Neurobiology of Language最新文献

Previous research has shown that word-finding difficulties in older age are associated with functional and structural brain changes. Functional brain networks, measured through electroencephalography, reflect the brain's neurophysiological organisation. However, the utility of functional brain networks, to predict word-finding in older and younger adults has not yet been investigated. This study utilised eyes-closed resting-state electroencephalography data (61 channels) from the Leipzig Study for Mind-Body-Emotion Interactions dataset (Babayan et al., 2019) to investigate the relationship between functional brain networks and word-finding ability in 53 healthy right-handed younger (aged 20-35) and 53 (aged 59-77) older adults. Brain segregation reflects the efficiency of localised brain regions to process information, while brain integration reflects the efficiency of global information processing between distant brain regions. Word-finding ability was quantified as the number of orally produced words during a semantic and letter fluency task. Multiple linear regression revealed that, in older adults, greater synchronised brain activity was associated with lower semantic fluency. Irrespective of age, greater brain segregation was related to lower semantic fluency. Increased brain integration corresponded to greater semantic fluency in older adults. Both older and younger participants with a more optimised balance between brain segregation and integration performed better on semantic fluency. These findings suggest that word-finding ability seems to be related to brain segregation and integration, possibly indicating alterations in cognitive control or compensatory changes in brain activity. The article further provides a discussion on neural dedifferentiation, hyper-synchronisation, study limitations, and directions for future research.

Interlocutors often use the semantics of comprehended speech to inform the semantics of planned speech. Do representations of the comprehension and planning stimuli interact? In this EEG study, we used rapid invisible frequency tagging (RIFT) to better understand the attentional distribution to representations of comprehension and speech planning stimuli, and how they interact in the neural signal. To do this, we leveraged the picture-word interference (PWI) paradigm with delayed naming, where participants simultaneously comprehend auditory distractors (auditory [f1]; tagged at 54 Hz) while preparing to name related or unrelated target pictures (visual [f2]; tagged at 68 Hz). RIFT elicits steady-state evoked potentials, which reflect allocation of attention to the tagged stimuli. When representations of the tagged stimuli interact, increased power has been observed at the intermodulation frequency resulting from an interaction of the base frequencies (f2 ± f1; Drijvers et al., 2021). Our results showed clear power increases at 54 Hz and 68 Hz during the tagging window, but no power difference between the related and unrelated condition. Interestingly, we observed a larger power difference in the intermodulation frequency (compared to baseline) in the unrelated compared to the related condition (68 Hz - 54 Hz: 14 Hz), indicating stronger interaction between unrelated auditory and visual representations. Our results go beyond standard PWI results by showing that participants' difficulties in the related condition do not arise from allocating attention to the pictures or distractors. Instead, processing difficulties arise during interaction of the concepts or lemmas invoked by the two stimuli, thus, we conclude, that interaction might be downregulated in the related condition.

This study investigated whether language serves as the primary organizational axis dividing lexico-semantic representations in multilingual individuals, or whether language is a subsidiary feature to dominant organizing principles identified in monolingual individuals. To address this question, we examined the influence of two well-established principles of language organization-frequency and concreteness-on naming accuracy in a post-stroke bilingual individual with anomic aphasia (PWA). The participant, a highly proficient Basque-Spanish bilingual, underwent MRI scanning to delineate the extent and location of the lesion and completed a naming-by-definition task in both languages, along with a control group of 24 age-matched bilinguals. Stimuli were orthogonally varied by frequency (high/low) and concreteness (high/low). Generalized linear mixed models revealed main effects of both frequency and concreteness on naming accuracy. Notably, while healthy controls showed a robust concreteness effect-with concrete words yielding higher accuracy-the PWA exhibited a disproportionately larger impairment for low-frequency words. This pattern, consistent with the lesion's location to the inferior temporal gyrus, highlights a specific vulnerability of frequency-based lexical representations following temporal lobe damage. Importantly, the bilingual PWA demonstrated strikingly similar error rates across languages, yet an item-level analysis revealed that the specific words affected differed between the two languages. These findings (i) clarify the role of the inferior temporal gyrus in lexical organization, (ii) suggest that bilinguals possess an integrated lexical system governed by general cognitive principles, and (iii) challenge the notion that language itself is the dominant axis of organization in the bilingual mind/brain.

Resting-state functional magnetic resonance imaging (rs-fMRI) enables the evaluation of the language network and is particularly useful for measuring language lateralization with minimal participant effort and methodological biases (e.g., no language task execution or selection). Tractography using diffusion MRI (dMRI) provides complementary information on language-associated white matter bundles. Some structural white matter measures of the left or right hemisphere have been related to the functional language lateralization index (LI) and allow a better understanding of this network. This study utilizes tractography to identify white matter structural predictors of LI from a single hemisphere, employing linear regression and random forest models. Rs-fMRI and dMRI data from 618 healthy subjects of the Human Connectome Project were used to link LI to micro- and macro-structural measures of the arcuate fasciculi, the inferior longitudinal fasciculi, the frontal aslant tracts and sections of the corpus callosum. Results suggest a possible relationship between micro- and macro-structural measures of white matter tracts, and functional language lateralization measured in resting-state. However, the identified predictors are not sufficiently representative to be considered proxies for functional language lateralization. In conclusion, both micro- and macro-structural white matter characteristics as well as both left and right hemispheres are important to consider, but are not sufficient on their own, when investigating the relationship between brain structures and functional language lateralization.

Speech perception can decline in middle age even when hearing thresholds remain normal, and the underlying neurobiological mechanisms are not well understood. In line with the age-related neural dedifferentiation hypothesis, we predicted that middle-aged adults show less distinct cortical representations of phonemes and acoustic-phonetic features relative to younger adults. In addition to an extensive audiological, auditory electrophysiological, and speech perceptual test battery, we measured electroencephalographic responses time-locked to phoneme instances (phoneme-related potential) in naturalistic, continuous speech and trained neural network classifiers to predict phonemes from these responses. Consistent with age-related neural dedifferentiation, phoneme predictions were less accurate, more uncertain, and involved a broader network for middle-aged adults compared with younger adults. Representational similarity analysis revealed that the featural relationship between phonemes was less robust in middle age. Electrophysiological and behavioral measures revealed signatures of putative cochlear neural degeneration (CND) and speech perceptual deficits in middle-aged adults relative to younger adults. In line with prior work in animal models, proxies of CND were associated with greater cortical dedifferentiation, explaining nearly a third of the variance in PRP prediction accuracy together with measures of acoustic neural processing. Notably, even after controlling for CND proxies and acoustic processing abilities, age-group differences in cortical PRP prediction accuracy remained. Overall, the results reveal "fuzzier" cortical phonemic representations in middle age, suggesting that age-related neural dedifferentiation may underlie speech perceptual challenges despite a normal audiogram.

To investigate speech in the developing brain, 94 children aged 4 to 7 years old were scanned using diffusion weighted imaging (DWI) magnetic resonance imaging. To increase sample size and performance variability, we included children with ADHD from a larger ongoing study (n = 47). Each child completed the Syllable Repetition Task (SRT), a validated measure of phoneme articulation. DWI data were modeled using restriction spectrum imaging to measure restricted and hindered diffusion properties in gray and white matter. We analyzed the diffusion data using whole brain analysis and automated fiber quantification (AFQ) analysis to establish tract profiles for the six fiber pathways thought to be important for supporting speech development. In the whole brain analysis, we found that SRT performance was associated with restricted diffusion in left and right inferior frontal gyrus, left and right pars opercularis, right pre-supplementary and supplementary motor area, and left and right cerebellar gray matter (p < 0.005). Age moderated these associations in left pars opercularis and the frontal aslant tract (FAT), but only the cerebellar findings survived a cluster correction. Analyses using AFQ highlighted differences in high and low performing children along specific tract profiles, most notably in left but not right FAT, in left and right superior longitudinal fasciculus III, and in the cerebellar peduncles. These findings suggest that individual differences in speech performance are reflected in structural gray and white matter differences as measured by restricted and hindered diffusion metrics, and offer important insights into developing brain networks supporting speech in very young children.

The left dorsomedial prefrontal cortex (dmPFC) is known to be associated with volition and motor function but is often overlooked in models of the neural bases of language. In this retrospective study, we reveal a robust statistical association between a rare language profile disproportionately affecting self-generated, but not externally cued, language production and damage to left dmPFC in a large (n = 307) neurosurgical database using both voxel-based and multivariate lesion-symptom mapping (VLSM, MLSM). This profile was not attributable to motivational or motor speech deficits. We further demonstrate that the probability of presenting with this profile is nearly 15 times higher following a resection in the dorsomedial prefrontal cortex than a resection elsewhere in the brain. Finally, we present a first person account of recovery from this language syndrome by a professionally trained linguist in the Supplementary Materials. These findings leverage a large dataset to add to the predominantly case-dominated literature demonstrating that damage specific to the dmPFC can cause a unique linguistic disturbance disproportionately affecting spontaneous speech, and provide a rare person-centered narrative of the experience of aphasia that is informative to scientists and clinicians alike. Overall, this work highlights the role of the left dmPFC, rarely included in dominant models of the neural bases of language, in the volitional control of fluent, self-generated speech.

Atypical language lateralization is associated with a different organization of the entire brain. However, it remains unknown whether this cerebral organization is linked to differences in cognitive task performance. In this study, several neuropsychological tests requiring fast processing speed were administered to left-handed participants, classified based on their language lateralization: left language dominance (n = 48), bilateral (n = 15), and right language dominance (n = 23). A factor analysis was conducted to derive three cognitive function dimensions: reading, articulation, and verbal reasoning; spatial processing; and interference/inhibition. The results showed that right language dominance was associated with poorer overall performance, particularly on tasks related to spatial processing, reading, articulation, and verbal reasoning. We conclude that the atypical development of language lateralization is accompanied by lower cognitive skills in tasks requiring speed of processing and interhemispheric connectivity.

This integrative perspective article delves into the crucial role of the superior temporal sulcus (STS) and adjacent perisylvian regions in multimodal integration and semantic cognition. Drawing from a wide range of neuroscientific evidence, including studies on nonhuman primates and human brain evolution, the article highlights the significance of the STS in linking auditory and visual modalities, particularly in the establishment of associative links between auditory inputs and visual stimuli. Furthermore, it explores the expansion of the human temporal lobe and its implications for the amplification of multisensory regions, emphasizing the role of these regions in the development of word-related concepts and semantic networks. We propose a posteroanterior gradient organization in the human temporal lobe, from low-level sensorimotor integration in posterior regions to higher-order, transmodal semantic control in anterior portions, particularly in the anterior temporal lobe. Overall, this perspective provides a comprehensive overview of the functional and evolutionary aspects of the STS and adjacent regions in multimodal integration and semantic cognition, offering valuable insights for future research in this field.

Prenatal alcohol exposure (PAE) is associated with various neurological, behavioral and cognitive deficits, including reading and language. Previous studies have demonstrated altered white matter in children and adolescents with PAE and associations with reading and language performance in children aged 3 years and older. However, little research has focused on the toddler years, despite this being a critical period for behavioral and neural development. We aimed to determine associations between structural brain connectivity and early language skills in toddlers, in the context of PAE. Eighty-eight toddlers (2-3 yr, 56 males), 23 of whom had PAE, underwent a diffusion MRI scan in Cape Town, South Africa, with language skills assessed using the Expressive and Receptive Communication subtests from the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III). Diffusion scans were preprocessed to create a structural network of regions associated with language skills using graph theory analysis. Linear regression models were used to examine moderation effects of PAE on structural network properties and language skills. Toddlers with PAE had higher structural connectivity in language networks than unexposed children. PAE moderated the relationship between structural network properties and Expressive Communication scores. None of the effects survived correction for multiple comparisons. Our findings show weak moderation effects of PAE on structural language network properties and language skills. Our study sheds light on the structural connectivity correlates of early language skills in an understudied population during a critical neurodevelopmental period, laying the foundation for future research.