Vocabulary growth rate from preschool to school-age years is reflected in the connectivity of the arcuate fasciculus in 14-year-old children

Adaptive compensation of arcuate fasciculus lateralization in developmental dyslexia

Previous studies have reported anomalies in the arcuate fasciculus (AF) lateralization in developmental dyslexia (DD). Still, the relationship between AF lateralization and literacy skills in DD remains largely unknown. The purpose of our study is to investigate the relationship between lateralization of three segments of AF (AF anterior segment (AFAS), AF long segment (AFLS), and AF posterior segment (AFPS)) and literacy skills in DD. A total of 26 children with dyslexia and 31 age-matched control children were included in this study. High angular diffusion imaging, combined with spherical deconvolution tractography, was used to reconstruct the AF. Connectivity measures of hindrance-modulated orientational anisotropy (HMOA) were computed for each of the three segments of the AF. The lateralization index (LI) of each AF segment was calculated by (right HMOA - left HMOA)/(right HMOA + left HMOA). Results showed that the LIs of AFAS and AFLS were positively correlated with reading accuracy in children with dyslexia. Specifically, the LI of AFAS was positively correlated with nonword and meaningless text reading accuracy, while the LI of AFLS accounted for word reading accuracy. The results suggest adaptive compensation of arcuate fasciculus lateralization in developmental dyslexia and functional dissociation of the anterior segment and long segment in the compensation.

A narrative review of the anatomy and function of the white matter tracts in language production and comprehension

Much is known about the role of cortical areas in language processing. The shift towards network approaches in recent years has highlighted the importance of uncovering the role of white matter in connecting these areas. However, despite a large body of research, many of these tracts’ functions are not well-understood. We present a comprehensive review of the empirical evidence on the role of eight major tracts that are hypothesized to be involved in language processing (inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, extreme capsule, middle longitudinal fasciculus, superior longitudinal fasciculus, arcuate fasciculus, and frontal aslant tract). For each tract, we hypothesize its role based on the function of the cortical regions it connects. We then evaluate these hypotheses with data from three sources: studies in neurotypical individuals, neuropsychological data, and intraoperative stimulation studies. Finally, we summarize the conclusions supported by the data and highlight the areas needing further investigation.

Do naps benefit novel word learning? Developmental differences and white matter correlates

Memory representations of newly learned words undergo changes during nocturnal sleep, as evidenced by improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning (at least under the present conditions), and emphasize the need to better understand both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.

Encouraging pointing with the right hand, but not the left hand, gives right-handed 3-year-olds a linguistic advantage

Previous research has shown a strong positive association between right-handed gesturing and vocabulary development. However, the causal nature of this relationship remains unclear. In the current study, we tested whether gesturing with the right hand enhances linguistic processing in the left hemisphere, which is contralateral to the right hand. We manipulated the gesture hand children used in pointing tasks to test whether it would affect their performance. In either a linguistic task (verb learning) or a non-linguistic control task (memory), 131 typically developing right-handed 3-year-olds were encouraged to use either their right hand or left hand to respond. While encouraging children to use a specific hand to indicate their responses had no effect on memory performance, encouraging children to use the right hand to respond, compared to the left hand, significantly improved their verb learning performance. This study is the first to show that manipulating the hand with which children are encouraged to gesture gives them a linguistic advantage. Language lateralization in healthy right-handed children typically involves a dominant left hemisphere. Producing right-handed gestures may therefore lead to increased activation in the left hemisphere which may, in turn, facilitate forming and accessing lexical representations. It is important to note that this study manipulated gesture handedness among right-handers and does therefore not support the practice of encouraging children to become right-handed in manual activities. RESEARCH HIGHLIGHTS: Right-handed 3-year-olds were instructed to point to indicate their answers exclusively with their right or left hand in either a memory or verb learning task. Right-handed pointing was associated with improved verb generalization performance, but not improved memory performance. Thus, gesturing with the right hand, compared to the left hand, gives right-handed 3-year-olds an advantage in a linguistic but not a non-linguistic task. Right-handed pointing might lead to increased activation in the left hemisphere and facilitate forming and accessing lexical representations.

The Brain Connectome for Chinese Reading

Chinese, as a logographic language, fundamentally differs from alphabetic languages like English. Previous neuroimaging studies have mainly focused on alphabetic languages, while the exploration of Chinese reading is still an emerging and fast-growing research field. Recently, a growing number of neuroimaging studies have explored the neural circuit of Chinese reading. Here, we summarize previous research on Chinese reading from a connectomic perspective. Converging evidence indicates that the left middle frontal gyrus is a specialized hub region that connects the ventral with dorsal pathways for Chinese reading. Notably, the orthography-to-phonology and orthography-to-semantics mapping, mainly processed in the ventral pathway, are more specific during Chinese reading. Besides, in addition to the left-lateralized language-related regions, reading pathways in the right hemisphere also play an important role in Chinese reading. Throughout, we comprehensively review prior findings and emphasize several challenging issues to be explored in future work.

Mechanical Properties of the Developing Brain are Associated with Language Input and Vocabulary Outcome

The quality of language that children hear in their environment is associated with the development of language-related brain regions, in turn promoting vocabulary knowledge. Although informative, it remains unknown how these environmental influences alter the structure of neural tissue and subsequent vocabulary outcomes. The current study uses magnetic resonance elastography (MRE) to examine how children's language environments underlie brain tissue mechanical properties, characterized as brain tissue stiffness and damping ratio, and promote vocabulary knowledge. Twenty-five children, ages 5-7, had their audio and video recorded while engaging in a play session with their parents. Children also completed the Picture Vocabulary Task (from NIH Toolbox) and participated in an MRI, where MRE and anatomical images were acquired. Higher quality input was associated with greater stiffness in the bilateral inferior frontal gyrus and right superior temporal gyrus, whereas greater vocabulary knowledge was associated with lower damping ratio in the right inferior frontal gyrus. These findings suggest changes in neural tissue composition are sensitive to malleable aspects of the environment, whereas tissue organization is more strongly associated with vocabulary outcome. Notably, these associations were independent of maternal education, suggesting more proximal measures of a child's environment may be the source of differences in neural tissue structure underlying variability in vocabulary outcomes.

Left and Right Arcuate Fasciculi Are Uniquely Related to Word Reading Skills in Chinese-English Bilingual Children

Whether reading in different writing systems recruits language-unique or language-universal neural processes is a long-standing debate. Many studies have shown the left arcuate fasciculus (AF) to be involved in phonological and reading processes. In contrast, little is known about the role of the right AF in reading, but some have suggested that it may play a role in visual spatial aspects of reading or the prosodic components of language. The right AF may be more important for reading in Chinese due to its logographic and tonal properties, but this hypothesis has yet to be tested. We recruited a group of Chinese-English bilingual children (8.2 to 12.0 years old) to explore the common and unique relation of reading skill in English and Chinese to fractional anisotropy (FA) in the bilateral AF. We found that both English and Chinese reading skills were positively correlated with FA in the rostral part of the left AF-direct segment. Additionally, English reading skill was positively correlated with FA in the caudal part of the left AF-direct segment, which was also positively correlated with phonological awareness. In contrast, Chinese reading skill was positively correlated with FA in certain segments of the right AF, which was positively correlated with visual spatial ability, but not tone discrimination ability. Our results suggest that there are language universal substrates of reading across languages, but that certain left AF nodes support phonological mechanisms important for reading in English, whereas certain right AF nodes support visual spatial mechanisms important for reading in Chinese.

White matter in infancy is prospectively associated with language outcomes in kindergarten

Language acquisition is of central importance to child development. Although this developmental trajectory is shaped by experience postnatally, the neural basis for language emerges prenatally. Thus, a fundamental question remains: do structural foundations for language in infancy predict long-term language abilities? Longitudinal investigation of 40 children from infancy to kindergarten reveals that white matter in infancy is prospectively associated with subsequent language abilities, specifically between: (i) left arcuate fasciculus and phonological awareness and vocabulary knowledge, (ii) left corticospinal tract and phonological awareness, and bilateral corticospinal tract with phonological memory; controlling for age, cognitive, and environmental factors. Findings link white matter in infancy with school-age language abilities, suggesting that white matter organization in infancy sets a foundation for long-term language development.

The development of brain rhythms at rest and its impact on vocabulary acquisition

A long-standing question in developmental science is how the neurodevelopment of the brain influences cognitive functions. Here, we examined the developmental change of resting EEG power and its links to vocabulary acquisition in school-age children. We further explored what mechanisms may mediate the relation between brain rhythm maturation and vocabulary knowledge. Eyes-opened resting-state EEG data were recorded from 53 typically-developing Chinese children every 2 years between the ages of 7 and 11. Our results showed first that delta, theta, and gamma power decreased over time, whereas alpha and beta power increased over time. Second, after controlling for general cognitive abilities, age, home literacy environment, and phonological skills, theta decreases explained 6.9% and 14.4% of unique variance in expressive vocabulary at ages 9 and 11, respectively. We also found that beta increase from age 7 to 9 significantly predicted receptive vocabulary at age 11. Finally, theta decrease predicted expressive vocabulary through the effects of phoneme deletion at age 9 and tone discrimination at age 11. These results substantiate the important role of brain oscillations at rest, especially theta rhythm, in language development. The developmental change of brain rhythms could serve as sensitive biomarkers for vocabulary development in school-age children, which would be of great value in identifying children at risk of language impairment.

Negative polarity in quantifiers evokes greater activation in language-related regions compared to negative polarity in adjectives

The processing of sentences with negative quantifiers (e.g., few) is more costly than of sentences that contain their positive counterparts (e.g., many). While this polarity effect is robust and reliably replicable, its neurological bases are not well understood. In this study, we use functional magnetic resonance imaging (fMRI) paradigm for 30 participants to assess the polarity effect in sentences with polar quantifiers, and compare it with the polarity effect of polar adjectives. Both in quantifiers and in adjectives, the polarity effect manifests in the anterior insula bilaterally. The polarity effect in quantifiers, however, shows greater activation in the left hemisphere than it does for adjectives. In particular, left inferior frontal gyrus (IFG) and left superior temporal sulcus (STS) show increased activation for polarity in quantifiers than in adjectives, which is the evidence for the specific involvement of the language network in this type of polarity processing. Using the polarity effect in adjectives as a control, we provide further evidence for the linguistic complexity that negative quantifiers implicate on processing.

Effects of socioeconomic status in predicting reading outcomes for children: The mediation of spoken language network

The present longitudinal study investigated the effects of early childhood socioeconomic status on language-related resting-state functional connectivity and reading outcome in adolescence. Seventy-nine children participated in this study. Socioeconomic status was measured via parent questionnaire measuring parental education and family income at 1 month. At age 14, resting-state fMRI data and reading-related behavioral data of the children were collected. Resting-state functional connectivity (RSFC) analysis was performed based on four regions of interest, including the left inferior frontal gyrus (L.IFG), left anterior superior temporal gyrus (L.aSTG), left posterior superior temporal gyrus (L.pSTG) and right anterior superior temporal gyrus (R.aSTG). Significant associations were found between parental education and the language-related RSFC, including the RSFC of L.IFG-L.aSTG and the RSFC of L.aSTG-L.pSTG, while no association was found between family income and language-related RSFC. Furthermore, the parental education-associated functional connectivity patterns (i.e., L.IFG-L.aSTG and L.aSTG-L.pSTG) were found to be positively correlated with children's reading skills (word list reading and sentence reading fluency). Finally, path analyses indicated that the intrinsic brain connectivity between L.aSTG and L.pSTG influenced the relationship between parental education and children's reading outcomes.

Age of Speech Onset in Autism Relates to Structural Connectivity in the Language Network

Speech onset delays (SOD) and language atypicalities are central aspects of the autism spectrum (AS), despite not being included in the categorical diagnosis of AS. Previous studies separating participants according to speech onset history have shown distinct patterns of brain organization and activation in perceptual tasks. One major white matter tract, the arcuate fasciculus (AF), connects the posterior temporal and left frontal language regions. Here, we used anatomical brain imaging to investigate the properties of the AF in adolescent and adult autistic individuals with typical levels of intelligence who differed by age of speech onset. The left AF of the AS group showed a significantly smaller volume than that of the nonautistic group. Such a reduction in volume was only present in the younger group. This result was driven by the autistic group without SOD (SOD−), despite their typical age of speech onset. The autistic group with SOD (SOD+) showed a more typical AF as adults relative to matched controls. This suggests that, along with multiple studies in AS-SOD+ individuals, atypical brain reorganization is observable in the 2 major AS subgroups and that such reorganization applies mostly to the language regions in SOD− and perceptual regions in SOD+ individuals.

Influences of the early family environment and long-term vocabulary development on the structure of white matter pathways: A longitudinal investigation

In the present longitudinal study, we investigated the joint effect of early family factors and long-term vocabulary development on the structure of reading-related white matter pathways in adolescents. Seventy-nine children participated in this study. Family environment was measured via parental questionnaire between age 1 and age 3. From age 4 to age 10, children's vocabulary skills were tested annually. At age 14, diffusion tensor imaging data of the children were collected. Using individual-based tractography, 10 reading-related tracts of the two hemispheres were delineated. Different family factors were found to be correlated with different pathways: Age of literacy exposure was correlated with fractional anisotropy of the direct segment of the left arcuate fasciculus, while an association trend was found between early family socioeconomic status and fractional anisotropy of the left inferior frontal occipital fasciculus. Further regression analyses showed that the age of literacy exposure modulated the relationships between vocabulary development and the structure of the left arcuate fasciculus. Specifically, in the earlier literacy exposure group, no association was found between vocabulary development and the strength of the arcuate fasciculus, whereas in the later literacy exposure group, significant associations were found between vocabulary development and the strength of the arcuate fasciculus.

Language development and brain reorganization in a child born without the left hemisphere

We present a case of a 14-year-old girl born without the left hemisphere due to prenatal left internal carotid occlusion. We combined longitudinal language and cognitive assessments with functional and structural neuroimaging data to situate the case within age-matched, typically developing children. Despite having had a delay in getting language off the ground during the preschool years, our case performed within the normal range on a variety of standardized language tests, and exceptionally well on phonology and word reading, during the elementary and middle school years. Moreover, her spatial, number, and reasoning skills also fell in the average to above-average range based on assessments during these time periods. Functional MRI data revealed activation in right fronto-temporal areas when listening to short stories, resembling the bilateral activation patterns in age-matched typically developing children. Diffusion MRI data showed significantly larger dorsal white matter association tracts (the direct and anterior segments of the arcuate fasciculus) connecting areas active during language processing in her remaining right hemisphere, compared to either hemisphere in control children. We hypothesize that these changes in functional and structural brain organization are the result of compensatory brain plasticity, manifesting in unusually large right dorsal tracts, and exceptional performance in phonology, speech repetition, and decoding. More specifically, we posit that our case's large white matter connections might have played a compensatory role by providing fast and reliable transfer of information between cortical areas for language in the right hemisphere.

Cognitive and neural mechanisms underlying the mnemonic effect of songs after stroke

Sung melody provides a mnemonic cue that can enhance the acquisition of novel verbal material in healthy subjects. Recent evidence suggests that also stroke patients, especially those with mild aphasia, can learn and recall novel narrative stories better when they are presented in sung than spoken format. Extending this finding, the present study explored the cognitive mechanisms underlying this effect by determining whether learning and recall of novel sung vs. spoken stories show a differential pattern of serial position effects (SPEs) and chunking effects in non-aphasic and aphasic stroke patients (N = 31) studied 6 months post-stroke. The structural neural correlates of these effects were also explored using voxel-based morphometry (VBM) and deterministic tractography (DT) analyses of structural MRI data. Non-aphasic patients showed more stable recall with reduced SPEs in the sung than spoken task, which was coupled with greater volume and integrity (indicated by fractional anisotropy, FA) of the left arcuate fasciculus. In contrast, compared to non-aphasic patients, the aphasic patients showed a larger recency effect (better recall of the last vs. middle part of the story) and enhanced chunking (larger units of correctly recalled consecutive items) in the sung than spoken task. In aphasics, the enhanced chunking and better recall on the middle verse in the sung vs. spoken task correlated also with better ability to perceive emotional prosody in speech. Neurally, the sung > spoken recency effect in aphasic patients was coupled with greater grey matter volume in a bilateral network of temporal, frontal, and parietal regions and also greater volume of the right inferior fronto-occipital fasciculus (IFOF). These results provide novel cognitive and neurobiological insight on how a repetitive sung melody can function as a verbal mnemonic aid after stroke.

•

Non-aphasic stroke patients show more stable recall of sung than spoken stories.

•

Aphasic patients show larger recency and chunking effects to sung vs. spoken stories.

•

The left dorsal pathway mediates better recall of sung stories in non-aphasics.

•

The right ventral pathway mediates better recall of sung stories in aphasics.

•

Large-scale bilateral cortical networks are linked to musical mnemonics in aphasia.

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.

Language Exposure Relates to Structural Neural Connectivity in Childhood

Neuroscience research has elucidated broad relationships between socioeconomic status (SES) and young children's brain structure, but there is little mechanistic knowledge about specific environmental factors that are associated with specific variation in brain structure. One environmental factor, early language exposure, predicts children's linguistic and cognitive skills and later academic achievement, but how language exposure relates to neuroanatomy is unknown. By measuring the real-world language exposure of young children (ages 4-6 years, 27 male/13 female), we confirmed the preregistered hypothesis that greater adult-child conversational experience, independent of SES and the sheer amount of adult speech, is related to stronger, more coherent white matter connectivity in the left arcuate and superior longitudinal fasciculi on average, and specifically near their anterior termination at Broca's area in left inferior frontal cortex. Fractional anisotropy of significant tract subregions mediated the relationship between conversational turns and children's language skills and indicated a neuroanatomical mechanism underlying the SES "language gap." Post hoc whole-brain analyses revealed that language exposure was not related to any other white matter tracts, indicating the specificity of this relationship. Results suggest that the development of dorsal language tracts is environmentally influenced, specifically by early, dialogic interaction. Furthermore, these findings raise the possibility that early intervention programs aiming to ameliorate disadvantages in development due to family SES may focus on increasing children's conversational exposure to capitalize on the early neural plasticity underlying cognitive development.SIGNIFICANCE STATEMENT Over the last decade, cognitive neuroscience has highlighted the detrimental impact of disadvantaged backgrounds on young children's brain structure. However, to intervene effectively, we must know which proximal aspects of the environmental aspects are most strongly related to neural development. The present study finds that young children's real-world language exposure, and specifically the amount of adult-child conversation, correlates with the strength of connectivity in the left hemisphere white matter pathway connecting two canonical language regions, independent of socioeconomic status and the sheer volume of adult speech. These findings suggest that early intervention programs aiming to close the achievement gap may focus on increasing children's conversational exposure to capitalize on the early neural plasticity underlying cognitive development.