High-Resolution Tractography Protocol to Investigate the Pathways between Human Mediodorsal Thalamic Nucleus and Prefrontal Cortex.

Animal studies have established that the mediodorsal nucleus (MD) of the thalamus is heavily and reciprocally connected with all areas of the prefrontal cortex (PFC). In humans, however, these connections are difficult to investigate. High-resolution imaging protocols capable of reliably tracing the axonal tracts linking the human MD with each of the PFC areas may thus be key to advance our understanding of the variation, development, and plastic changes of these important circuits, in health and disease. Here, we tested in adult female and male humans the reliability of a new reconstruction protocol based on in vivo diffusion MRI to trace, measure, and characterize the fiber tracts interconnecting the MD with 39 human PFC areas per hemisphere. Our protocol comprised the following three components: (1) defining regions of interest; (2) preprocessing diffusion data; and, (3) modeling white matter tracts and tractometry. This analysis revealed largely separate PFC territories of reciprocal MD-PFC tracts bearing striking resemblance with the topographic layout observed in macaque connection-tracing studies. We then examined whether our protocol could reliably reconstruct each of these MD-PFC tracts and their profiles across test and retest sessions. Results revealed that this protocol was able to trace and measure, in both left and right hemispheres, the trajectories of these 39 area-specific axon bundles with good-to-excellent test-retest reproducibility. This protocol, which has been made publicly available, may be relevant for cognitive neuroscience and clinical studies of normal and abnormal PFC function, development, and plasticity.SIGNIFICANCE STATEMENT Reciprocal MD-PFC interactions are critical for complex human cognition and learning. Reliably tracing, measuring and characterizing MD-PFC white matter tracts using high-resolution noninvasive methods is key to assess individual variation of these systems in humans. Here, we propose a high-resolution tractography protocol that reliably reconstructs 39 area-specific MD-PFC white matter tracts per hemisphere and quantifies structural information from diffusion MRI data. This protocol revealed a detailed mapping of thalamocortical and corticothalamic MD-PFC tracts in four different PFC territories (dorsal, medial, orbital/frontal pole, inferior frontal) showing structural connections resembling those observed in tracing studies with macaques. Furthermore, our automated protocol revealed high test-retest reproducibility and is made publicly available, constituting a step forward in mapping human MD-PFC circuits in clinical and academic research.

Verbal production dynamics and plasticity: functional contributions of language and executive control systems.

Bilingual language production requires both language knowledge and language control in order to communicate in a target language. Learning or improving a language in adulthood is an increasingly common undertaking, and this has complex effects on the cognitive and neural processes underlying language production. The current functional magnetic resonance imaging (fMRI) experiment investigated the functional plasticity of verbal production in adult language learners, and examined the dynamics of word retrieval in order to dissociate the contributions of language knowledge and executive control. Thirty four adults who were either intermediate or advanced language learners, underwent MRI scanning while performing verbal fluency tasks in their native and new languages. A multipronged analytical approach revealed (i) time-varying contributions of language knowledge and executive control to verbal fluency performance, (ii) learning-related changes in the functional correlates of verbal fluency in both the native and new languages, (iii) no effect of learning on lateralization, and (iv) greater functional coupling between language and language control regions with greater second language experience. Collectively, our results point to significant functional plasticity in adult language learners that impacts the neural correlates of production in both the native and new languages, and provide new insight into the widely used verbal fluency task.

Functional characterization of correct and incorrect feature integration.

Our sensory system constantly receives information from the environment and our own body. Despite our impression to the contrary, we remain largely unaware of this information and often cannot report it correctly. Although perceptual processing does not require conscious effort on the part of the observer, it is often complex, giving rise to errors such as incorrect integration of features (illusory conjunctions). In the present study, we use functional magnetic resonance imaging to study the neural bases of feature integration in a dual task that produced ~30% illusions. A distributed set of regions demonstrated increased activity for correct compared to incorrect (illusory) feature integration, with increased functional coupling between occipital and parietal regions. In contrast, incorrect feature integration (illusions) was associated with increased occipital (V1-V2) responses at early stages, reduced functional connectivity between right occipital regions and the frontal eye field at later stages, and an overall decrease in coactivation between occipital and parietal regions. These results underscore the role of parietal regions in feature integration and highlight the relevance of functional occipito-frontal interactions in perceptual processing.

Neural basis of social attention: common and distinct mechanisms for social and nonsocial orienting stimuli.

Social and nonsocial directional stimuli (such as gaze and arrows, respectively) share their ability to trigger attentional processes, although the issue of whether social stimuli generate other additional (and unique) attentional effects is still under debate. In this study, we used the spatial interference paradigm to explore, using functional magnetic resonance imaging, shared and dissociable brain activations produced by gaze and arrows. Results showed a common set of regions (right parieto-temporo-occipital) similarly involved in conflict resolution for gaze and arrows stimuli, which showed stronger co-activation for incongruent than congruent trials. The frontal eye field showed stronger functional connectivity with occipital regions for congruent as compared with incongruent trials, and this effect was enhanced for gaze as compared with arrow stimuli in the right hemisphere. Moreover, spatial interference produced by incongruent (as compared with congruent) arrows was associated with increased functional coupling between the right frontal eye field and a set of regions in the left hemisphere. This result was not observed for incongruent (as compared with congruent) gaze stimuli. The right frontal eye field also showed greater coupling with left temporo-occipital regions for those conditions in which larger conflict was observed (arrow incongruent vs. gaze incongruent trials, and gaze congruent vs. arrow congruent trials). These findings support the view that social and nonsocial stimuli share some attentional mechanisms, while at the same time highlighting other differential effects. Highlights Attentional orienting triggered by social (gaze) and nonsocial (arrow) cues is comparable. When social and nonsocial stimuli are used as targets, qualitatively different behavioral effects are observed. This study explores the neural bases of shared and dissociable neural mechanisms for social and nonsocial stimuli. Shared mechanisms were found in the functional coupling between right parieto-temporo-occipital regions. Dissociable mechanisms were found in the functional coupling between right frontal eye field and ipsilateral and contralateral occipito-temporal regions.

Functional underpinnings of feedback-enhanced test-potentiated encoding.

The testing effect describes the finding that retrieval practice enhances memory performance compared to restudy practice. Prior evidence demonstrates that this effect can be boosted by providing feedback after retrieval attempts (i.e. test-potentiated encoding [TPE]). The present fMRI study investigated the neural processes during successful memory retrieval underlying this beneficial effect of correct answer feedback compared with restudy and whether additional performance feedback leads to further benefits. Twenty-seven participants learned cue-target pairs by (i) restudying, (ii) standard TPE including a restudy opportunity, or (iii) TPE including a restudy opportunity immediately after a positive or negative performance feedback. One day later, a cued retrieval recognition test was performed inside the MRI scanner. Behavioral results confirmed the testing effect and that adding explicit performance feedback-enhanced memory relative to restudy and standard TPE. Stronger functional engagement while retrieving items previously restudied was found in lateral prefrontal cortex and superior parietal lobe. By contrast, lateral temporo-parietal areas were more strongly recruited while retrieving items previously tested. Performance feedback increased the hippocampal activation and resulted in stronger functional coupling between hippocampus, supramarginal gyrus, and ventral striatum with lateral temporo-parietal cortex. Our results unveil the main functional dynamics and connectivity nodes underlying memory benefits from additional performance feedback.

Accurate Bayesian segmentation of thalamic nuclei using diffusion MRI and an improved histological atlas.

The human thalamus is a highly connected brain structure, which is key for the control of numerous functions and is involved in several neurological disorders. Recently, neuroimaging studies have increasingly focused on the volume and connectivity of the specific nuclei comprising this structure, rather than looking at the thalamus as a whole. However, accurate identification of cytoarchitectonically designed histological nuclei on standard in vivo structural MRI is hampered by the lack of image contrast that can be used to distinguish nuclei from each other and from surrounding white matter tracts. While diffusion MRI may offer such contrast, it has lower resolution and lacks some boundaries visible in structural imaging. In this work, we present a Bayesian segmentation algorithm for the thalamus. This algorithm combines prior information from a probabilistic atlas with likelihood models for both structural and diffusion MRI, allowing segmentation of 25 thalamic labels per hemisphere informed by both modalities. We present an improved probabilistic atlas, incorporating thalamic nuclei identified from histology and 45 white matter tracts surrounding the thalamus identified in ultra-high gradient strength diffusion imaging. We present a family of likelihood models for diffusion tensor imaging, ensuring compatibility with the vast majority of neuroimaging datasets that include diffusion MRI data. The use of these diffusion likelihood models greatly improves identification of nuclear groups versus segmentation based solely on structural MRI. Dice comparison of 5 manually identifiable groups of nuclei to ground truth segmentations show improvements of up to 10 percentage points. Additionally, our chosen model shows a high degree of reliability, with median test-retest Dice scores above 0.85 for four out of five nuclei groups, whilst also offering improved detection of differential thalamic involvement in Alzheimer's disease (AUROC 81.98%). The probabilistic atlas and segmentation tool will be made publicly available as part of the neuroimaging package FreeSurfer (https://freesurfer.net/fswiki/ThalamicNucleiDTI).

Simulating the situated-self drives hippocampo-cortical engagement during inner narration of events.

We often use inner narration when thinking about past and future events. The present paradigm explicitly addresses the influence of the language used in inner narration on the hippocampus-dependent event construction process. We assessed the language context effect during the inner narration of different event types: past, future, daydream, and self-unrelated fictitious events. The language context was assessed via a fluent bilingual population who used inner narration, either in their first language (L1) or second language (L2). Not all inner narration of events elicited hippocampo-cortical activity. In fact, only the angular gyrus and precuneus-retrosplenial cortex were activated by inner narration across all event types. More precisely, only inner narration of events which entailed the simulation of bodily self-location in space (whether or not they were time-marked: past, future, daydream) depended on the hippocampo-cortical system, while inner narration of events that did not entail bodily self-location (self-unrelated fictitious) did not. The language context of the narration influenced the bilinguals' hippocampo-cortical system by enhancing the co-activation of semantic areas with the hippocampus for inner narration of events in the L2. Overall, this study highlights 2 important characteristics of hippocampo-cortical-dependent inner narration of events: The core episodic hippocampal system is activated for inner narration of events simulating self-location in space (regardless of time-marking), and the inner language used for narration (L1 or L2) mediates hippocampal functional connectivity.

Task-Relevant Representations and Cognitive Control Demands Modulate Functional Connectivity from Ventral Occipito-Temporal Cortex During Object Recognition Tasks.

The left ventral occipito-temporal cortex (vOTC) supports extraction and processing of visual features. However, it has remained unclear whether left vOTC-based functional connectivity (FC) differs according to task-relevant representations (e.g., lexical, visual) and control demands imposed by the task, even when similar visual-semantic processing is required for object identification. Here, neural responses to the same set of pictures of meaningful objects were measured, while the type of task that participants had to perform (picture naming versus size-judgment task), and the level of cognitive control required by the picture naming task (high versus low interference contexts) were manipulated. Explicit retrieval of lexical representations in the picture naming task facilitated activation of lexical/phonological representations, modulating FC between left vOTC and dorsal anterior-cingulate-cortex/pre-supplementary-motor-area. This effect was not observed in the size-judgment task, which did not require explicit word-retrieval of object names. Furthermore, retrieving the very same lexical/phonological representation in the high versus low interference contexts during picture naming increased FC between left vOTC and left caudate. These findings support the proposal that vOTC functional specialization emerges from interactions with task-relevant brain regions.

Reproducible protocol to obtain and measure first-order relay human thalamic white-matter tracts.

The "primary" or "first-order relay" nuclei of the thalamus feed the cerebral cortex with information about ongoing activity in the environment or the subcortical motor systems. Because of the small size of these nuclei and the high specificity of their input and output pathways, new imaging protocols are required to investigate thalamocortical interactions in human perception, cognition and language. The goal of the present study was twofold: I) to develop a reconstruction protocol based on in vivo diffusion MRI to extract and measure the axonal fiber tracts that originate or terminate specifically in individual first-order relay nuclei; and, II) to test the reliability of this reconstruction protocol. In left and right hemispheres, we investigated the thalamocortical/corticothalamic axon bundles linking each of the first-order relay nuclei and their main cortical target areas, namely, the lateral geniculate nucleus (optic radiation), the medial geniculate nucleus (acoustic radiation), the ventral posterior nucleus (somatosensory radiation) and the ventral lateral nucleus (motor radiation). In addition, we examined the main subcortical input pathway to the ventral lateral posterior nucleus, which originates in the dentate nucleus of the cerebellum. Our protocol comprised three components: defining regions-of-interest; preprocessing diffusion data; and modeling white-matter tracts and tractometry. We then used computation and test-retest methods to check whether our protocol could reliably reconstruct these tracts of interest and their profiles. Our results demonstrated that the protocol had nearly perfect computational reproducibility and good-to-excellent test-retest reproducibility. This new protocol may be of interest for both basic human brain neuroscience and clinical studies and has been made publicly available to the scientific community.

Encoding and inhibition of arbitrary episodic context with abstract concepts.

Context is critical for conceptual processing, but the mechanism underpinning its encoding and reinstantiation during abstract concept processing is unclear. Context may be especially important for abstract concepts-we investigated whether episodic context is recruited differently when processing abstract compared with concrete concepts. Experiments 1 and 2 presented abstract and concrete words in arbitrary contexts at encoding (Experiment 1: red/green colored frames; Experiment 2: male/female voices). Recognition memory for these contexts was worse for abstract concepts. Again using frame color and voice as arbitrary contexts, respectively, Experiments 3 and 4 presented words from encoding in the same or different context at test to determine whether there was a greater recognition memory benefit for abstract versus concrete concepts when the context was unchanged between encoding and test. Instead, abstract concepts were less likely to be remembered when context was retained. This suggests that at least some types of episodic context-when arbitrary-are attended less, and may even be inhibited, when processing abstract concepts. In Experiment 5, we utilized a context-spatial location-which (as we show) tends to be relevant during real-world processing of abstract concepts. We presented words in different locations, preserving or changing location at test. Location retention conferred a recognition memory advantage for abstract concepts. Thus, episodic context may be encoded with abstract concepts when context is relevant to real-world processing. The systematic contexts necessary for understanding abstract concepts may lead to arbitrary context inhibition, but greater attention to contexts that tend to be more relevant during real-world processing.

Converging Evidence for Differential Specialization and Plasticity of Language Systems.

Functional specialization and plasticity are fundamental organizing principles of the brain. Since the mid-1800s, certain cognitive functions have been known to be lateralized, but the provenance and flexibility of hemispheric specialization remain open questions. Language is a uniquely human phenomenon that requires a delicate balance between neural specialization and plasticity, and language learning offers the perfect window to study these principles in the human brain. In the current study, we conducted two separate functional MRI experiments with language learners (male and female), one cross-sectional and one longitudinal, involving distinct populations and languages, and examined hemispheric lateralization and learning-dependent plasticity of the following three language systems: reading, speech comprehension, and verbal production. A multipronged analytic approach revealed a highly consistent pattern of results across the two experiments, showing (1) that in both native and non-native languages, while language production was left lateralized, lateralization for language comprehension was highly variable across individuals; and (2) that with increasing non-native language proficiency, reading and speech comprehension displayed substantial changes in hemispheric dominance, with languages tending to lateralize to opposite hemispheres, while production showed negligible change and remained left lateralized. These convergent results shed light on the long-standing debate of neural organization of language by establishing robust principles of lateralization and plasticity of the main language systems. Findings further suggest involvement of the sensorimotor systems in language lateralization and its plasticity.SIGNIFICANCE STATEMENT The human brain exhibits a remarkable ability to support a vast variety of languages that may be acquired at different points in the life span. Language is a complex construct involving linguistic as well as visual, auditory, and motor processes. Using functional MRI, we examined hemispheric specialization and learning-dependent plasticity of three language systems-reading, speech comprehension, and verbal production-in cross-sectional and longitudinal experiments in language learners. A multipronged analytic approach revealed converging evidence for striking differences in hemispheric specialization and plasticity among the language systems. The results have major theoretical and practical implications for our understanding of fundamental principles of neural organization of language, language testing and recovery in patients, and language learning in healthy populations.

Converging evidence for functional and structural segregation within the left ventral occipitotemporal cortex in reading.

The ventral occipitotemporal cortex (vOTC) is crucial for recognizing visual patterns, and previous evidence suggests that there may be different subregions within the vOTC involved in the rapid identification of word forms. Here, we characterize vOTC reading circuitry using a multimodal approach combining functional, structural, and quantitative MRI and behavioral data. Two main word-responsive vOTC areas emerged: a posterior area involved in visual feature extraction, structurally connected to the intraparietal sulcus via the vertical occipital fasciculus; and an anterior area involved in integrating information with other regions of the language network, structurally connected to the angular gyrus via the posterior arcuate fasciculus. Furthermore, functional activation in these vOTC regions predicted reading behavior outside of the scanner. Differences in the microarchitectonic properties of gray-matter cells in these segregated areas were also observed, in line with earlier cytoarchitectonic evidence. These findings advance our understanding of the vOTC circuitry by linking functional responses to anatomical structure, revealing the pathways of distinct reading-related processes.

Functional connectivity reveals dissociable ventrolateral prefrontal mechanisms for the control of multilingual word retrieval.

This functional magnetic resonance imaging study established that different portions of the ventrolateral prefrontal cortex (vlPFC) support reactive and proactive language control processes during multilingual word retrieval. The study also examined whether proactive language control consists in the suppression of the nontarget lexicon. Healthy multilingual volunteers participated in a task that required them to name pictures alternately in their dominant and less-dominant languages. Two crucial variables were manipulated: the cue-target interval (CTI) to either engage (long CTI) or prevent (short CTI) proactive control processes, and the cognate status of the to-be-named pictures (noncognates vs. cognates) to capture selective pre-activation of the target language. The results of the functional connectivity analysis showed a clear segregation between functional networks related to mid-vlPFC and anterior vlPFC during multilingual language production. Furthermore, the results revealed that multilinguals engage in proactive control to prepare the target language. This proactive modulation, enacted by anterior vlPFC, is achieved by boosting the activation of lexical representations in the target language. Finally, control processes supported by both mid-vlPFC and the left inferior parietal lobe, were similarly engaged by reactive and proactive control, possibly exerted on phonological representations to reduce cross-language interference.

Functional inhibitory control dynamics in impulse control disorders in Parkinson's disease.

BACKGROUND: Impulse control disorders related to alterations in the mesocorticolimbic dopamine network occur in Parkinson's disease (PD). Our objective was to investigate the functional neural substrates of reward processing and inhibitory control in these patients. METHODS: Eighteen PD patients with impulse control disorders, 17 without this complication, and 18 healthy controls performed a version of the Iowa Gambling Task during functional magnetic resonance scanning under 3 conditions: positive, negative, and mixed feedback. Whole-brain contrasts, regions of interest, time courses, functional connectivity analyses, and brain-behavior associations were examined. RESULTS: PD patients with impulse control disorders exhibited hyperactivation in subcortical and cortical regions typically associated with reward processing and inhibitory control compared with their PD and healthy control counterparts. Time-course analyses revealed that only PD patients with impulse control disorders exhibited stronger signal intensity during the initial versus final periods of the negative-feedback condition in bilateral insula, and right ventral striatum. Interestingly, hyperactivation of all the examined right-lateralized frontostriatal areas during negative feedback was positively associated with impulse control disorder severity. Importantly, positive associations between impulse control disorder severity and regional activations in the right insula and right inferior frontal gyrus, but not the right subthalamic nucleus, were mediated by functional connectivity with the right ventral striatum. CONCLUSIONS: During a reward-based task, PD patients with impulse control disorders showed hyperactivation in a right-lateralized network of regions including the subthalamic nucleus that was strongly associated with impulse control disorder severity. In these patients, the right ventral striatum in particular played a critical role in modulating the functional dynamics of right-lateralized inhibitory-control frontal regions when facing penalties. © 2019 International Parkinson and Movement Disorder Society.

Connectivity of Frontoparietal Regions Reveals Executive Attention and Consciousness Interactions.

The executive control network is involved in the voluntary control of novel and complex situations. Solving conflict situations or detecting errors have demonstrated to impair conscious perception of near-threshold stimuli. The aim of this study was to explore the neural mechanisms underlying executive control and its interaction with conscious perception using functional magnetic resonance imaging and diffusion-weighted imaging. To this end, we used a dual-task paradigm involving Stroop and conscious detection tasks with near-threshold stimuli. A set of prefrontal and frontoparietal regions were more strongly engaged for incongruent than congruent trials while a distributed set of frontoparietal regions showed stronger activation for consciously than nonconsciously perceived trials. Functional connectivity analysis revealed an interaction between executive control and conscious perception in frontal and parietal nodes. The microstructural properties of the middle branch of the superior longitudinal fasciculus were associated with neural measures of the interaction between executive control and consciousness. These results demonstrate that conscious perception and executive control share neural resources in frontoparietal networks, as proposed by some influential models.

Functional plasticity associated with language learning in adults.

Learning a new language in adulthood is increasingly common and among the most difficult tasks attempted by adults. Adult language learners thus offer an excellent window into the nature of learning-dependent plasticity. The present functional magnetic resonance imaging (fMRI) study was aimed at characterising functional neuroplasticity in adults at different stages of learning a second language (L2). To this end, a total of 34 adults, either intermediate or advanced L2 learners, underwent MRI scanning while performing a semantic judgement task with print and speech stimuli. Three separate analytical approaches were used to comprehensively map neural differences: print-speech convergence, L1-L2 similarity, and functional connectivity with language control regions. Results revealed that (i) print-speech convergence was not affected by L2 proficiency level, (ii) L1-L2 similarity was significantly higher in intermediate than in advanced L2 learners, and (iii) functional coupling of language and language control areas was higher in the advanced relative to the intermediate group during reading comprehension. The results point to significant functional differences between intermediate and advanced language learners, indicating that, even well into adulthood, increasing L2 proficiency modulates the functional similarity between L1 and L2 and the connectivity between language comprehension and language control regions, particularly in reading comprehension.

Metacognitive scaffolding boosts cognitive and neural benefits following executive attention training in children.

Interventions including social scaffolding and metacognitive strategies have been used in educational settings to promote cognition. In addition, increasing evidence shows that computerized process-based training enhances cognitive skills. However, no prior studies have examined the effect of combining these two training strategies. The goal of this study was to test the combined effect of metacognitive scaffolding and computer-based training of executive attention in a sample of typically developing preschoolers at the cognitive and brain levels. Compared to children in the regular training protocol and an untrained active control group, children in the metacognitive group showed larger gains on intelligence and significant increases on an electrophysiological index associated with conflict processing. Moreover, changes in the conflict-related brain activity predicted gains in intelligence in the metacognitive scaffolding group. These results suggest that metacognitive scaffolding boosts the influence of process-based training on cognitive efficiency and brain plasticity related to executive attention.

A probabilistic atlas of the human thalamic nuclei combining ex vivo MRI and histology.

The human thalamus is a brain structure that comprises numerous, highly specific nuclei. Since these nuclei are known to have different functions and to be connected to different areas of the cerebral cortex, it is of great interest for the neuroimaging community to study their volume, shape and connectivity in vivo with MRI. In this study, we present a probabilistic atlas of the thalamic nuclei built using ex vivo brain MRI scans and histological data, as well as the application of the atlas to in vivo MRI segmentation. The atlas was built using manual delineation of 26 thalamic nuclei on the serial histology of 12 whole thalami from six autopsy samples, combined with manual segmentations of the whole thalamus and surrounding structures (caudate, putamen, hippocampus, etc.) made on in vivo brain MR data from 39 subjects. The 3D structure of the histological data and corresponding manual segmentations was recovered using the ex vivo MRI as reference frame, and stacks of blockface photographs acquired during the sectioning as intermediate target. The atlas, which was encoded as an adaptive tetrahedral mesh, shows a good agreement with previous histological studies of the thalamus in terms of volumes of representative nuclei. When applied to segmentation of in vivo scans using Bayesian inference, the atlas shows excellent test-retest reliability, robustness to changes in input MRI contrast, and ability to detect differential thalamic effects in subjects with Alzheimer's disease. The probabilistic atlas and companion segmentation tool are publicly available as part of the neuroimaging package FreeSurfer.

Functional Dynamics of Dorsal and Ventral Reading Networks in Bilinguals.

In today's world, bilingualism is increasingly common. However, it is still unclear how left-lateralized dorsal and ventral reading networks are tuned to reading in proficient second-language learners. Here, we investigated differences in functional regional activation and connectivity as a function of L1 and L2 reading, L2 orthographic depth, and task demands. Thirty-seven late bilinguals with the same L1 and either an opaque or transparent L2 performed perceptual and semantic reading tasks in L1 and L2 during functional magnetic resonance imaging (fMRI) scanning. Results revealed stronger regional recruitment for L2 versus L1 reading and stronger connectivity within the dorsal stream during L1 versus L2 reading. Differences in orthographic depth were associated with a segregated profile of left ventral occipitotemporal (vOT) coactivation with dorsal regions for the transparent L2 group and with ventral regions for the opaque L2 group. Finally, semantic versus perceptual demands modulated left vOT engagement, supporting the interactive account of the contribution of vOT to reading, and were associated with stronger coactivation within the ventral network. Our findings support a division of labor between ventral and dorsal reading networks, elucidating the critical role of the language used to read, L2 orthographic depth, and task demands on the functional dynamics of bilingual reading.

Universal brain signature of proficient reading: Evidence from four contrasting languages.

We propose and test a theoretical perspective in which a universal hallmark of successful literacy acquisition is the convergence of the speech and orthographic processing systems onto a common network of neural structures, regardless of how spoken words are represented orthographically in a writing system. During functional MRI, skilled adult readers of four distinct and highly contrasting languages, Spanish, English, Hebrew, and Chinese, performed an identical semantic categorization task to spoken and written words. Results from three complementary analytic approaches demonstrate limited language variation, with speech-print convergence emerging as a common brain signature of reading proficiency across the wide spectrum of selected languages, whether their writing system is alphabetic or logographic, whether it is opaque or transparent, and regardless of the phonological and morphological structure it represents.