Left Hemisphere Language Dominance Research Articles

Impairment only on the fluency subtest of the Frontal Assessment Battery after prefrontal lesions

The Frontal Assessment Battery is a set of six subtests that is used widely to assess frontal cortical executive dysfunction. Performance on the Frontal Assessment Battery has been shown to be sensitive to various neurodegenerative diseases, but it has never been shown to be sensitive to damage restricted to the frontal cortex. Thus, despite its wide use, it has never been validated on an appropriate population of patients with frontal lesions. The present study shows that, of the six subtests that comprise the Frontal Assessment Battery, only performance on the verbal fluency subtest (mental flexibility) was specifically sensitive to injury restricted to the frontal cortex. Performance of patients with damage to the dorsal part of the medial frontal region in the language-dominant left hemisphere was impaired. None of these patients was aphasic at the time of testing. The critical region in the dorsomedial frontal cortex includes the supplementary speech zone but is not restricted to it: it extends into the cingulate motor region and the paracingulate cortex as well as the medial prefrontal areas 8 and 9. The results indicate that the Frontal Assessment Battery is not a sensitive measure of prefrontal cortical dysfunction, except for the verbal fluency subtest.

P 45. The right planum temporale is involved in auditory attention-evidence from TMS

It is well known that the planum temporale (PT) carries out spectro-temporal analysis of auditory stimuli, which is crucial for speech, for example. There are suggestions, however, that the PT is also involved in auditory attention, specifically in the discrimination and selection of left and right ear stimuli. We aimed to provide a direct test for the role of the PT in auditory attention. Fourteen participants (7 men, 7 women) completed the Bergen Dichotic Listening Test. In this test two different consonant–vowel syllables (e.g., “ba” and “da”) are presented simultaneously, one to each ear, and participants are asked to report the sound they heard best or most clearly. Each participant completed the test three times, that is, after repetitive transcranial magnetic stimulation (rTMS) for 10 min at a frequency of 1 Hz had been applied to the left and the right PT (located with anatomical brain scans), and after sham stimulation with a placebo coil (control). The order of left, right and sham PT stimulation was counterbalanced. After sham stimulation the typical right ear advantage emerged, that is, participants reported relatively more right than left ear stimuli reflecting a left-hemispheric dominance for language. However, rTMS over the right but not left PT significantly reduced the right ear advantage. This was the result of participants reporting more left and fewer right ear stimuli after right PT stimulation, suggesting there was a leftward shift in stimulus selection. Our findings support the notion that the PT, and the right PT in particular, is involved in stimulus selection and auditory attention, although its primary function is auditory perception.

P 114. Anodal transcranial direct current stimulation in early treatment of post-stroke non-fluent aphasia

Introduction Neuroimaging studies suggests that increased level of cortical excitability in the stroke-affected left hemisphere is associated with better language improvement in aphasic patients. Recent neurostimulating studies showed that combination of behavioural therapy with excitatory anodal transcranial direct current stimulation (A-tDCS) of perilesional cortex in the language-dominant left hemisphere improve language performance in patients with chronic post-stroke aphasia. Objective The aim of this study was to investigate the impact of A-tDCS on language in aphasics in the early post-stroke rehabilitation period when most adaptive changes in cortical excitability are possible and most conventional therapies are conducted. We hypothesized that early reactivation of preserved language-related structures and their neighboring regions may facilitate the restoration of the neuronal language network manifested by better naming. Methods 24 patients with moderate or severe non-fluent aphasia were randomized to receive 15 consecutive daily sessions of A-tDCS (1 mA, 10 min; A-tDCS group = 14) or sham tDCS (1 mA, 25 s; sham tDCS group = 10) over Broca’s area followed by 45-min routine speech and language training. Naming ability was assessed before and after the rehabilitation, and three months later using Boston Naming Test. Naming accuracy and speed were chosen as outcome measures. Results Although both groups significantly improved after the therapy, there were no statistically significant differences between groups in either short-term or long-term tDCS effects when naming accuracy and naming time were analyzed. However, for response time A-tDCS group obtained higher effect sizes both post-treatment and at the 3-month follow-up. Conclusions The findings provide only a weak evidence of A-tDCS behavioural gains during early neurorehabilitation of post-stroke aphasia. Further research is needed to investigate the effectiveness of this kind of neuromodulation. Different modes and parameters of tDCS should be explored considering such important factors determining recovery from aphasia as type and severity of language impairment, lesion site and size, time since stroke, and degree of hemispheric language laterality.

FOXP2 variation modulates functional hemispheric asymmetries for speech perception

Left-hemispheric language dominance is a well-known characteristic of the human language system, but the molecular mechanisms underlying this crucial feature of vocal communication are still far from being understood. The forkhead box P2 gene FOXP2, which has been related to speech development, constitutes an interesting candidate gene in this regard. Therefore, the present study was aimed at investigating effects of variation in FOXP2 on individual language dominance. To this end, we used a dichotic listening and a visual half-field task in a sample of 456 healthy adults. The FOXP2 SNPs rs2396753 and rs12533005 were found to be significantly associated with the distribution of correct answers on the dichotic listening task. These results show that variation in FOXP2 may contribute to the inter-individual variability in hemispheric asymmetries for speech perception.

The Right Planum Temporale Is Involved in Stimulus-Driven, Auditory Attention – Evidence from Transcranial Magnetic Stimulation

It is well known that the planum temporale (PT) area in the posterior temporal lobe carries out spectro-temporal analysis of auditory stimuli, which is crucial for speech, for example. There are suggestions that the PT is also involved in auditory attention, specifically in the discrimination and selection of stimuli from the left and right ear. However, direct evidence is missing so far. To examine the role of the PT in auditory attention we asked fourteen participants to complete the Bergen Dichotic Listening Test. In this test two different consonant-vowel syllables (e.g., “ba” and “da”) are presented simultaneously, one to each ear, and participants are asked to verbally report the syllable they heard best or most clearly. Thus attentional selection of a syllable is stimulus-driven. Each participant completed the test three times: after their left and right PT (located with anatomical brain scans) had been stimulated with repetitive transcranial magnetic stimulation (rTMS), which transiently interferes with normal brain functioning in the stimulated sites, and after sham stimulation, where participants were led to believe they had been stimulated but no rTMS was applied (control). After sham stimulation the typical right ear advantage emerged, that is, participants reported relatively more right than left ear syllables, reflecting a left-hemispheric dominance for language. rTMS over the right but not left PT significantly reduced the right ear advantage. This was the result of participants reporting more left and fewer right ear syllables after right PT stimulation, suggesting there was a leftward shift in stimulus selection. Taken together, our findings point to a new function of the PT in addition to auditory perception: particularly the right PT is involved in stimulus selection and (stimulus-driven), auditory attention.

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.

Response inhibition is modulated by functional cerebral asymmetries for facial expression perception

The efficacy of executive functions is critically modulated by information processing in earlier cognitive stages. For example, initial processing of verbal stimuli in the language-dominant left-hemisphere leads to more efficient response inhibition than initial processing of verbal stimuli in the non-dominant right hemisphere. However, it is unclear whether this organizational principle is specific for the language system, or a general principle that also applies to other types of lateralized cognition. To answer this question, we investigated the neurophysiological correlates of early attentional processes, facial expression perception and response inhibition during tachistoscopic presentation of facial “Go” and “Nogo” stimuli in the left and the right visual field (RVF). Participants committed fewer false alarms after Nogo-stimulus presentation in the left compared to the RVF. This right-hemispheric asymmetry on the behavioral level was also reflected in the neurophysiological correlates of face perception, specifically in a right-sided asymmetry in the N170 amplitude. Moreover, the right-hemispheric dominance for facial expression processing also affected event-related potentials typically related to response inhibition, namely the Nogo-N2 and Nogo-P3. These findings show that an effect of hemispheric asymmetries in early information processing on the efficacy of higher cognitive functions is not limited to left-hemispheric language functions, but can be generalized to predominantly right-hemispheric functions.

Caffeine improves left hemisphere processing of positive words.

A positivity advantage is known in emotional word recognition in that positive words are consistently processed faster and with fewer errors compared to emotionally neutral words. A similar advantage is not evident for negative words. Results of divided visual field studies, where stimuli are presented in either the left or right visual field and are initially processed by the contra-lateral brain hemisphere, point to a specificity of the language-dominant left hemisphere. The present study examined this effect by showing that the intake of caffeine further enhanced the recognition performance of positive, but not negative or neutral stimuli compared to a placebo control group. Because this effect was only present in the right visual field/left hemisphere condition, and based on the close link between caffeine intake and dopaminergic transmission, this result points to a dopaminergic explanation of the positivity advantage in emotional word recognition.

Dynamic network structure of interhemispheric coordination

Fifty years ago Gazzaniga and coworkers published a seminal article that discussed the separate roles of the cerebral hemispheres in humans. Today, the study of interhemispheric communication is facilitated by a battery of novel data analysis techniques drawn from across disciplinary boundaries, including dynamic systems theory and network theory. These techniques enable the characterization of dynamic changes in the brain’s functional connectivity, thereby providing an unprecedented means of decoding interhemispheric communication. Here, we illustrate the use of these techniques to examine interhemispheric coordination in healthy human participants performing a split visual field experiment in which they process lexical stimuli. We find that interhemispheric coordination is greater when lexical information is introduced to the right hemisphere and must subsequently be transferred to the left hemisphere for language processing than when it is directly introduced to the language-dominant (left) hemisphere. Further, we find that putative functional modules defined by coherent interhemispheric coordination come online in a transient manner, highlighting the underlying dynamic nature of brain communication. Our work illustrates that recently developed dynamic, network-based analysis techniques can provide novel and previously unapproachable insights into the role of interhemispheric coordination in cognition.

The neuronal infrastructure of speaking

Models of speaking distinguish producing meaning, words and syntax as three different linguistic components of speaking. Nevertheless, little is known about the brain’s integrated neuronal infrastructure for speech production. We investigated semantic, lexical and syntactic aspects of speaking using fMRI. In a picture description task, we manipulated repetition of sentence meaning, words, and syntax separately. By investigating brain areas showing response adaptation to repetition of each of these sentence properties, we disentangle the neuronal infrastructure for these processes. We demonstrate that semantic, lexical and syntactic processes are carried out in partly overlapping and partly distinct brain networks and show that the classic left-hemispheric dominance for language is present for syntax but not semantics.

Multimodality language mapping in patients with left-hemispheric language dominance on Wada test

ObjectiveWe determined the utility of electrocorticography (ECoG) and stimulation for detecting language-related sites in patients with left-hemispheric language-dominance on Wada test. MethodsWe studied 13 epileptic patients who underwent language mapping using event-related gamma-oscillations on ECoG and stimulation via subdural electrodes. Sites showing significant gamma-augmentation during an auditory-naming task were defined as language-related ECoG sites. Sites at which stimulation resulted in auditory perceptual changes, failure to verbalize a correct answer, or sensorimotor symptoms involving the mouth were defined as language-related stimulation sites. We determined how frequently these methods revealed language-related sites in the superior-temporal, inferior-frontal, dorsolateral-premotor, and inferior-Rolandic regions. ResultsLanguage-related sites in the superior-temporal and inferior-frontal gyri were detected by ECoG more frequently than stimulation (p<0.05), while those in the dorsolateral-premotor and inferior-Rolandic regions were detected by both methods equally. Stimulation of language-related ECoG sites, compared to the others, more frequently elicited language symptoms (p<0.00001). One patient developed dysphasia requiring in-patient speech therapy following resection of the dorsolateral-premotor and inferior-Rolandic regions containing language-related ECoG sites not otherwise detected by stimulation. ConclusionsLanguage-related gamma-oscillations may serve as an alternative biomarker of underlying language function in patients with left-hemispheric language-dominance. SignificanceMeasurement of language-related gamma-oscillations is warranted in presurgical evaluation of epileptic patients.

Test de escucha dicótica para niños hispanohablantes: validación de unas nuevas series de pares de palabras y de sílabas en castellano

Dichotic listening test can estimate hemispheric dominance for language. To study the usefulness of a new set of dichotic pairs of Spanish stimuli in middle childhood. The stratified control group comprised 40 healthy, right-handed children, aged 3.5- 7.5 years, of both sexes, with average ability at speaking Spanish. The clinical sample comprised 12 children with right spastic hemi-paretic cerebral palsy, average general intelligence and sentence repetition index over -2z. Each listening series is composed of 20 age-appropriate dichotic pairs: one syllable, word, or number; or trains of two or three syllables or numbers. Voice onset time, duration and stress of stimuli were balanced. Hemispheric dominance index (HDI) for language was calculated using a formula with the scores of stimuli from right or left ears. Statistical analysis evaluated the age-related accuracy and discriminant power of each HDI. In the non-forced attention paradigm, the range of HDI is 0-200. Values of HDI ≥ 112 indicate left hemisphere dominance for language, whereas values of HDI ≤ 88 indicate right hemisphere dominance. All 40 typical subjects showed left HDI for language, without influence of age and sex. In contrast, ten out of twelve (83%) right hemiparetic children had right HDI. The results show that this new set of dichotic pairs is useful in the initial assessment of cerebral dominance for language and valid for use in Spanish speaking children aged 3.5 years or more.

Foreign accent syndrome caused by a left temporal-parietal ischaemic stroke.

Karanasios P, Loukopoulou P, Zampakis P, Tiligadas T, Makridou A, Doukas V, Argyriou AA. Foreign accent syndrome caused by a left temporal-parietal ischaemic stroke. We present the first reported case of a Greek patient with foreign accent syndrome (FAS) secondary to a left temporal-parietal ischemic stroke. A 76 year-old right-handed, Greek in origin, male was referred because he had suddenly manifested changes in speech expression. The neurological examination revealed that his prior typical English-Australian accent resembled a mixture of Greek and English-Britain accent consistent with FAS, though he had visited only once Greece the last 15 years and never had been to United Kingdom. A brain Magnetic Resonance Imaging scan depicted an ischemic temporal lesion in the language-dominant left hemisphere, affecting the left posterior superior and middle temporal gyri, as well as the ipsilateral inferior supramarginal angular gyrus and posterior insula. We might suggest that FAS in our patient was induced because of interrupted cortical-subcortical feedback pathways. The phenomenon of subcortical-cortical diaschisis might also have contributed to its clinical manifestation.

Optimizing estimation of hemispheric dominance for language using magnetic source imaging

The efficacy of magnetoencephalography (MEG) as an alternative to invasive methods for investigating the cortical representation of language has been explored in several studies. Recently, studies comparing MEG to the gold standard Wada procedure have found inconsistent and often less-than accurate estimates of laterality across various MEG studies. Here we attempted to address this issue among normal right-handed adults ( N = 12) by supplementing a well-established MEG protocol involving word recognition and the single dipole method with a sentence comprehension task and a beamformer approach localizing neural oscillations. Beamformer analysis of word recognition and sentence comprehension tasks revealed a desynchronization in the 10–18 Hz range, localized to the temporo-parietal cortices. Inspection of individual profiles of localized desynchronization (10–18 Hz) revealed left hemispheric dominance in 91.7% and 83.3% of individuals during the word recognition and sentence comprehension tasks, respectively. In contrast, single dipole analysis yielded lower estimates, such that activity in temporal language regions was left-lateralized in 66.7% and 58.3% of individuals during word recognition and sentence comprehension, respectively. The results obtained from the word recognition task and localization of oscillatory activity using a beamformer appear to be in line with general estimates of left hemispheric dominance for language in normal right-handed individuals. Furthermore, the current findings support the growing notion that changes in neural oscillations underlie critical components of linguistic processing.

Variation in the NMDA receptor 2B subunit gene GRIN2B is associated with differential language lateralization

Variations in the N-methyl- d-aspartate receptor 2B subunit gene ( GRIN2B) have been associated with schizophrenia, a psychiatric disorder associated with reduced left-hemispheric language dominance. Here, we investigated, whether different polymorphisms in GRIN2B influence language lateralization and handedness in healthy individuals. In a cohort of 424 genetically unrelated participants we found significant association between the synonymous GRIN2B variation rs1806201 and language lateralization assessed using the dichotic listening task. Individuals carrying the heterozygous CT genotype exhibited more pronounced left-hemispheric language dominance as compared to both homozygous CC and TT individuals. Such an association was not identified for handedness. These findings suggest that variation in NMDA-receptors contributes to the interindividual variability of language lateralization.

Is Functional MR Imaging Assessment of Hemispheric Language Dominance as Good as the Wada Test?: A Meta-Analysis

To perform a systematic review and meta-analysis to quantitatively assess functional magnetic resonance (MR) imaging lateralization of language function in comparison with the Wada test. This study was determined to be exempt from review by the institutional review board. A systematic review and meta-analysis were performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A structured Medline search was conducted to identify all studies that compared functional MR imaging with the Wada test for determining hemispheric language dominance prior to brain surgery. Studies meeting predetermined inclusion criteria were selected independently by two radiologists who also assessed their quality using the Quality Assessment of Diagnostic Accuracy Studies tool. Language dominance was classified as typical (left hemispheric language dominance) or atypical (right hemispheric language dominance or bilateral language representation) for each patient. A meta-analysis was then performed by using a bivariate random-effects model to derive estimates of sensitivity and specificity, with Wada as the standard of reference. Subgroup analyses were also performed to compare the different functional MR imaging techniques utilized by the studies. Twenty-three studies, comprising 442 patients, met inclusion criteria. The sensitivity and specificity of functional MR imaging for atypical language dominance (compared with the Wada test) were 83.5% (95% confidence interval: 80.2%, 86.7%) and 88.1% (95% confidence interval: 87.0%, 89.2%), respectively. Functional MR imaging provides an excellent, noninvasive alternative for language lateralization and should be considered for the initial preoperative assessment of hemispheric language dominance. Further research may help determine which functional MR methods are most accurate for specific patient populations.

Hemisphere lateralization is influenced by bilingual status and composition of words

It has been generally accepted that the left hemisphere is more functionally specialized for language than the right hemisphere for right-handed monolinguals. But more and more studies have also demonstrated right hemisphere advantage for some language tasks with certain participants. A recent comprehensive survey has shown that hemisphere lateralization of language depends on the bilingual status of the participants, with bilateral hemispheric involvement for both languages of early bilinguals, who acquired both languages by age of 6, left hemisphere dominance for language of monolinguals, and also left hemisphere dominance for both languages of late bilinguals, who acquired the second language after age of 6. We propose a preliminary model which takes into account both composition of stimulus words and bilingual status of participants to resolve the apparent controversies regarding hemisphere lateralization of various reading experiments in the literature with focus on Chinese characters, and to predict lateralization patterns for future experiments in Chinese word reading. The bilingual status includes early bilingual, late bilingual and monolingual. However, we have tested this model only with late Chinese–English bilingual participants by using a Stroop paradigm in this paper, though the aim of our model is to disentangle the controversies in the lateralization effect of Chinese character reading. We show here with stimuli written in Chinese single characters that the Stroop effect was stronger when the stimuli were presented to the right than to the left visual field, implying that the language information and color identification/naming may interact more strongly in the left hemisphere. Therefore, our experimental results indicate left hemisphere dominance for Chinese character processing, providing evidence for one part of our model.

Regional variation, hemispheric asymmetries and gender differences in pericortical white matter

Brain white matter tissue composition can be quantified using Diffusion Tensor Imaging (DTI) and Magnetization Transfer Imaging (MTI). Fractional Anisotropy (FA), derived from DTI, indexes the integrity, density and organization of axons. Magnetization Transfer Ratio (MTR), derived from MTI, indexes to the presence of cell membranes and myelin. The combined use of FA and MTR provides a more complete picture of white matter structure than either imaging modality in isolation. Here we describe the regional distribution of FA and MTR measurements of pericortical white matter in 56 young, healthy right-handed subjects. Significant regional and lobar differences are seen for both measures along with a significant gender difference in FA. Highly consistent hemispheric asymmetries in FA and MTR were observed, suggesting that the greater fiber coherence and increased myelination of fibers in left hemisphere perisylvian regions may provide a structural basis for left-hemisphere language dominance.

Atypical lateralization of language predicts cerebral asymmetries in parietal gesture representations

Humans typically show left-hemisphere dominance both for language and manual gestures. If this reflects a dependence of these behaviors on a common cerebral specialization, then healthy left-handers with atypical organization of language should show a similar pattern for gesture. Consistent with this hypothesis, we report fMRI data indicating that sinistrals (5/15) with bilateral, or right-lateralized, language representations in inferior frontal cortex exhibit a similar atypical pattern in inferior parietal representations of familiar gestures.

Differential effects of prenatal testosterone on lateralization of handedness and language.

Handedness is the most noticeable functional expression of cerebral lateralization in humans. However, its developmental process and plasticity remain elusive. It has been postulated that prenatal testosterone (pT) has an effect on human lateralization development. In the present study we examined the relationship between pT and handedness and compared the outcome to previously published data on language lateralization in the same children. pT was assessed from amniotic fluid of healthy pregnant women using radioimmunoassay. Strength and direction of handedness of the children (n = 65 [31 girls, 34 boys], mean age [years]: 6.43, range: 5.97-7.53) was assessed based on hand choice during performance of age appropriate tasks. Regression procedures and the Olkin & Siotani Z-statistic were used. Results demonstrate that higher pT exposure was related to a decrease in strength of handedness (R² = .11, p = .01). The analysis shows that pT has quite stronger explanatory power than sex by itself, although there may be an additional effect of sex independent from pT. In a subgroup of these children we recently reported that higher levels of pT are related to increased left hemisphere dominance for language. Analyses show that pT is differentially related to handedness and language lateralization in these children (Z > 2.75, p < .003). Results imply a differential effect of pT on language lateralization and handedness. This may be explained by differential sensitivity of different areas of the corpus callosum or hemispheres for androgens, fuelling the ongoing debate about the relationship between prenatal exposure to testosterone and lateralization of brain and behavior.