence of left ear dominance than expected, especially among right-handed children when tested with words. Whether more children demonstrate the LEA because of right hemisphere dominance for language or because there is less stability in ear advantage direction at younger ages cannot be fully resolved by this study. When ear advantages were measured by subtracting each child’s lower score from the higher score without regard to right or left direction, an age-related trend toward lower measures of ear advantage was evident. This trend was greater for dichotic words than for dichotic digits. Structural factors that may be related to these results and possible influences of attention and verbal workload on the two kinds of dichotic stimuli are discussed.

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.

Neuroimaging study on brain asymmetries in situs inversus totalis

Situs inversus totalis (SI) is a rare condition in which all visceral organs are arranged as mirror images of the usual pattern. The objective of this study was to determine whether SI individuals have reversed brain asymmetries. We performed a neuroimaging study on 3 SI subjects and 11 control individuals with normally arranged visceral organs. The language-dominant hemisphere was determined by magnetoencephalography. Left-hemispheric dominance was observed in 1 SI subject and all controls, whereas right-hemispheric dominance was observed in the remaining 2 SI subjects. Statistical analysis revealed that language dominance patterns in SI subjects were different from those in the controls, suggesting that the developmental mechanisms underlying visceral organ asymmetries are related to those underlying functional brain asymmetry. Anatomical brain asymmetries were determined by magnetic resonance imaging. SI subjects had the same planum temporale (PT) asymmetry pattern as the controls, but a reversed petalia asymmetry pattern. The inferior frontal gyrus (IFG) asymmetry pattern varied within both groups, indicating a relationship between the rightward IFG and right-hemispheric language dominance. These results suggest that the developmental mechanisms underlying visceral organ asymmetries are related to those underlying petalia asymmetry but not to those underlying PT and IFG asymmetries, and that brain asymmetries might develop via multiple region-dependent mechanisms.

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

The aim of the study was to evaluate the sensitivity and reliability of assessing hemispheric language dominance with functional magnetic resonance imaging (fMRI) using a 'free reversed association task.' Thirty-nine healthy subjects (13 dextrals, 13 sinistrals and 13 bimanuals) underwent two repeated fMRI sessions. In the active phases sets of words were presented via headphones, and an associated target item was named. During the baseline phases a standard answer was given after listening to unintelligible stimuli. Data were preprocessed with SPM, and then laterality indices (LI) and reliability coefficients (RC) were calculated. Extensive frontal, temporal and parietal activations were found. Seventy-eight percent of the subjects showed left-hemispheric dominance, 5% showed right-hemispheric dominance, and 17% had bilateral language representations. The incidence of right-hemispheric language dominance was 4.3 times higher in a left-hander with a handedness quotient (HQ) of -90 than in a right-hander with a HQ of +90. The RC was 0.61 for combined ROIs (global network). Strong correlations were found between the two session LIs (r = 0.95 for the global network). 'Free reversed association' is a sensitive and reliable task for the determination of individual language lateralization. This suggests that the task may be used in a clinical setting.

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

To determine the role of functional magnetic resonance (MR) imaging in assessing hemispheric language dominance in epilepsy and nonepilepsy populations. A Bayesian analysis study was performed. The study was based on data from the published literature; thus, institutional review board approval was not required. The literature was reviewed to obtain pretest probabilities and likelihood ratios, which were analyzed to determine the posttest probability of language dominance by using functional MR imaging. Pretest probabilities of different hand dominances in epilepsy and nonepilepsy populations were obtained from the largest studies available in the literature. Likelihood ratios were derived from the sensitivity and specificity of functional MR imaging by using electrocortical stimulation (ECS) and the Wada test as reference standards. Likelihood ratios for functional MR in determining language dominance were 9.3 and 12.3 with ECS and the Wada test as reference standards, respectively. Use of functional MR increased the final posttest probabilities of hemispheric language dominance in epilepsy and nonepilepsy populations. In the nonepilepsy population, regardless of hand dominance, there was very high posttest probability (>or=96%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the epilepsy population with right-hand dominance or ambidexterity, there was very high posttest probability (>or=95%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the left-handed nonepileptic subjects, there was high posttest probability (81%-83%) of a correlation between functional MR hemisphere activation and definite right-hemisphere language dominance. In the left-handed epilepsy population, there was high posttest probability (80%-97%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the epilepsy population with ambidexterity, there was high posttest probability (80%-87%) of correlations between functional MR hemisphere activation and both definite right-hemisphere and bilateral language dominance. Use of functional MR increases importantly the posttest probabilities of hemispheric language dominance in multiple subgroups of individuals with and without epilepsy.

Cerebellar activation in right-hemispheric language dominance following early left-sided brain lesions

Cerebellar activation in right-hemispheric language dominance following early left-sided brain lesions

Primary progressive aphasia: Reversed asymmetry of atrophy and right hemisphere language dominance

Primary progressive aphasia (PPA) is almost always associated with asymmetrical left hemisphere degeneration. The authors report that right hemisphere atrophy in a patient with PPA was associated with atypical right hemisphere dominance for language. This suggests that neuronal damage in PPA is therefore tightly linked to the underlying anatomy of the language network.

Crossed cerebro-cerebellar language dominance.

In addition to its traditional role in motor control, the cerebellum has been implicated in various cognitive and linguistic functions. Lesion, anatomic, and functional imaging studies indicate a link between left frontal language regions and the right cerebellum. To probe the specificity of this circuit, we examined the association between language-related lateralized activation of the frontal cortex with lateralized activation of the cerebellum. Functional magnetic resonance imaging (fMRI) was carried out during letter-cued word generation in 14 healthy subjects: 7 subjects displayed typical left-hemisphere and 7 subjects displayed atypical right-hemisphere language dominance. We found activation of the cerebellar hemisphere contralateral to the language-dominant cerebral hemisphere in each subject. The cerebellar activation was confined to the lateral posterior cerebellar hemisphere (lobule VI, VII B, Cr I, Cr II). This study demonstrates that crossed cerebral and cerebellar language dominance is a typical characteristic of brain organization. The functional significance of the reported activations can now be tested in patients with lesions of the lateral posterior cerebellum.

RESPONSE

To the Editor: We thank Dr. Derakhshan for his interesting general remarks on hemispheric dominance. It is an exciting speculation whether the patient described in our article 1 might be a “fake-hander.” However, the distinction between neural and behavioral handedness seems quite theoretical and not appropriate in the evaluation of patients before surgical intervention. It has been known for a long time that the strong coincidence between right-handedness and left hemisphere language dominance in normal subjects is much less consistent in patients with epilepsy 2. Neither neural nor behavioral handedness is suitable to predict the cerebral language organization in patients with epilepsy. Therefore it is the aim of the procedures applied in the presurgical evaluation [Wada test, functional magnetic resonance imaging (fMRI), cortical stimulation] not to analyze the laterality of movement control (handedness and speech), but to determine whether a surgical resection in a given patient is likely to induce a deficit (e.g., language, motor, memory). For this purpose we—and as far as we know, all major epilepsy centers—indeed do rely on the Wada test. In accordance with Loring et al. 3, we believe that the Wada test is the least ambiguous method to test for hemispheric language dominance. Our reliance is not restrained by the articles cited by Dr. Derakhshan. The variability of the results of the studies by Risse et al. 4 and by Mamelak et al. 5 simply reflects differences between the examined patient populations. The results of Risse et al. 4 represent the generally accepted proportion of the different types of cerebral language representation in a large sample of epilepsy patients (82% left dominant, 18% atypical). On the contrary, the observations by Mamelak et al. 5 resulted from a patient group with severe bilateral epilepsies in whom a callosotomy was performed. It is not surprising at all that atypical (i.e., non–left-dominant language representation) is highly overrepresented in this selected group. From our point of view, it is not dubious to speculate about the reasons for the right-hemisphere language dominance in our patient. Strong evidence from the literature indicates that atypical language dominance and non–right-handedness is frequently observed in patients with early left hemisphere brain lesions or early onset of seizures originating from the left hemisphere 1, 3, 5. Therefore it remains open whether the right-hemisphere language dominance in our patient was primary or a consequence of his left-hemisphere injury, representing functional plasticity. The Wada test and cortical stimulation cannot be completely replaced in the presurgical evaluation of patients with epilepsy. In our opinion, determination of the “neural handedness” is completely useless in this context. fMRI will help to reduce the number of patients in whom invasive procedures are mandatory 6.

How atypical is atypical language dominance?

Atypical, right-hemisphere language dominance is poorly understood. It is often observed in patients with brain reorganization due to lesions early in life. It can also be encountered in seemingly normal individuals. We compared the patterns of neural language activation in 7 individuals with left- and 7 with right-hemisphere language dominance, none of whom had any evidence of brain lesions. We speculated that incongruencies in the activation patterns in atypical, right-hemisphere language dominance could indicate a reorganized neural language system after undetected early brain damage. Functional magnetic resonance imaging analysis of brain activation during phonetic word generation demonstrated (1) no increased activation in the subdominant hemisphere in right compared to left language dominance, (2) a similar variability in the pattern of activation in both groups, and (3) a mirror reverse pattern of activation in right- compared to left-hemisphere dominant subjects. These findings support the view that in individuals with an unrevealing medical history right-hemispheric dominance constitutes a natural rather than an abortive variant of language lateralization.

Spanish Language Mapping Using MEG: A Validation Study

The purpose of the present study was to compare magnetoencephalography (MEG) data with the results of the intracarotid amytal procedure (IAP). Twenty-one native Spanish-speaking patients with intractable epilepsy underwent MEG language mapping. A subset of 8 patients also underwent an IAP. With the exception of 2 patients who showed right hemisphere dominance, all other patients showed left hemisphere dominance for language on the MEG recording. The IAP findings were consistent with MEG results in 7 patients. The eighth patient who, according to the MEG data, had probable right hemisphere dominance for language did not show clear hemispheric specialization for language on the IAP and suffered a transient global aphasia following a right temporal lobotomy. These results suggests that MEG-based language mapping can play an important role in presurgical clinical evaluation.