Lesion characteristics driving right-hemispheric language reorganization in congenital left-hemispheric brain damage

The long-term negative impact of childhood stroke on language

Objectives

This study aims to investigate the long-term language outcome in children with unilateral childhood stroke in comparison to those with perinatal strokes and typically developing individuals and to explore the impact of lesion-specific modifiers.

Methods

We examined nine patients with childhood stroke, acquired between 0;2 and 16;1 years (CHILD; 3 female, median = 13.5 years, 6 left-sided), 23 patients with perinatal strokes (PERI; 11 female, median = 12.5 years, 16 left-sided), and 33 age-matched typically developing individuals (CONTROL; 15 female, median = 12.33 years). The language outcome was assessed using age-appropriate tasks of the Potsdam Illinois Test of Psycholinguistic Abilities (P-ITPA) or the Peabody Picture Vocabulary Test (PPVT). For group comparisons, study-specific language z-scores were calculated. Non-verbal intelligence was assessed using the Test of Non-verbal Intelligence (TONI-4), language lateralization with functional MRI, and lesion size with MRI-based volumetry.

Results

All four patients with childhood stroke who initially presented with aphasic symptoms recovered from aphasia. Patients with childhood stroke showed significantly lower language scores than those in the control group, but their scores were similar to those of the patients with perinatal stroke, after adjusting for general intelligence (ANCOVA, language z-score CHILD = -0.30, PERI = -0.38, CONTROL = 0.42). Among the patients with childhood stroke, none of the possible modifying factors, including lesion side, correlated significantly with the language outcome.

Conclusion

Childhood stroke, regardless of the affected hemisphere, can lead to chronic language deficits, even though affected children show a "full recovery." The rehabilitation of children and adolescents with childhood stroke should address language abilities, even after the usually quick resolution of clear aphasic symptoms.

Cerebellar Mutism Syndrome and Dentato-Thalamo-Cortical Tract Disruption in Diffusion Tractography Following Surgery for Medulloblastoma

Background Cerebellar mutism syndrome (CMS), a complication following medulloblastoma surgery, has been linked to dentato-thalamo-cortical tract (DTCT) injury; the association of the degree of DTCT injury with severity of CMS-related symptoms has not been investigated. Purpose To investigate the association between severity of CMS-related symptoms and degree and patterns of DTCT injury with use of diffusion tensor imaging (DTI), and if laterality of injury influences neurologic symptoms. Materials and Methods This retrospective case-control study used prospectively collected clinical and DTI data on patients with medulloblastoma enrolled in a clinical trial (between July 2016 and February 2020) and healthy controls (between April and November 2017), matched with the age range of the participants with medulloblastoma. CMS was divided into types 1 (CMS1) and 2 (CMS2). Multivariable logistic regression was used to investigate the relationship between CMS likelihood and DTCT injury. Results Overall, 82 participants with medulloblastoma (mean age, 11.0 years ± 5.2 [SD]; 53 male) and 35 healthy controls (mean age, 18.0 years ± 3.06; 18 female) were included. In participants with medulloblastoma, DTCT was absent bilaterally (AB), absent on the right side (AR), absent on the left side (AL), or present bilaterally (PB), while it was PB in all healthy controls. Odds of having CMS were associated with higher degree of DTCT damage (AB, odds ratio = 272.7 [95% CI: 269.68, 275.75; P < .001]; AR, odds ratio = 14.40 [95% CI: 2.84, 101.48; P < .001]; and AL, odds ratio = 8.55 [95% CI: 1.15, 74.14; P < .001). Left (coefficient = -0.07, χ2 = 12.4, P < .001) and right (coefficient = -0.15, χ2 = 33.82, P < .001) DTCT volumes were negatively associated with the odds of CMS. More participants with medulloblastoma with AB showed CMS1; unilateral DTCT absence prevailed in CMS2. Lower DTCT volumes correlated with more severe ataxia. Unilateral DTCT injury caused ipsilateral dysmetria; AB caused symmetric dysmetria. PB indicated better neurologic outcome. Conclusion The severity of CMS-associated mutism, ataxia, and dysmetria was associated with DTCT damage severity. DTCT damage patterns differed between CMS1 and CMS2. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Dorigatti Soldatelli and Ertl-Wagner in this issue.

Language lateralization and outcome in perinatal stroke patients with different vascular types

Perinatal stroke affects child's language development and can change language lateralization. Language generation and comprehension tasks in functional magnetic resonance imaging were used to determine language lateralization in term born children with perinatal left-side arterial ischemic stroke (AIS) (n = 9, mean age (SD) 13.4 (3.1) y.) and periventricular venous infarction (PVI) (n = 12, 11.8 (2.8) y.), and in healthy right-handed controls (n = 30, 11.6 (2.6) y.). Lateralization index was calculated for the Broca and Wernicke areas and correlated with language and cognitive outcomes measured by the Kaufman Assessment Battery for Children II ed. Language outcome in children with perinatal stroke is poorer compared to healthy controls. Children with small AIS lesions and most children with PVI showed left-side language activation. Most children with large AIS lesions and one child with large PVI had language activation reorganized to the right hemisphere. Language reorganization to the unlesioned right hemisphere did not ensure normal language outcome.

Cognitive development after perinatal unilateral infarctions: No evidence for preferential sparing of verbal functions

BACKGROUND

Even children with extensive perinatal left-sided lesions have been reported to show normal language functions based on right-hemispheric language reorganization. This reorganization can lead to deficits in originary right hemispheric functions ("crowding hypothesis"). In a previous study, however, we identified epilepsy (even when well-controlled), and not language reorganization, as the major risk factor for impaired nonverbal functions. Here, we asked whether verbal and nonverbal functions develop differently, and whether they share the same risk factors.

METHODS

We investigated 23 patients (11f, Md = 12.56 years) with perinatal strokes (16 left-sided, 8 with epilepsy), and 23 healthy age-matched controls (8 f, Md = 12.42years). Language functions were assessed using the Potsdam Illinois Test of Psycholinguistic Abilities, nonverbal intelligence with the Test of Nonverbal Intelligence, language lateralization with functional MRI, and lesion size with MRI-based volumetry.

RESULTS

We found no systematic difference between verbal and nonverbal skills in our patients or controls [median difference Z(PITPA)-Z(TONI): patients = -0.03, controls = -0.06]. Accordingly, verbal and nonverbal functions were strongly correlated in patients (r = 0.80) and in controls (r = 0.74). Language ability correlated significantly with epilepsy. Furthermore, in patients with epilepsies, verbal skills were significantly lower than in controls.

CONCLUSION

In our cohort, we found no evidence for a differential effect of perinatal strokes on the development of verbal versus nonverbal functions, and, specifically, no evidence for a preferential sparing of verbal functions. Epilepsy, even when well-controlled, was confirmed as a single key risk factor for verbal functions.

Neonatal arterial stroke location is associated with outcome at 2 years: a voxel-based lesion-symptom mapping study

OBJECTIVE

In contrast to motor impairments, the association between lesion location and cognitive or language deficits in patients with neonatal arterial ischaemic stroke remains largely unknown. We conducted a voxel-based lesion-symptom mapping cross-sectional study aiming to reveal neonatal arterial stroke location correlates of language, motor and cognitive outcomes at 2 years of age.

DESIGN

Prospective observational multicentre study.

SETTING

Six paediatric university hospitals in Spain.

PARTICIPANTS

We included 53 patients who had a neonatal arterial ischaemic stroke with neonatal MRI and who were followed up till 2 years of age.

MAIN OUTCOME MEASURES

We analysed five dichotomous clinical variables: speech therapy (defined as the need for speech therapy as established by therapists), gross motor function impairment, and the language, motor and cognitive Bayley scales. All the analyses were controlled for total lesion volume.

RESULTS

We found that three of the clinical variables analysed significantly correlated with neonatal stroke location. Speech therapy was associated with lesions located mainly at the left supramarginal gyrus (p=0.007), gross motor function impairment correlated with lesions at the left external capsule (p=0.044) and cognitive impairment was associated with frontal lesions, particularly located at the left inferior and middle frontal gyri (p=0.012).

CONCLUSIONS

The identification of these susceptible brain areas will allow for more precise prediction of neurological impairments on the basis of neonatal brain MRI.

Impact of Brain Functional Network Properties on Intelligence in Children and Adolescents with Focal Epilepsy: A Resting-state MRI Study

RATIONALE AND OBJECTIVE

Epilepsy is a common pediatric disease that often leads to cognitive and intellectual impairments. Here, we explore the reorganized functional networks in children and adolescents with focal epilepsy (CAFE) and analyze the relationship between network reorganization and intellectual deficits to reveal the underlying link between them.

MATERIALS AND METHODS

Fifty-four CAFE (6-16 years old; right-handed) and 42 well-matched healthy controls were recruited. Subjects underwent resting-state functional magnetic resonance imaging, and functional networks were analyzed by graph analysis. Intelligence testing (Wechsler Intelligence Scale for Children-Chinese revision) included measures for verbal IQ (VIQ), performance IQ, and full-scale IQ.

RESULTS

(1) In the CAFE compared with the healthy controls, (a) the local efficiency, clustering coefficient and standardized clustering coefficient were significantly decreased (p < 0.05); (b) the degree centrality and nodal efficiency of the left precentral gyrus (LPG) were significantly increased (p < 0.05, Bonferroni correction), and the nodal shortest path length was significantly decreased (p < 0.05, Bonferroni correction); and (c) functional connectivity of the LPG with the bilateral inferior frontal ventral gyrus, right lateral superior occipital gyrus, left middle occipital gyrus, bilateral superior parietal lobule, right anterior prefrontal cortex, and bilateral cerebellum was enhanced (p < 0.05,GRF correction), while functional connectivity with the bilateral superior temporal gyrus was decreased (p < 0.05, GRF correction). (2) The nodal shortest path length of the LPG in CAFE was associated with full-scale IQ, performance IQ, and VIQ, and local efficiency was associated with VIQ.

CONCLUSION

Our results showed that the middle LPG in CAFE undergoes network reorganization that positively influences intelligence. Differences in local efficiency of functional networks in children and early adolescents have a significant effect on intelligence.

Effect of corpus callosum agenesis on the language network in children and adolescents

The present study is interested in the role of the corpus callosum in the development of the language network. We, therefore, investigated language abilities and the language network using task-based fMRI in three cases of complete agenesis of the corpus callosum (ACC), three cases of partial ACC and six controls. Although the children with complete ACC revealed impaired functions in specific language domains, no child with partial ACC showed a test score below average. As a group, ACC children performed significantly worse than healthy controls in verbal fluency and naming. Furthermore, whole-brain ROI-to-ROI connectivity analyses revealed reduced intrahemispheric and right intrahemispheric functional connectivity in ACC patients as compared to controls. In addition, stronger functional connectivity between left and right temporal areas was associated with better language abilities in the ACC group. In healthy controls, no association between language abilities and connectivity was found. Our results show that ACC is associated not only with less interhemispheric, but also with less right intrahemispheric language network connectivity in line with reduced verbal abilities. The present study, thus, supports the excitatory role of the corpus callosum in functional language network connectivity and language abilities.

Non-verbal Intelligence in Unilateral Perinatal Stroke Patients With and Without Epilepsies

Background: The risk factors for impaired cognitive development after unilateral perinatal stroke are poorly understood. Non-verbal intelligence seems to be at particular risk, since language can shift to the right hemisphere and may thereby reduce the capacity of the right hemisphere for its originary functions. Pharmaco-refractory epilepsies, a frequent complication of perinatal strokes, often lead to impaired intelligence. Yet, the role of well-controlled epilepsies is less well-understood. Here, we investigated whether well-controlled epilepsies, motor impairment, lesion size, lesion side, and lateralization of language functions influence non-verbal functions. Methods: We recruited 8 patients with well-controlled epilepsies (9-26 years), 15 patients without epilepsies (8-23 years), and 23 healthy controls (8-27 years). All underwent the Test of Non-verbal Intelligence, a motor-independent test, which excludes biased results due to motor impairment. Language lateralization was determined with functional MRI, lesion size with MRI-based volumetry, and hand motor impairment with the Jebson-Taylor Hand Function-Test. Results: Patients with epilepsies showed significantly impaired non-verbal intelligence [Md = 89.5, interquartile range (IQR) = 13.5] compared with controls (Md = 103, IQR = 17). In contrast, patients without epilepsies (Md = 97, IQR = 15.0) performed within the range of typically developing children. A multiple regression analysis revealed only epilepsy as a significant risk factor for impaired non-verbal functions. Conclusion: In patients with unilateral perinatal strokes without epilepsies, the neuroplastic potential of one healthy hemisphere is able to support the development of normal non-verbal cognitive abilities, regardless of lesion size, lesion side, or language lateralization. In contrast, epilepsy substantially reduces this neuroplastic potential; even seizure-free patients exhibit below-average non-verbal cognitive functions.

Signatures of brain plasticity supporting language recovery after perinatal arterial ischemic stroke

Brain imaging methods such as functional Magnetic Resonance Imaging (fMRI) and Diffusion Tensor Imaging (DTI) have already been used to decipher the functional and structural brain changes occurring during normal language development. However, little is known about the differentiation of the language network after an early lesion. While in adults, stroke over the left hemisphere generally induces post-stroke aphasia, it is not always the case when a stroke occurs in the perinatal period, thus revealing a remarkable plastic power of the language network during early development. In particular, the role of perilesional tissues, as opposed to undamaged brain areas in the functional recovery of language functions after an early insult, remains unclear. In this review article, we provide an overview of the extant literature using functional and structural neuroimaging data revealing the signatures of brain plasticity underlying near-normal language development.

Exploring the neural correlates of self-related names in healthy subjects

OBJECTIVES

This study aimed to clarify the neural correlates and underlying mechanisms of the subject's own name (SON) and the unique name derived from the SON (SDN).

METHODS

A name that was most familiar to the subject (SFN) was added as a self-related reference. We used 4 auditory stimuli-pure tone (1000 Hz), SON, SDN, and SFN-to evaluate the corresponding activated brain areas in 19 healthy subjects by using functional magnetic resonance imaging.

RESULTS

Our results demonstrated that pure tone activated the fewest brain regions. Although SFN was a very strong self-related stimulus, it failed to activate many midline structures. The brain regions activated by SON and SDN were very similar. SFN as a self-related stimulus was less self-related compared with SDN. What's more, the additionally activated fusiform gyrus and parahippocampal gyrus of SDN might revealed its processing path.

CONCLUSIONS

SDN, which has created by us, is a new and self-related stimulus similar to SON. They might provide a useful reference for consciousness assessment with SON and SDN.

Principles of early intervention

The great majority of children with neurodevelopmental challenges do not get specific intervention until after their second birthday. This worsens their outcomes, because a great part of the entire neuroplastic window for learning is misspent. There is emerging evidence that the impact on outcomes of early goal-directed training involving the parents in infants with neurodevelopmental disabilities is significantly superior to the results achieved in older children and adults, especially if intervention commences in the first months of life. This chapter outlines the common elements of neurodevelopment and early intervention. It includes an outline of some of the primary early intervention practices and the scientific evidence driving them.

Patterns and predictors of language representation and the influence of epilepsy surgery on language reorganization in children and young adults with focal lesional epilepsy

Mapping brain functions is crucial for neurosurgical planning in patients with drug-resistant seizures. However, presurgical language mapping using either functional or structural networks can be challenging, especially in children. In fact, most of the evidence on this topic derives from cross-sectional or retrospective studies in adults submitted to anterior temporal lobectomy. In this prospective study, we used fMRI and DTI to explore patterns of language representation, their predictors and impact on cognitive performances in 29 children and young adults (mean age at surgery: 14.6 ± 4.5 years) with focal lesional epilepsy. In 20 of them, we also assessed the influence of epilepsy surgery on language lateralization. All patients were consecutively enrolled at a single epilepsy surgery center between 2009 and 2015 and assessed with preoperative structural and functional 3T brain MRI during three language tasks: Word Generation (WG), Rhyme Generation (RG) and a comprehension task. We also acquired DTI data on arcuate fasciculus in 24 patients. We first assessed patterns of language representation (relationship of activations with the epileptogenic lesion and Laterality Index (LI)) and then hypothesized a causal model to test whether selected clinical variables would influence the patterns of language representation and the ensuing impact of the latter on cognitive performances. Twenty out of 29 patients also underwent postoperative language fMRI. We analyzed possible changes of fMRI and DTI LIs and their clinical predictors. Preoperatively, we found atypical language lateralization in four patients during WG task, in one patient during RG task and in seven patients during the comprehension task. Diffuse interictal EEG abnormalities predicted a more atypical language representation on fMRI (p = 0.012), which in turn correlated with lower attention (p = 0.036) and IQ/GDQ scores (p = 0.014). Postoperative language reorganization implied shifting towards atypical language representation. Abnormal postoperative EEG (p = 0.003) and surgical failures (p = 0.015) were associated with more atypical language lateralization, in turn correlating with worsened fluency. Neither preoperative asymmetry nor postoperative DTI LI changes in the arcuate fasciculus were observed. Focal lesional epilepsy associated with diffuse EEG abnormalities may favor atypical language lateralization and worse cognitive performances, which are potentially reversible after successful surgery.

Predicting Language Outcome After Left Hemispherotomy: A Systematic Literature Review

Objective

Hemidecortication is a therapeutic option in patients with drug-resistant structural epilepsy. If surgery is performed early enough in left-hemispheric pathology, the plasticity of the developing brain may enable the right hemisphere to take over language-if this has not occurred before surgery. A systematic overview of potential predictors of language outcome after left hemidecortication in children is warranted.

Methods

In a systematic literature review, we analyzed 58 studies on language lateralization after congenital or postneonatally acquired left-hemispheric pathology, and on language outcome after left-sided hemidisconnection, such as hemispherotomy. Single-subject data were pooled to determine the distribution of lateralization across etiologies in congenital lesions and across age groups in acute postneonatal lesions. A hierarchical linear regression assessed the influence of age at surgery, lesion type, age at seizure onset, and presurgery language function on language outcome after left hemidecortication.

Results

In acute postneonatal lesions, younger age at injury was significantly associated with right-sided language lateralization (Cramér V = 0.458; p = 0.039). In patients with hemidecortication, age at surgery was not significantly associated with language outcome (Cramér V = -0.056; p = 0.584). Presurgical language function was the most powerful predictor for postsurgical language outcome (F _4,47 = 7.35, p < 0.0001), with good presurgical language bearing the risk of postsurgical deterioration. In congenital pathology, right-sided language lateralization was most frequent in pre-/perinatal stroke (Cramér V = 0.357; p < 0.0001).

Conclusions

We propose a presurgical decision algorithm with age, presurgical language function, language lateralization, and left-hemispheric structural pathology as decision points regarding surgery.

Cortical stimulation mapping for localization of visual and auditory language in pediatric epilepsy patients

OBJECTIVE

To determine resection margins near eloquent tissue, electrical cortical stimulation (ECS) mapping is often used with visual naming tasks. In recent years, auditory naming tasks have been found to provide a more comprehensive map. Differences in modality-specific language sites have been found in adult patients, but there is a paucity of research on ECS language studies in pediatric patients. The goals of this study were to evaluate word-finding distinctions between visual and auditory modalities and identify which cortical subregions most often contain critical language function in a pediatric population.

METHODS

Twenty-one pediatric patients with epilepsy or temporal lobe pathology underwent ECS mapping using visual (n = 21) and auditory (n = 14) tasks. Fisher's exact test was used to determine whether the frequency of errors in the stimulated trials was greater than the patient's baseline error rate for each tested modality and subregion.

RESULTS

While the medial superior temporal gyrus was a common language site for both visual and auditory language (43.8% and 46.2% of patients, respectively), other subregions showed significant differences between modalities, and there was significant variability between patients. Visual language was more likely to be located in the anterior temporal lobe than was auditory language. The pediatric patients exhibited fewer parietal language sites and a larger range of sites overall than did adult patients in previously published studies.

CONCLUSIONS

There was no single area critical for language in more than 50% of patients tested in either modality for which more than 1 patient was tested (n > 1), affirming that language function is plastic in the setting of dominant-hemisphere pathology. The high rates of language function throughout the left frontal, temporal, and anterior parietal regions with few areas of overlap between modalities suggest that ECS mapping with both visual and auditory testing is necessary to obtain a comprehensive language map prior to epileptic focus or tumor resection.

Language Cerebro-cerebellar Reorganization in Children After Surgery of Right Cerebellar Astrocytoma: a fMRI Study

Language processing depends on an integrated circuit involving the left supratentorial language areas and the right posterior lateral cerebellar hemisphere (lobule VI, lobule VII, Crus I, and Crus II). Reorganization of the language system after lesions of the cerebral language areas includes also cerebellar relocation. This is the first study assessing functional language reorganization after lesions concerning primarily the cerebellum, using a fMRI paradigm of phonological covert word production task in six children operated for right cerebellar astrocytoma and in 15 typically developing children. We found right cerebellar and left frontal activations in healthy controls and high variability of reorganizational patterns in patients with early right cerebellar lesion. Also lesions not located in the areas typically involved in language tasks (Crus I and Crus II) can cause reorganization between the two hemispheres or hemispheric language reinforcement of the original lateralization. We discuss the role of several variables in determining the reorganizational pattern such as the site, extension, and timing of surgery. No variables revealed as predictors, suggesting that co-occurring influence of other biological and/or pathological factors are not yet demonstrated. Lesions in the postero-lateral cerebellum seem related to less efficient language performances, as an indicator of the system's functioning.

Right Structural and Functional Reorganization in Four-Year-Old Children with Perinatal Arterial Ischemic Stroke Predict Language Production

Brain imaging methods have contributed to shed light on the mechanisms of recovery after early brain insult. The assumption that the unaffected right hemisphere can take over language functions after left perinatal stroke is still under debate. Here, we report how patterns of brain structural and functional reorganization were associated with language outcomes in a group of four-year-old children with left perinatal arterial ischemic stroke (PAIS). Specifically, we gathered specific fine-grained developmental measures of receptive and productive aspects of language as well as standardized measures of cognitive development. We also collected structural neuroimaging data as well as functional activations during a passive listening story-telling fMRI task and a resting state session (rs-fMRI). Children with a left perinatal stroke showed larger lateralization indices of both structural and functional connectivity of the dorsal language pathway towards the right hemisphere that, in turn, were associated with better language outcomes. Importantly, the pattern of structural asymmetry was significantly more right-lateralized in children with a left perinatal brain insult than in a group of matched healthy controls. These results strongly suggest that early lesions of the left dorsal pathway and the associated perisylvian regions can induce the interhemispheric transfer of language functions to right homolog regions. This study provides combined evidence of structural and functional brain reorganization of language networks after early stroke with strong implications for neurobiological models of language development.

Developmental conduction aphasia after neonatal stroke

Objective

Impairment of speech repetition following injury to the dorsal language stream is a feature of conduction aphasia, a well‐described “disconnection syndrome” in adults. The impact of similar lesions sustained in infancy has not been established.

Methods

We compared language outcomes in term‐born individuals with confirmed neonatal stroke (n = 30, age = 7–18 years, left‐sided lesions in 21 cases) to matched controls (n = 40). Injury to the dorsal and/or ventral language streams was assessed using T₁‐ and T₂‐weighted magnetic resonance imaging (MRI) and diffusion tractography. Language lateralization was determined using functional MRI.

Results

At the group level, left dorsal language stream injury was associated with selective speech repetition impairment for nonwords (p = 0.021) and sentences (p < 0.0001). The majority of children with significant repetition impairment had retained left hemisphere language representation, but right hemisphere dominance was correlated with minimal or absent repetition deficits. Post hoc analysis of the repetition‐impaired group revealed additional language‐associated deficits, but these were more subtle and variable.

Interpretation

We conclude that (1) despite the considerable plasticity of the infant brain, early dorsal language stream injury can result in specific and long‐lasting problems with speech repetition that are similar to the syndrome of conduction aphasia seen in adults; and (2) language reorganization to the contralateral hemisphere has a protective effect. Ann Neurol 2018;83:664–675 Ann Neurol 2018;83:664–675

From Broca and Wernicke to the Neuromodulation Era: Insights of Brain Language Networks for Neurorehabilitation

Communication in humans activates almost every part of the brain. Of course, the use of language predominates, but other cognitive functions such as attention, memory, emotion, and executive processes are also involved. However, in order to explain how our brain "understands," "speaks," and "writes," and in order to rehabilitate aphasic disorders, neuroscience has faced the challenge for years to reveal the responsible neural networks. Broca and Wernicke (and Lichtheim and many others), during the 19th century, when brain research was mainly observational and autopsy driven, offered fundamental knowledge about the brain and language, so the Wernicke-Geschwind model appeared and aphasiology during the 20th century was based on it. This model is still useful for a first approach into the classical categorization of aphasic syndromes, but it is outdated, because it does not adequately describe the neural networks relevant for language, and it offers a modular perspective, focusing mainly on cortical structures. During the last three decades, neuroscience conquered new imaging, recording, and manipulation techniques for brain research, and a new model of the functional neuroanatomy of language was developed, the dual stream model, consisting of two interacting networks ("streams"), one ventral, bilaterally organized, for language comprehension, and one dorsal, left hemisphere dominant, for production. This new model also has its limitations but helps us to understand, among others, why patients with different brain lesions can have similar language impairments. Furthermore, interesting aspects arise from studying language functions in aging brains (and also in young, developing brains) and in cognitively impaired patients and neuromodulation effects on reorganization of brain networks subserving language. In this selective review, we discuss methods for coupling new knowledge regarding the functional reorganization of the brain with sophisticated techniques capable of activating the available supportive networks in order to provide improved neurorehabilitation strategies for people suffering from neurogenic communication disorders.

Functional connectivity of language networks after perinatal stroke

Successful language acquisition during development is imperative for lifelong function. Complex language networks develop throughout childhood. Perinatal stroke may cause significant language disabilities but function can also be remarkably normal. Studying such very early brain injury populations may inform developmental plasticity models of language networks. We examined functional connectivity (FC) of language networks in children with arterial and venous perinatal stroke and typically developing controls (TDC) in a population-based, controlled, cohort study. Resting state functional MRI was performed at 3 T (TR/TE = 2000/30 ms, 150 volumes, 3.6mm3 voxels). Seed-based analyses used bilateral inferior frontal and superior temporal gyri. A subset of stroke participants completed clinical language testing. Sixty-six children participated (median age: 12.85±3.8y, range 6-19; arterial N = 17; venous N = 15; TDC N = 34]. Children with left hemisphere strokes had comparable FC in their right hemispheres compared to TDC. Inter- and intra-hemispheric connectivity strengths were similar between TDC and PVI but lower for AIS. Reduced FC was associated with poorer language comprehension. Language networks can be estimated using resting-state fMRI in children with perinatal stroke. Altered connectivity may occur in both hemispheres, is more pronounced with arterial lesions, and is associated with clinical function. Our results have implications for therapeutic language interventions after early stroke.

Neuroscience and education: Cerebral lateralization of networks and oscillations in dyslexia

Liaison between neuroscience and education has resulted in significant advances in our understanding of the neurobiological learning requirements of individuals with reading disability, the neuroplasticity of the developing brain, and the participation of the right hemisphere in reading. Research in neural network theory and cortical oscillations suggests that the hemispheres collaborate in high-level language processes. The right hemisphere specializes in coding low frequencies of the speech envelope and interhemispheric cognitive control, while the left is specialized for local high frequency, verbal computations. Studies in neural networks, and cortical oscillations which controlled for reading-level, converge in identifying an impaired right hemisphere circuitry of frontoparietal attention networks as a primary cause of dyslexia. Occurring in early development, such a dysfunction would have a cascading negative effect on phonemic processing in the left hemisphere dorsal reading network. Such integrative hemispheric cooperation suggests a more comprehensive approach to early reading instruction and interventions in dyslexia.

Corticobulbar Tract Injury, Oromotor Impairment and Language Plasticity in Adolescents Born Preterm

Children born preterm are at risk of impairments in oromotor control, with implications for early feeding and speech development. In this study, we aimed to identify (a) neuroanatomical markers of persistent oromotor deficits using diffusion-weighted imaging (DWI) tractography and (b) evidence of compensatory neuroplasticity using functional MRI (fMRI) during a language production task. In a cross-sectional study of 36 adolescents born very preterm (<33 weeks' gestation) we identified persistent difficulties in oromotor control in 31% of cases, but no clinical diagnoses of speech-sound disorder (e.g., dysarthria, dyspraxia). We used DWI-tractography to examine the microstructure (fractional anisotropy, FA) of the corticospinal and corticobulbar tracts. Compared to the unimpaired group, the oromotor-impaired group showed (i) reduced FA within the dorsal portion of the left corticobulbar tract (containing fibres associated with movements of the lips, tongue, and larynx) and (ii) greater recruitment of right hemisphere language regions on fMRI. We conclude that, despite the development of apparently normal everyday speech, early injury to the corticobulbar tract leads to persistent subclinical problems with voluntary control of the face, lips, jaw, and tongue. Furthermore, we speculate that early speech problems may be ameliorated by cerebral plasticity - in particular, recruitment of right hemisphere language areas.

Perilesional and homotopic area activation during proverb comprehension after stroke

INTRODUCTION

The mechanism of functional recovery in right hemisphere (RH) stroke patients when attempting to comprehend a proverb has not been identified. We previously reported that there is bilateral hemisphere involvement during proverb comprehension in the normal population. However, the underlying mechanisms of proverb comprehension following a right middle cerebral artery (MCA) infarction have not yet been fully elucidated.

METHODS

We here compared the brain regions activated by literal sentences and by opaque or transparent proverbs in right MCA infarction patients using functional magnetic resonance imaging (fMRI). Experimental stimuli included 18 opaque proverbs, 18 transparent proverbs, and 18 literal sentences that were presented pseudorandomly in 1 of 3 predesigned sequences.

RESULTS

Fifteen normal adults and 17 right MCA infarction patients participated in this study. The areas of the brain in the stroke patients involved in understanding a proverb compared with a literal sentence included the right middle frontal gyrus (MFG) and frontal pole, right anterior cingulate gyrus/paracingulate gyrus and left inferior frontal gyrus (IFG), middle temporal gyrus (MTG), precuneus, and supramarginal gyrus (SMG). When the proverbs were presented to these stroke patients in the comprehension tests, the left supramarginal, postcentral gyrus, and right paracingulate gyrus were activated for the opaque proverbs compared to the transparent proverbs.

CONCLUSIONS

These findings suggest that the functional recovery of language in stroke patients can be explained by perilesional activation, which is thought to arise from the regulation of the excitatory and inhibitory neurotransmitter system, and by homotopic area activation which has been characterized by decreased transcallosal inhibition and astrocyte involvement.

When two are better than one: Bilateral mesial temporal lobe contributions associated with better vocabulary skills in children and adolescents

This study considered the involvement of the mesial temporal lobe (MTL) in language and verbal memory functions in healthy children and adolescents. We investigated 30 healthy, right-handed children and adolescents, aged 7-16, with a fMRI language paradigm and a comprehensive cognitive test battery. We found significant MTL activations during language fMRI in all participants; 63% of them had left lateralized MTL activations, 20% exhibited right MTL lateralization, and 17% showed bilateral MTL involvement during the fMRI language paradigm. Group analyses demonstrated a strong negative correlation between the lateralization of MTL activations and language functions. Specifically, children with less lateralized MTL activation showed significantly better vocabulary skills. These findings suggest that the mesial temporal lobes of both hemispheres play an important role in language functioning, even in right-handers. Our results furthermore show that bilateral mesial temporal lobe involvement is advantageous for vocabulary skills in healthy, right-handed children and adolescents.