Multimodal imaging of brain reorganization in hearing late learners of sign language

Early language experience and modality affect parietal cortex activation in different hemispheres: Insights from hearing bimodal bilinguals

The goal of this study was to investigate the impact of the age of acquisition (AoA) on functional brain representations of sign language in two exceptional groups of hearing bimodal bilinguals: native signers (simultaneous bilinguals since early childhood) and late signers (proficient sequential bilinguals, who learnt a sign language after puberty). We asked whether effects of AoA would be present across languages - signed and audiovisual spoken - and thus observed only in late signers as they acquired each language at different life stages, and whether effects of AoA would be present during sign language processing across groups. Moreover, we aimed to carefully control participants' level of sign language proficiency by implementing a battery of language tests developed for the purpose of the project, which confirmed that participants had high competences of sign language. Between-group analyses revealed a hypothesized modulatory effect of AoA in the right inferior parietal lobule (IPL) in native signers, compared to late signers. With respect to within-group differences across languages we observed greater involvement of the left IPL in response to sign language in comparison to spoken language in both native and late signers, indicating language modality effects. Overall, our results suggest that the neural underpinnings of language are molded by the linguistic characteristics of the language as well as by when in life the language is learnt.

Neural underpinnings of sentence reading in deaf, native sign language users

The goal of this study was to investigate sentence-level reading circuits in deaf native signers, a unique group of deaf people who are immersed in a fully accessible linguistic environment from birth, and hearing readers. Task-based fMRI, functional connectivity and lateralization analyses were conducted. Both groups exhibited overlapping brain activity in the left-hemispheric perisylvian regions in response to a semantic sentence task. We found increased activity in left occipitotemporal and right frontal and temporal regions in deaf readers. Lateralization analyses did not confirm more rightward asymmetry in deaf individuals. Deaf readers exhibited weaker functional connectivity between inferior frontal and middle temporal gyri and enhanced coupling between temporal and insular cortex. In conclusion, despite the shared functional activity within the semantic reading network across both groups, our results suggest greater reliance on cognitive control processes for deaf readers, possibly resulting in greater effort required to perform the task in this group.

Understanding functional brain reorganization for naturalistic piano playing in novice pianists

Learning to play the piano is a unique complex task, integrating multiple sensory modalities and higher order cognitive functions. Longitudinal neuroimaging studies on adult novice musicians show training-related functional changes in music perception tasks. The reorganization of brain activity while actually playing an instrument was studied only on a very short time frame of a single fMRI session, and longer interventions have not yet been performed. Thus, our aim was to investigate the dynamic complexity of functional brain reorganization while playing the piano within the first half year of musical training. We scanned 24 novice keyboard learners (female, 18-23 years old) using fMRI while they played increasingly complex musical pieces after 1, 6, 13, and 26 weeks of training. Playing music evoked responses bilaterally in the auditory, inferior frontal, and supplementary motor areas, and the left sensorimotor cortex. The effect of training over time, however, invoked widespread changes encompassing the right sensorimotor cortex, cerebellum, superior parietal cortex, anterior insula and hippocampus, among others. As the training progressed, the activation of these regions decreased while playing music. Post hoc analysis revealed region-specific time-courses for independent auditory and motor regions of interest. These results suggest that while the primary sensory, motor, and frontal regions are associated with playing music, the training decreases the involvement of higher order cognitive control and integrative regions, and basal ganglia. Moreover, training might affect distinct brain regions in different ways, providing evidence in favor of the dynamic nature of brain plasticity.

Increased functional connectivity between the auditory cortex and the frontoparietal network compensates for impaired visuomotor transformation after early auditory deprivation

Early auditory deprivation leads to a reorganization of large-scale brain networks involving and extending beyond the auditory system. It has been documented that visuomotor transformation is impaired after early deafness, associated with a hyper-crosstalk between the task-critical frontoparietal network and the default-mode network. However, it remains unknown whether and how the reorganized large-scale brain networks involving the auditory cortex contribute to impaired visuomotor transformation after early deafness. Here, we asked deaf and early hard of hearing participants and normal hearing controls to judge the spatial location of a visual target. Compared with normal hearing controls, the superior temporal gyrus showed significantly increased functional connectivity with the frontoparietal network and the default-mode network in deaf and early hard of hearing participants, specifically during egocentric judgments. However, increased superior temporal gyrus-frontoparietal network and superior temporal gyrus-default-mode network coupling showed antagonistic effects on egocentric judgments. In deaf and early hard of hearing participants, increased superior temporal gyrus-frontoparietal network connectivity was associated with improved egocentric judgments, whereas increased superior temporal gyrus-default-mode network connectivity was associated with deteriorated performance in the egocentric task. Therefore, the data suggest that the auditory cortex exhibits compensatory neuroplasticity (i.e. increased functional connectivity with the task-critical frontoparietal network) to mitigate impaired visuomotor transformation after early auditory deprivation.

Word frequency and reading demands modulate brain activation in the inferior frontal gyrus

Processing efficiency differs between high- and low-frequency words, with less frequent words resulting in longer response latencies in several linguistic behavioral tasks. Nevertheless, studies using functional MRI to investigate the word frequency effect have employed diverse methodologies and produced heterogeneous results. In this study, we examine the effect of word frequency through complementary analytical approaches and functional connectivity analyses. Furthermore, we examine whether reading demands, which have been shown to influence reading-related activation, modulate the effects of word frequency. We conducted MRI scanning on 54 healthy participants who performed two versions of a single-word reading task involving high- and low-frequency words: a low-level perceptual reading task and a high-level semantic reading task. The results indicate that word frequency influenced the activation of the pars orbitalis and pars triangularis of the inferior frontal gyrus, but only in the semantic reading task. Additionally, the ventral occipitotemporal cortex exhibited stronger regional activation during the semantic reading task compared to the perceptual reading task, with no effects of word frequency. Functional connectivity analyses demonstrated significant coupling among regions within both the dorsal and ventral reading networks, without any observable effects of word frequency or task. These findings were consistent across group- and individual-level analytical approaches. Overall, our results provide further support for the involvement of the inferior frontal gyrus in semantic processing during reading, as indicated by the effect of word frequency and the influence of reading demands, highlighting the role of the ventral reading network. These findings are discussed in line with their implications for lexical and pre-lexical reading processing.

Exploring the ventral white matter language network in bimodal and unimodal bilinguals

We used diffusion magnetic resonance imaging tractography to investigate the effect of language modality on the anatomy of the ventral white matter language network by comparing unimodal (Italian/English) and bimodal bilinguals (Italian/Italian Sign Language). We extracted the diffusion tractography measures of the Inferior Longitudinal fasciculus (ILF), Uncinate fasciculus (UF) and Inferior Fronto-Occipital fasciculus (IFOF) and we correlated them with the degree of bilingualism and the individual performance in fluency tasks. For both groups of bilinguals, the microstructural properties of the right ILF were correlated with individual level of proficiency in L2, confirming the involvement of this tract in bilingualism. In addition, we found that the degree of left lateralization of the ILF predicted the performance in semantic fluency in L1. The microstructural properties of the right UF correlated with performance in phonological fluency in L1, only for bimodal bilinguals. Overall, the pattern shows both similarities and differences between the two groups of bilinguals.

Associations Between Sign Language Skills and Resting-State Functional Connectivity in Deaf Early Signers

The processing of a language involves a neural language network including temporal, parietal, and frontal cortical regions. This applies to spoken as well as signed languages. Previous research suggests that spoken language proficiency is associated with resting-state functional connectivity (rsFC) between language regions and other regions of the brain. Given the similarities in neural activation for spoken and signed languages, rsFC-behavior associations should also exist for sign language tasks. In this study, we explored the associations between rsFC and two types of linguistic skills in sign language: phonological processing skill and accuracy in elicited sentence production. Fifteen adult, deaf early signers were enrolled in a resting-state functional magnetic resonance imaging (fMRI) study. In addition to fMRI data, behavioral tests of sign language phonological processing and sentence reproduction were administered. Using seed-to-voxel connectivity analysis, we investigated associations between behavioral proficiency and rsFC from language-relevant nodes: bilateral inferior frontal gyrus (IFG) and posterior superior temporal gyrus (STG). Results showed that worse sentence processing skill was associated with stronger positive rsFC between the left IFG and left sensorimotor regions. Further, sign language phonological processing skill was associated with positive rsFC from right IFG to middle frontal gyrus/frontal pole although this association could possibly be explained by domain-general cognitive functions. Our findings suggest a possible connection between rsFC and developmental language outcomes in deaf individuals.

Sign and Spoken Language Processing Differences in the Brain: A Brief Review of Recent Research

Background:

It is currently accepted that sign languages and spoken languages have significant processing commonalities. The evidence supporting this often merely investigates frontotemporal pathways, perisylvian language areas, hemispheric lateralization, and event-related potentials in typical settings. However, recent evidence has explored beyond this and uncovered numerous modality-dependent processing differences between sign languages and spoken languages by accounting for confounds that previously invalidated processing comparisons and by delving into the specific conditions in which they arise. However, these processing differences are often shallowly dismissed as unspecific to language.

Summary:

This review examined recent neuroscientific evidence for processing differences between sign and spoken language modalities and the arguments against these differences’ importance. Key distinctions exist in the topography of the left anterior negativity (LAN) and with modulations of event-related potential (ERP) components like the N400. There is also differential activation of typical spoken language processing areas, such as the conditional role of the temporal areas in sign language (SL) processing. Importantly, sign language processing uniquely recruits parietal areas for processing phonology and syntax and requires the mapping of spatial information to internal representations. Additionally, modality-specific feedback mechanisms distinctively involve proprioceptive post-output monitoring in sign languages, contrary to spoken languages’ auditory and visual feedback mechanisms. The only study to find ERP differences post-production revealed earlier lexical access in sign than spoken languages. Themes of temporality, the validity of an analogous anatomical mechanisms viewpoint, and the comprehensiveness of current language models were also discussed to suggest improvements for future research.

Key message:

Current neuroscience evidence suggests various ways in which processing differs between sign and spoken language modalities that extend beyond simple differences between languages. Consideration and further exploration of these differences will be integral in developing a more comprehensive view of language in the brain.

Multiple amplified microRNAs monitoring in living cells based on fluorescence quenching of Mo2B and hybridization chain reaction

Imaging intracellular microRNAs (miRNAs) demonstrated an essential role in exposing their biological and pathological functions. However, the detection of sequence-specific miRNAs in living cells remains a key challenge. Herein, a facile amplified multiple intracellular miRNAs imaging platform was constructed based on Mo₂B nanosheets (NSs) fluorescence (FL) quenching and hybridization chain reaction (HCR). The Mo₂B NSs demonstrated strong interaction with the hairpin probes (HPs), ssDNA loop, and excellent multiple FL dyes quenching performance, achieving ultralow background signal. After transfection, the HPs recognized specific targets miRNAs, the corresponding HCR was triggered to produce tremendous DNA-miRNA duplex helixes, which dissociated from the surface of the Mo₂B NSs to produce strong FL for miRNAs detection. It realized to image multiple miRNAs biomarkers in different cells to discriminate cancer cells from normal cells owing to the excellent sensitivity, and the regulated expression change of miRNAs in cancer cells was also successfully monitored. The facile and versatile Mo₂B-based FL quenching platform open an avenue to profile miRNAs expression pattern in living cells, and has great applications in miRNAs based biological and biomedical research.

Temporal Dynamics of Brain White Matter Plasticity in Sighted Subjects during Tactile Braille Learning: A Longitudinal Diffusion Tensor Imaging Study

The white matter (WM) architecture of the human brain changes in response to training, though fine-grained temporal characteristics of training-induced white matter plasticity remain unexplored. We investigated white matter microstructural changes using diffusion tensor imaging at five different time points in 26 sighted female adults during 8 months of training on tactile braille reading. Our results show that training-induced white matter plasticity occurs both within and beyond the trained sensory modality, as reflected by fractional anisotropy (FA) increases in somatosensory and visual cortex, respectively. The observed changes followed distinct time courses, with gradual linear FA increase along the training in the somatosensory cortex and sudden visual cortex cross-modal plasticity occurring after braille input became linguistically meaningful. WM changes observed in these areas returned to baseline after the cessation of learning in line with the supply-demand model of plasticity. These results also indicate that the temporal dynamics of microstructural plasticity in different cortical regions might be modulated by the nature of computational demands. We provide additional evidence that observed FA training-induced changes are behaviorally relevant to tactile reading. Together, these results demonstrate that WM plasticity is a highly dynamic process modulated by the introduction of novel experiences.SIGNIFICANCE STATEMENT Throughout the lifetime the human brain is shaped by various experiences. Training-induced reorganization in white matter (WM) microstructure has been reported, but we know little about its temporal dynamics. To fill this gap, we scanned sighted subjects five times during tactile braille reading training. We observed different dynamics of WM plasticity in the somatosensory and visual cortices implicated in braille reading. The former showed a continuous increase in WM tissue anisotropy along with tactile training, while microstructural changes in the latter were observed only after the participants learned to read braille words. Our results confirm the supply-demand model of brain plasticity and provide evidence that WM reorganization depends on distinct computational demands and functional roles of regions involved in the trained skill.

How Musical Training Shapes the Adult Brain: Predispositions and Neuroplasticity

Learning to play a musical instrument is a complex task that integrates multiple sensory modalities and higher-order cognitive functions. Therefore, musical training is considered a useful framework for the research on training-induced neuroplasticity. However, the classical nature-or-nurture question remains, whether the differences observed between musicians and non-musicians are due to predispositions or result from the training itself. Here we present a review of recent publications with strong focus on experimental designs to better understand both brain reorganization and the neuronal markers of predispositions when learning to play a musical instrument. Cross-sectional studies identified structural and functional differences between the brains of musicians and non-musicians, especially in regions related to motor control and auditory processing. A few longitudinal studies showed functional changes related to training while listening to and producing music, in the motor network and its connectivity with the auditory system, in line with the outcomes of cross-sectional studies. Parallel changes within the motor system and between the motor and auditory systems were revealed for structural connectivity. In addition, potential predictors of musical learning success were found including increased brain activation in the auditory and motor systems during listening, the microstructure of the arcuate fasciculus, and the functional connectivity between the auditory and the motor systems. We show that “the musical brain” is a product of both the natural human neurodiversity and the training practice.