White matter plasticity during second language learning within and across hemispheres.

Adult second language (L2) learning is a challenging enterprise inducing neuroplastic changes in the human brain. However, it remains unclear how the structural language connectome and its subnetworks change during adult L2 learning. The current study investigated longitudinal changes in white matter (WM) language networks in each hemisphere, as well as their interconnection, in a large group of Arabic-speaking adults who learned German intensively for 6 mo. We found a significant increase in WM-connectivity within bilateral temporal-parietal semantic and phonological subnetworks and right temporal-frontal pathways mainly in the second half of the learning period. At the same time, WM-connectivity between the two hemispheres decreased significantly. Crucially, these changes in WM-connectivity are correlated with L2 performance. The observed changes in subnetworks of the two hemispheres suggest a network reconfiguration due to lexical learning. The reduced interhemispheric connectivity may indicate a key role of the corpus callosum in L2 learning by reducing the inhibition of the language-dominant left hemisphere. Our study highlights the dynamic changes within and across hemispheres in adult language-related networks driven by L2 learning.

Native language differences in the structural connectome of the human brain.

Is the neuroanatomy of the language structural connectome modulated by the life-long experience of speaking a specific language? The current study compared the brain white matter connections of the language and speech production network in a large cohort of 94 native speakers of two very different languages: an Indo-European morphosyntactically complex language (German) and a Semitic root-based language (Arabic). Using high-resolution diffusion-weighted MRI and tractography-based network statistics of the language connectome, we demonstrated that German native speakers exhibited stronger connectivity in an intra-hemispheric frontal to parietal/temporal dorsal language network, known to be associated with complex syntax processing. In comparison, Arabic native speakers showed stronger connectivity in the connections between semantic language regions, including the left temporo-parietal network, and stronger inter-hemispheric connections via the posterior corpus callosum connecting bilateral superior temporal and inferior parietal regions. The current study suggests that the structural language connectome develops and is modulated by environmental factors such as the characteristic processing demands of the native language.

Children's syntax is supported by the maturation of BA44 at 4 years, but of the posterior STS at 3 years of age.

Within the first years of life, children learn major aspects of their native language. However, the ability to process complex sentence structures, a core faculty in human language called syntax, emerges only slowly. A milestone in syntax acquisition is reached around the age of 4 years, when children learn a variety of syntactic concepts. Here, we ask which maturational changes in the child's brain underlie the emergence of syntactically complex sentence processing around this critical age. We relate markers of cortical brain maturation to 3- and 4-year-olds' sentence processing in contrast to other language abilities. Our results show that distinct cortical brain areas support sentence processing in the two age groups. Sentence production abilities at 3 years were associated with increased surface area in the most posterior part of the left superior temporal sulcus, whereas 4-year-olds showed an association with cortical thickness in the left posterior part of Broca's area, i.e. BA44. The present findings suggest that sentence processing abilities rely on the maturation of distinct cortical regions in 3- compared to 4-year-olds. The observed shift to more mature regions involved in processing syntactically complex sentences may underlie behavioral milestones in syntax acquisition at around 4 years.

Differential contributions of inferior frontal gyrus subregions to sentence processing guided by intonation.

Auditory sentence comprehension involves processing content (semantics), grammar (syntax), and intonation (prosody). The left inferior frontal gyrus (IFG) is involved in sentence comprehension guided by these different cues, with neuroimaging studies preferentially locating syntactic and semantic processing in separate IFG subregions. However, this regional specialisation has not been confirmed with a neurostimulation method. Consequently, the causal role of such a specialisation remains unclear. This study probed the role of the posterior IFG (pIFG) for syntactic processing and the anterior IFG (aIFG) for semantic processing with repetitive transcranial magnetic stimulation (rTMS) in a task that required the interpretation of the sentence's prosodic realisation. Healthy participants performed a sentence completion task with syntactic and semantic decisions, while receiving 10 Hz rTMS over either left aIFG, pIFG, or vertex (control). Initial behavioural analyses showed an inhibitory effect on accuracy without task-specificity. However, electric field simulations revealed differential effects for both subregions. In the aIFG, stronger stimulation led to slower semantic processing, with no effect of pIFG stimulation. In contrast, we found a facilitatory effect on syntactic processing in both aIFG and pIFG, where higher stimulation strength was related to faster responses. Our results provide first evidence for the functional relevance of left aIFG in semantic processing guided by intonation. The stimulation effect on syntactic responses emphasises the importance of the IFG for syntax processing, without supporting the hypothesis of a pIFG-specific involvement. Together, the results support the notion of functionally specialised IFG subregions for diverse but fundamental cues for language processing.

Pitch accents create dissociable syntactic and semantic expectations during sentence processing.

The language system uses syntactic, semantic, as well as prosodic cues to efficiently guide auditory sentence comprehension. Prosodic cues, such as pitch accents, can build expectations about upcoming sentence elements. This study investigates to what extent syntactic and semantic expectations generated by pitch accents can be dissociated and if so, which cues take precedence when contradictory information is present. We used sentences in which one out of two nominal constituents was placed in contrastive focus with a third one. All noun phrases carried overt syntactic information (case-marking of the determiner) and semantic information (typicality of the thematic role of the noun). Two experiments (a sentence comprehension and a sentence completion task) show that focus, marked by pitch accents, established expectations in both syntactic and semantic domains. However, only the syntactic expectations, when violated, were strong enough to interfere with sentence comprehension. Furthermore, when contradictory cues occurred in the same sentence, the local syntactic cue (case-marking) took precedence over the semantic cue (thematic role), and overwrote previous information cued by prosody. The findings indicate that during auditory sentence comprehension the processing system integrates different sources of information for argument role assignment, yet primarily relies on syntactic information.

Hierarchical syntactic processing is beyond mere associating: Functional magnetic resonance imaging evidence from a novel artificial grammar.

Grammar is central to any natural language. In the past decades, the artificial grammar of the An Bn type in which a pair of associated elements can be nested in the other pair was considered as a desirable model to mimic human language syntax without semantic interference. However, such a grammar relies on mere associating mechanisms, thus insufficient to reflect the hierarchical nature of human syntax. Here, we test how the brain imposes syntactic hierarchies according to the category relations on linearized sequences by designing a novel artificial "Hierarchical syntactic structure-building Grammar" (HG), and compare this to the An Bn grammar as a "Nested associating Grammar" (NG) based on multilevel associations. Thirty-six healthy German native speakers were randomly assigned to one of the two grammars. Both groups performed a grammaticality judgment task on auditorily presented word sequences generated by the corresponding grammar in the scanner after a successful explicit behavioral learning session. Compared to the NG group, we found that the HG group showed a (a) significantly higher involvement of Brodmann area (BA) 44 in Broca's area and the posterior superior temporal gyrus (pSTG); and (b) qualitatively distinct connectivity between the two regions. Thus, the present study demonstrates that the build-up process of syntactic hierarchies on the basis of category relations critically relies on a distinctive left-hemispheric syntactic network involving BA 44 and pSTG. This indicates that our novel artificial grammar can constitute a suitable experimental tool to investigate syntax-specific processes in the human brain.

Intonation guides sentence processing in the left inferior frontal gyrus.

Speech prosody, the variation in sentence melody and rhythm, plays a crucial role in sentence comprehension. Specifically, changes in intonational pitch along a sentence can affect our understanding of who did what to whom. To date, it remains unclear how the brain processes this particular use of intonation and which brain regions are involved. In particular, one central matter of debate concerns the lateralisation of intonation processing. To study the role of intonation in sentence comprehension, we designed a functional magnetic resonance imaging (MRI) experiment in which participants listened to spoken sentences. Critically, the interpretation of these sentences depended on either intonational or grammatical cues. Our results showed stronger functional activity in the left inferior frontal gyrus (IFG) when the intonational cue was crucial for sentence comprehension compared to when it was not. When instead a grammatical cue was crucial for sentence comprehension, we found involvement of an overlapping region in the left IFG, as well as in a posterior temporal region. A further analysis revealed that the lateralisation of intonation processing depends on its role in syntactic processing: activity in the IFG was lateralised to the left hemisphere when intonation was the only source of information to comprehend the sentence. In contrast, activity in the IFG was right-lateralised when intonation did not contribute to sentence comprehension. Together, these results emphasise the key role of the left IFG in sentence comprehension, showing the importance of this region when intonation establishes sentence structure. Furthermore, our results provide evidence for the theory that the lateralisation of prosodic processing is modulated by its linguistic role.

The language skeleton after dissecting meaning: A functional segregation within Broca's Area.

Broca's area is proposed as a crucial brain area for linguistic computations. Language processing goes beyond word-level processing, also implying the integration of meaningful information (semantics) with the underlying structural skeleton (syntax). There is an on-going debate about the specialisation of the subregions of Broca's area-Brodmann areas (BA) 44 and 45-regarding the latter aspects. Here, we tested if syntactic information is specifically processed in BA 44, whereas BA 45 is mainly recruited for semantic processing. We contrasted conditions with sentence structure against conditions with random order in two fMRI experiments. Besides, in order to disentangle these processes, we systematically removed the amount of semantic information available in the stimuli. This was achieved in Experiment 1 by replacing meaningful words (content words) by pseudowords. Within real word conditions we found broad activation in the left hemisphere, including the inferior frontal gyrus (BA 44/45/47), the anterior temporal lobe and posterior superior temporal gyrus (pSTG) and sulcus (pSTS). For pseudowords we found a similar activation pattern, still involving BA 45. Among the pseudowords in Experiment 1, we kept those word elements that convey meaning like un- in unhappy or -hood in brotherhood (i.e. derivational morphology). In Experiment 2 we tested whether the activation in BA 45 was due to their presence. We therefore further removed derivational morphology, only leaving word elements that determine syntactic structure (i.e. inflectional morphology, e.g. the verb ending -s in he paints). Now, in the absence of all semantic cues, including derivational morphology, only BA 44 was active. Additional analyses showed a selective responsiveness of this area to syntax-relevant cues. These findings confirm BA 44 as a core area for the processing of pure syntactic information. This furthermore suggests that the brain represents structural and meaningful aspects of language separately.

Aura status: a not so frequent aura.

BACKGROUND: Migraine aura status is a variety of migraine aura with unvalidated research criteria. AIM AND METHODS: We conducted a systematic review of published cases and a retrospective analysis of 500 cases of migraine with aura to evaluate the applicability and clinical features of ICHD-III beta criteria, compared to a more liberal definition for its diagnosis: ≥3 aura episodes for up to three consecutive days. RESULTS: Many publications under this title correspond to persistent or formerly designated prolonged auras. Nine cases fulfilled ICHD-III beta status criteria. In our series, either 1.7% or 4.2% cases fulfilled ICDH-III beta or our definition, respectively. Regardless of the criteria, aura status patients were older at onset of status than those with typical aura, had a predominance of visual symptoms, normal neuroimaging and no sequelae. Status recurred in a few. CONCLUSION: Both criteria identify a similar population in terms of age, gender, main symptoms, imaging and outcome. Since patients with closely recurring auras might raise the same approach independently of the criteria, the use of more liberal criteria will allow more cases for detailed diagnosis and therapeutic analysis, eventually leading to the identification of subtypes.

Late onset and early onset aura: the same disorder.

Late onset aura (LOA) is usually considered benign but raises diagnostic uncertainties. We compared individuals with LOA (>45 years of age at aura onset) with those of early onset (EOA) in clinical features, vascular risk factors and imaging, in a retrospective study design including patients with migraine aura and age >44 years at first visit. In 77 cases (51 EOA and 26 LOA), no differences were found in gender distribution, family or personal history of migraine without aura, type of aura symptoms or imaging findings. LOA patients' were more likely to not fulfil all ICHD-II aura criteria and to lack headache. This data suggest that LOA and EOA are overall identical but there are differences in presentation that deserve a better characterization by a prospective study.