Effective connectivity of the left BA 44, BA 45, and inferior temporal gyrus during lexical and phonological decisions identified with DCM

Direct Retrieval of Orthographic Representations in Chinese Handwritten Production: Evidence from a Dynamic Causal Modeling Study

This present study identified an optimal model representing the relationship between orthography and phonology in Chinese handwritten production using dynamic causal modeling, and further explored how this model was modulated by word frequency and syllable frequency. Each model contained five volumes of interest in the left hemisphere (angular gyrus [AG], inferior frontal gyrus [IFG], middle frontal gyrus [MFG], superior frontal gyrus [SFG], and supramarginal gyrus [SMG]), with the IFG as the driven input area. Results showed the superiority of a model in which both the MFG and the AG connected with the IFG, supporting the orthography autonomy hypothesis. Word frequency modulated the AG → SFG connection (information flow from the orthographic lexicon to the orthographic buffer), and syllable frequency affected the IFG → MFG connection (information transmission from the semantic system to the phonological lexicon). This study thus provides new insights into the connectivity architecture of neural substrates involved in writing.

The angular gyrus serves as an interface between the non-lexical reading network and the semantic system: evidence from dynamic causal modeling

Understanding encoded language, such as written words, requires multiple cognitive processes that act in a parallel and interactive fashion. These processes and their interactions, however, are not fully understood. Various conceptual and methodical approaches including computational modeling and neuroimaging have been applied to better understand the neural underpinnings of these complex processes in the human brain. In this study, we tested different predictions of cortical interactions that derived from computational models for reading using dynamic causal modeling. Morse code was used as a model for non-lexical decoding followed by a lexical-decision during a functional magnetic resonance examination. Our results suggest that individual letters are first converted into phonemes within the left supramarginal gyrus, followed by a phoneme assembly to reconstruct word phonology, involving the left inferior frontal cortex. To allow the identification and comprehension of known words, the inferior frontal cortex then interacts with the semantic system via the left angular gyrus. As such, the left angular gyrus is likely to host phonological and semantic representations and serves as a bidirectional interface between the networks involved in language perception and word comprehension.

Inter- and intra- hemispheric interactions in reading ambiguous words

The present study investigated how the brain processes words with multiple meanings. Specifically, we examined the inter- and intra-hemispheric connectivity of unambiguous words compared to two types of ambiguous words: homophonic homographs, which have multiple meanings mapped to a single phonological representation and orthography, and heterophonic homographs, which have multiple meanings mapped to different phonological representations but the same orthography. Using a semantic relatedness judgment task and effective connectivity analysis via Dynamic Causal Modeling (DCM) on previously published fMRI data (Bitan et al., 2017), we found that the two hemispheres compete in orthographic processing during the reading of unambiguous words. For heterophonic homographs, we observed increased connectivity within the left hemisphere, highlighting the importance of top-down re-activation of orthographic representations by phonological ones for considering alternative meanings. For homophonic homographs, we found a flow of information from the left to the right hemisphere and from the right to the left, indicating that the brain retrieves different meanings using different pathways. These findings provide novel insights into the complex mechanisms involved in language processing and shed light on the different communication patterns within and between hemispheres during the processing of ambiguous and unambiguous words.

Understanding the concept of a novel tool requires interaction of the dorsal and ventral streams

The left hemisphere tool-use network consists of the dorso-dorsal, ventro-dorsal, and ventral streams, each with distinct computational abilities. In the dual-loop model, the ventral pathway through the extreme capsule is associated with conceptual understanding. We performed a learning experiment with fMRI to investigate how these streams interact when confronted with novel tools. In session one, subjects observed pictures and video sequences in real world action of known and unknown tools and were asked whether they knew the tools and whether they understood their function. In session two, video sequences of unknown tools were presented again, followed again by the question of understanding their function. Different conditions were compared to each other and effective connectivity (EC) in the tool-use network was examined. During concept acquisition of an unknown tool, EC between dorsal and ventral streams was found posterior in fusiform gyrus and anterior in inferior frontal gyrus, with a functional interaction between BA44d and BA45. When previously unknown tools were presented for a second time, EC was prominent only between dorsal stream areas. Understanding the concept of a novel tool requires an interaction of the ventral stream with the dorsal streams. Once the concept is acquired, dorsal stream areas are sufficient.

Neural evidence suggests phonological acceptability judgments reflect similarity, not constraint evaluation

Acceptability judgments are a primary source of evidence in formal linguistic research. Within the generative linguistic tradition, these judgments are attributed to evaluation of novel forms based on implicit knowledge of rules or constraints governing well-formedness. In the domain of phonological acceptability judgments, other factors including ease of articulation and similarity to known forms have been hypothesized to influence evaluation. We used data-driven neural techniques to identify the relative contributions of these factors. Granger causality analysis of magnetic resonance imaging (MRI)-constrained magnetoencephalography (MEG) and electroencephalography (EEG) data revealed patterns of interaction between brain regions that support explicit judgments of the phonological acceptability of spoken nonwords. Comparisons of data obtained with nonwords that varied in terms of onset consonant cluster attestation and acceptability revealed different cortical regions and effective connectivity patterns associated with phonological acceptability judgments. Attested forms produced stronger influences of brain regions implicated in lexical representation and sensorimotor simulation on acoustic-phonetic regions, whereas unattested forms produced stronger influence of phonological control mechanisms on acoustic-phonetic processing. Unacceptable forms produced widespread patterns of interaction consistent with attempted search or repair. Together, these results suggest that speakers' phonological acceptability judgments reflect lexical and sensorimotor factors.

Evaluation of a Simple Clinical Language Paradigm With Respect to Sensory Independency, Functional Asymmetry, and Effective Connectivity

The present study replicates a known visual language paradigm, and extends it to a paradigm that is independent from the sensory modality of the stimuli and, hence, could be administered either visually or aurally, such that both patients with limited sight or hearing could be examined. The stimuli were simple sentences, but required the subject not only to understand the content of the sentence but also to formulate a response that had a semantic relation to the content of the presented sentence. Thereby, this paradigm does not only test perception of the stimuli, but also to some extend sentence and semantic processing, and covert speech production within one task. When the sensory base-line condition was subtracted, both the auditory and visual version of the paradigm demonstrated a broadly overlapping and asymmetric network, comprising distinct areas of the left posterior temporal lobe, left inferior frontal areas, left precentral gyrus, and supplementary motor area. The consistency of activations and their asymmetry was evaluated with a conjunction analysis, probability maps, and intraclass correlation coefficients (ICC). This underlying network was further analyzed with dynamic causal modeling (DCM) to explore whether not only the same brain areas were involved, but also the network structure and information flow were the same between the sensory modalities. In conclusion, the paradigm reliably activated the most central parts of the speech and language network with a great consistency across subjects, and independently of whether the stimuli were administered aurally or visually. However, there was individual variability in the degree of functional asymmetry between the two sensory conditions.

Is There a Difference in Brain Functional Connectivity between Chinese Coal Mine Workers Who Have Engaged in Unsafe Behavior and Those Who Have Not?

(1) Background: As a world-recognized high-risk occupation, coal mine workers need various cognitive functions to process the surrounding information to cope with a large number of perceived hazards or risks. Therefore, it is necessary to explore the connection between coal mine workers’ neural activity and unsafe behavior from the perspective of cognitive neuroscience. This study explored the functional brain connectivity of coal mine workers who have engaged in unsafe behaviors (EUB) and those who have not (NUB). (2) Methods: Based on functional near-infrared spectroscopy (fNIRS), a total of 106 workers from the Hongliulin coal mine of Shaanxi North Mining Group, one of the largest modern coal mines in China, completed the test. Pearson’s Correlation Coefficient (COR) analysis, brain network analysis, and two-sample t-test were used to investigate the difference in brain functional connectivity between the two groups. (3) Results: The results showed that there were significant differences in functional brain connectivity between EUB and NUB among the frontopolar area (p = 0.002325), orbitofrontal area (p = 0.02102), and pars triangularis Broca’s area (p = 0.02888). Small-world properties existed in the brain networks of both groups, and the dorsolateral prefrontal cortex had significant differences in clustering coefficient (p = 0.0004), nodal efficiency (p = 0.0384), and nodal local efficiency (p = 0.0004). (4) Conclusions: This study is the first application of fNIRS to the field of coal mine safety. The fNIRS brain functional connectivity analysis is a feasible method to investigate the neuropsychological mechanism of unsafe behavior in coal mine workers in the view of brain science.

Simultaneous Normalization and Compensatory Changes in Right Hemisphere Connectivity during Aphasia Therapy

Changes in brain connectivity during language therapy were examined among participants with aphasia (PWA), aiming to shed light on neural reorganization in the language network. Four PWA with anomia following left hemisphere stroke and eight healthy controls (HC) participated in the study. Two fMRI scans were administered to all participants with a 3.5-month interval. The fMRI scans included phonological and semantic tasks, each consisting of linguistic and perceptual matching conditions. Between the two fMRI scans, PWA underwent Phonological Components Analysis treatment. Changes in effective connectivity during the treatment were examined within right hemisphere (RH) architecture. The results illustrate that following the treatment, the averaged connectivity of PWA across all perceptual and linguistic conditions in both tasks increased resemblance to HC, reflecting the normalization of neural processes associated with silent object name retrieval. In contrast, connections that were specifically enhanced by the phonological condition in PWA decreased in their resemblance to HC, reflecting emerging compensatory reorganization in RH connectivity to support phonological processing. These findings suggest that both normalization and compensation play a role in neural language reorganization at the chronic stage, occurring simultaneously in the same brain.

What to Believe? Impact of Knowledge and Message Length on Neural Activity in Message Credibility Evaluation

Understanding how humans evaluate credibility is an important scientific question in the era of fake news. Message credibility is among crucial aspects of credibility evaluations. One of the most direct ways to understand message credibility is to use measurements of brain activity of humans performing credibility evaluations. Nevertheless, message credibility has never been investigated using such a method before. This article reports the results of an experiment during which we have measured brain activity during message credibility evaluation, using EEG. The experiment allowed for identification of brain areas that were active when participant made positive or negative message credibility evaluations. Based on experimental data, we modeled and predicted human message credibility evaluations using EEG brain activity measurements with F1 score exceeding 0.7.

Effective connectivity underlying reward-based executive control

Motivational influences on cognitive control play an important role in shaping human behavior. Cognitive facilitation through motivators such as prospective reward or punishment is thought to depend on regions from the dopaminergic mesocortical network, primarily the ventral tegmental area (VTA), inferior frontal junction (IFJ), and anterior cingulate cortex (ACC). However, how interactions between these regions relate to motivated control remains elusive. In the present functional magnetic resonance imaging study, we used dynamic causal modeling (DCM) to investigate effective connectivity between left IFJ, ACC, and VTA in a task-switching paradigm comprising three distinct motivational conditions (prospective monetary reward or punishment and a control condition). We found that while prospective punishment significantly facilitated switching between tasks on a behavioral level, interactions between IFJ, ACC, and VTA were characterized by modulations through prospective reward but not punishment. Our DCM results show that IFJ and VTA modulate ACC activity in parallel rather than by interaction to serve task demands in reward-based cognitive control. Our findings further demonstrate that prospective reward and punishment differentially affect neural control mechanisms to initiate decision-making.

Functional Activation and Connectivity of the Left Inferior Frontal Gyrus during Lexical and Phonological Retrieval

Being language a paradigm of structural and functional asymmetry in cognitive processing, the left Inferior Frontal Gyrus has been consistently related to speech production. In fact, it has been considered a key node in cortical networks responsible for different components of naming. However, isolating these components (e.g., lexical, syntactic, and phonological retrieval) in neuroimaging studies is difficult due to the use of different baselines and tasks. In the present study, functional activation and connectivity of the left inferior frontal gyrus was explored using functional magnetic resonance imaging. Participants performed a covert naming task (pressing a button based on a phonological characteristic). Two conditions were compared: drawings of objects and single letters (baseline condition). Differences in activation and functional connectivity were obtained for objects and letters in different areas of the left Inferior Frontal Gyrus. The pars triangularis was involved in the retrieval of lexical-phonological information, showing a pattern of connectivity with temporal areas in the search for the name of objects and with perisylvanian areas for letters. Selection of phonological information seems to involve the pars opercularis both to letters and objects but recruiting supramarginal and superior temporal areas to letters, probably related to orthographic-phonological conversion. The results support the notion of the left Inferior Frontal Gyrus as a buffer forwarding neural information across cortical networks responsible for different components of speech production.

Identification of Phonology-Related Genes and Functional Characterization of Broca's and Wernicke's Regions in Language and Learning Disorders

Impaired phonological processing is a leading symptom of multifactorial language and learning disorders suggesting a common biological basis. Here we evaluated studies of dyslexia, dyscalculia, specific language impairment (SLI), and the logopenic variant of primary progressive aphasia (lvPPA) seeking for shared risk genes in Broca's and Wernicke's regions, being key for phonological processing within the complex language network. The identified "phonology-related genes" from literature were functionally characterized using Atlas-based expression mapping (JuGEx) and gene set enrichment. Out of 643 publications from the last decade until now, we extracted 21 candidate genes of which 13 overlapped with dyslexia and SLI, six with dyslexia and dyscalculia, and two with dyslexia, dyscalculia, and SLI. No overlap was observed between the childhood disorders and the late-onset lvPPA often showing symptoms of learning disorders earlier in life. Multiple genes were enriched in Gene Ontology terms of the topics learning (CNTNAP2, CYFIP1, DCDC2, DNAAF4, FOXP2) and neuronal development (CCDC136, CNTNAP2, CYFIP1, DCDC2, KIAA0319, RBFOX2, ROBO1). Twelve genes showed above-average expression across both regions indicating moderate-to-high gene activity in the investigated cortical part of the language network. Of these, three genes were differentially expressed suggesting potential regional specializations: ATP2C2 was upregulated in Broca's region, while DNAAF4 and FOXP2 were upregulated in Wernicke's region. ATP2C2 encodes a magnesium-dependent calcium transporter which fits with reports about disturbed calcium and magnesium levels for dyslexia and other communication disorders. DNAAF4 (formerly known as DYX1C1) is involved in neuronal migration supporting the hypothesis of disturbed migration in dyslexia. FOXP2 is a transcription factor that regulates a number of genes involved in development of speech and language. Overall, our interdisciplinary and multi-tiered approach provided evidence that genetic and transcriptional variation of ATP2C2, DNAAF4, and FOXP2 may play a role in physiological and pathological aspects of phonological processing.

Common and specific neural correlates underlying insight and ordinary problem solving

Previous studies have investigated the cognitive and neural mechanisms underlying insight problem solving (INPS). However, it is still unclear which mechanisms are common to both INPS and ordinary problem solving (ORPS), and which are distinctly involved in only one of these processes. In this study, we selected two types of Chinese character chunk decompositions, ordinary Chinese character chunk decomposition (OCD) and creative Chinese character chunk decomposition (CCD), as representatives of ORPS and INPS, respectively. By using functional magnetic resonance imaging (fMRI) to record brain activations when subjects executed OCD or CCD operations, we found that both ORPS and INPS resulted in significant activations in the widespread frontoparietal cognitive control network, including the middle frontal gyrus, inferior frontal gyrus, and inferior parietal lobe. Furthermore, compared with ORPS, INPS led to greater activations in higher-level brain regions related to symbolic processing in the default mode network, including the anterior cingulate cortex, superior temporal gyrus, angular gyrus, and precuneus. Conversely, ORPS induced greater activations than INPS in more posterior brain regions related to visuospatial attention and visual perception, such as the inferior temporal gyrus, hippocampus, and middle occipital gyrus/superior parietal gyrus/fusiform gyrus. In addition, an ROI analysis corroborated the neural commonalities and differences between ORPS and INPS. These findings provide new evidence that ORPS and INPS rely on common as well as distinct cognitive processes and cortical mechanisms.

Neural correlates of visual stimulus encoding and verbal working memory differ between cochlear implant users and normal-hearing controls

A common concern for individuals with severe‐to‐profound hearing loss fitted with cochlear implants (CIs) is difficulty following conversations in noisy environments. Recent work has suggested that these difficulties are related to individual differences in brain function, including verbal working memory and the degree of cross‐modal reorganization of auditory areas for visual processing. However, the neural basis for these relationships is not fully understood. Here, we investigated neural correlates of visual verbal working memory and sensory plasticity in 14 CI users and age‐matched normal‐hearing (NH) controls. While we recorded the high‐density electroencephalogram (EEG), participants completed a modified Sternberg visual working memory task where sets of letters and numbers were presented visually and then recalled at a later time. Results suggested that CI users had comparable behavioural working memory performance compared with NH. However, CI users had more pronounced neural activity during visual stimulus encoding, including stronger visual‐evoked activity in auditory and visual cortices, larger modulations of neural oscillations and increased frontotemporal connectivity. In contrast, during memory retention of the characters, CI users had descriptively weaker neural oscillations and significantly lower frontotemporal connectivity. We interpret the differences in neural correlates of visual stimulus processing in CI users through the lens of cross‐modal and intramodal plasticity.

Electrocorticography reveals spatiotemporal neuronal activation patterns of verbal fluency in patients with epilepsy

Verbal fluency is commonly used to evaluate cognitive dysfunction in a variety of neuropsychiatric diseases, yet the neurobiology underlying performance of this task is incompletely understood. Electrocorticography (ECoG) provides a unique opportunity to investigate temporal activation patterns during cognitive tasks with high spatial and temporal precision. We used ECoG to study high gamma activity (HGA) patterns in patients undergoing presurgical evaluation for intractable epilepsy as they completed an overt, free-recall verbal fluency task. We examined regions demonstrating changes in HGA during specific timeframes relative to speech onset. Early pre-speech high gamma activity was present in left frontal regions during letter fluency and in bifrontal regions during category fluency. During timeframes typically associated with word planning, a distributed network was engaged including left inferior frontal, orbitofrontal and posterior temporal regions. Peri-Rolandic activation was observed during speech onset, and there was post-speech activation in the bilateral posterior superior temporal regions. Based on these observations in the context of prior studies, we propose a model of neocortical activity patterns underlying verbal fluency.

Aging-related differences in the cortical network subserving intelligible speech

Language communication is crucial throughout the lifespan. The current study investigated how aging affects the brain network subserving intelligible speech. Using functional magnetic resonance imaging, we compared brain responses to intelligible and unintelligible speech between older and young adults. Univariate and multivariate analyses revealed reduced brain activation and lower regional pattern distinctions in response to intelligible versus unintelligible speech in the left anterior superior temporal gyrus (aSTG) and the left inferior frontal gyrus (IFG) in the older compared with young adults. Notably, the functional connectivity between the left IFG and the left angular gyrus (AG) was increased and a significantly enhanced bidirectional effective connectivity between the left aSTG and the left AG was observed in the older adults for processing speech intelligibility. Our study revealed aging-related differences in the cortical activity for intelligible speech and suggested that increased frontal-temporal-parietal functional integration may help facilitate spoken language processing in older adults.

Correlation between diffusion tensor imaging measures and the reading and cognitive performance of Arabic readers: dyslexic children perspective

PURPOSE

To investigate the correlation between the diffusion tensor imaging (DTI) measures and the reading, spelling, writing, rapid naming, memory, and motor abilities in Arabic dyslexic children. This could verify the influence of possible white matter alterations on the abilities of those children.

METHODS

Twenty native Arabic-speaking children with dyslexia (15 males and 5 females; 8.2 years ± 1) underwent DTI of the brain on 1.5 T scanner. Diffusion-weighted images were acquired in 32 noncollinear direction. Tractography of the arcuate fasciculus (AF) was performed. Region of interest (ROI)-based approach was also used. Regions encompass superior longitudinal fasciculus (SLF), anterior and superior corona radiata (CR), and posterior limb of internal capsule (PLIC) were analyzed. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured. The aptitudes of those children were evaluated by the dyslexia assessment test. These abilities were statistically correlated with the FA and ADC of the AF and other ROIs.

RESULTS

The reduction of FA of right AF was related to worse overall reading and related abilities performance. The ADC of right SLF was negatively correlated with memory abilities. The ADC of right PLIC was positively correlated with writing performance. Other relations were also found.

CONCLUSION

White matter microstructural DTI measurements in the right AF, right PLIC, SLF, and left anterior and superior CR are correlated to reading, spelling, writing, memory, and rapid naming abilities of the participants. The DTI measures could be promising regarding their use as a biomarker for follow-up in developmental dyslexia.

Network dynamics of Broca's area during word selection

Current models of word-production in Broca's area (i.e. left ventro-lateral prefrontal cortex, VLPFC) posit that sequential and staggered semantic, lexical, phonological and articulatory processes precede articulation. Using millisecond-resolution intra-cranial recordings, we evaluated spatiotemporal dynamics and high frequency functional interconnectivity between left VLPFC regions during single-word production. Through the systematic variation of retrieval, selection, and phonological loads, we identified specific activation profiles and functional coupling patterns between these regions that fit within current psycholinguistic theories of word production. However, network interactions underpinning these processes activate in parallel (not sequentially), while the processes themselves are indexed by specific changes in network state. We found evidence that suggests that pars orbitalis is coupled with pars triangularis during lexical retrieval, while lexical selection is terminated via coupled activity with M1 at articulation onset. Taken together, this work reveals that speech production relies on very specific inter-regional couplings in rapid sequence in the language dominant hemisphere.

Dopaminergic modulation of motor network compensatory mechanisms in Parkinson's disease

The dopaminergic system has a unique gating function in the initiation and execution of movements. When the interhemispheric imbalance of dopamine inherent to the healthy brain is disrupted, as in Parkinson's disease (PD), compensatory mechanisms act to stave off behavioral changes. It has been proposed that two such compensatory mechanisms may be (a) a decrease in motor lateralization, observed in drug-naïve PD patients and (b) reduced inhibition - increased facilitation. Seeking to investigate the differential effect of dopamine depletion and subsequent substitution on compensatory mechanisms in non-drug-naïve PD, we studied 10 PD patients and 16 healthy controls, with patients undergoing two test sessions - "ON" and "OFF" medication. Using a simple visually-cued motor response task and fMRI, we investigated cortical motor activation - in terms of laterality, contra- and ipsilateral percent BOLD signal change and effective connectivity in the parametric empirical Bayes framework. We found that decreased motor lateralization persists in non-drug-naïve PD and is concurrent with decreased contralateral activation in the cortical motor network. Normal lateralization is not reinstated by dopamine substitution. In terms of effective connectivity, disease-related changes primarily affect ipsilaterally-lateralized homotopic cortical motor connections, while medication-related changes affect contralaterally-lateralized homotopic connections. Our findings suggest that, in non-drug-naïve PD, decreased lateralization is no longer an adaptive cortical mechanism, but rather the result of maladaptive changes, related to disease progression and long-term dopamine replacement. These findings highlight the need for the development of noninvasive therapies, which would promote the adaptive mechanisms of the PD brain.

Transdiagnostic variations in impulsivity and compulsivity in obsessive-compulsive disorder and gambling disorder correlate with effective connectivity in cortical-striatal-thalamic-cortical circuits

Individual differences in impulsivity and compulsivity is thought to underlie vulnerability to a broad range of disorders and are closely tied to cortical-striatal-thalamic-cortical function. However, whether impulsivity and compulsivity in clinical disorders is continuous with the healthy population and explains cortical-striatal-thalamic-cortical dysfunction across different disorders remains unclear. Here, we characterized the relationship between cortical-striatal-thalamic-cortical effective connectivity, estimated using dynamic causal modelling of resting-state functional magnetic resonance imaging data, and dimensional phenotypes of impulsivity and compulsivity in two symptomatically distinct but phenotypically related disorders, obsessive-compulsive disorder and gambling disorder. 487 online participants provided data for modelling of dimensional phenotypes. These data were combined with 34 obsessive-compulsive disorder patients, 22 gambling disorder patients, and 39 healthy controls, who underwent functional magnetic resonance imaging. Three core dimensions were identified: disinhibition, impulsivity, and compulsivity. Patients' scores on these dimensions were continuously distributed with the healthy participants, supporting a continuum model of psychopathology. Across all participants, higher disinhibition correlated with lower bottom-up connectivity in the dorsal circuit and greater bottom-up connectivity in the ventral circuit, and higher compulsivity correlated with lower bottom-up connectivity in the dorsal circuit. In patients, higher clinical severity was also linked to lower bottom-up connectivity in the dorsal circuit, but these findings were independent of phenotypic variation, demonstrating convergence towards behaviourally and clinically relevant changes in brain dynamics. Effective connectivity did not differ as a function of traditional diagnostic labels and only weak associations were observed for functional connectivity measures. Together, our results demonstrate that cortical-striatal-thalamic-cortical dysfunction across obsessive-compulsive disorder and gambling disorder may be better characterized by dimensional phenotypes than diagnostic comparisons, supporting investigation of quantitative liability phenotypes.

A new computational approach to estimate whole-brain effective connectivity from functional and structural MRI, applied to language development

Recently introduced effective connectivity methods allow for the in-vivo investigation of large-scale functional interactions between brain regions. However, dynamic causal modeling, the most widely used technique to date, typically captures only a few predefined regions of interest. In this study, we present an alternative computational approach to infer effective connectivity within the entire connectome and show its performance on a developmental cohort with emerging language capacities. The novel approach provides new opportunities to quantify effective connectivity changes in the human brain.

Consistent Gradient of Performance and Decoding of Stimulus Type and Valence From Local and Network Activity

The individual differences approach focuses on the variation of behavioral and neural signatures across subjects. In this context, we searched for intracranial neural markers of performance in three individuals with distinct behavioral patterns (efficient, borderline, and inefficient) in a dual-valence task assessing facial and lexical emotion recognition. First, we performed a preliminary study to replicate well-established evoked responses in relevant brain regions. Then, we examined time series data and network connectivity, combined with multivariate pattern analyses and machine learning, to explore electrophysiological differences in resting-state versus task-related activity across subjects. Next, using the same methodological approach, we assessed the neural decoding of performance for different dimensions of the task. The classification of time series data mirrored the behavioral gradient across subjects for stimulus type but not for valence. However, network-based measures reflected the subjects' hierarchical profiles for both stimulus types and valence. Therefore, this measure serves as a sensitive marker for capturing distributed processes such as emotional valence discrimination, which relies on an extended set of regions. Network measures combined with classification methods may offer useful insights to study single subjects and understand inter-individual performance variability. Promisingly, this approach could eventually be extrapolated to other neuroscientific techniques.

Neural substrates of word category information as the basis of syntactic processing

The ability to use word category information (WCI) for syntactic structure building has been hypothesized to be the essence of human language faculty. The neural substrate of the ability of using the WCI for the complex syntactic hierarchical structure processing, however, is yet unknown. Therefore, we directly conducted an fMRI experiment by using a pseudo-Chinese artificial language with syntactic structures containing a center-embedded relative clause. Thirty non-Chinese native (Korean) speakers were randomly divided into two groups: one acquired WCI and WCI-based syntactic rules (the WCI group) before the scanning session, and the other did not (the non-WCI group). Both groups were required to judge the grammaticality of the testing sentences, with critical long-distance dependencies between two elements (the main verb and the relativizer). Behaviorally, the WCI group's accuracy was significantly higher and its reaction time was shorter. The scanning results showed that the left superior temporal gyrus (STG) and Broca's area were more strongly activated for the WCI group, and the dynamic causal modeling analyses revealed a distinct effective connectivity pattern for this group. Therefore, the present research, for the first time, reveals that the activation of and the functional connectivity between Broca's area and the left STG play a critical role in the ability of the rule-based use of the WCI which is crucial for complex hierarchical structure building, and might be substantially corresponding to the "labeling competence" within the linguistic framework.

Neural correlates of semantic and phonological processing revealed by functional connectivity patterns in the language network

Semantics and phonology are fundamental components of language. Neuroimaging studies have identified a language network (LN) that is distributed through multiple regions and exhibits preferential responses to semantic and phonological information. However, it is unclear how these regions work collaboratively to support the processing of these components. In the present study, we first defined the LN as voxels that responded more to sentences than to strings of Chinese pseudo-characters. We subsequently used a voxel-based global brain connectivity method based on resting-state functional connectivity (FC) to characterize the neural correlates of semantic and phonological processing. We specifically correlated the within-network connectivity (WNC) of each voxel in the LN with the participants' scores on the semantic and phonological components extracted from a battery of reading tests via principal component analysis. We found that individuals with stronger WNC in the left posterior superior temporal gyrus (lpSTG) and anterior superior temporal gyrus (laSTG) were better at semantic and phonological processing, respectively. Furthermore, the FC of the lpSTG with the laSTG and bilateral fusiform gyrus mainly contributed to semantic processing, whereas the FC of the laSTG with the left posterior middle temporal gyrus and inferior frontal gyrus largely contributed to phonological processing. Importantly, the semantic and phonological subnetworks overlapped in the laSTG, the WNC of which correlated with the participants' performances during semantic-phonological interactions. Our study revealed the hub and subnetwork for semantic and phonological processing, respectively, and highlighted the role of the laSTG in semantic-phonological interactions.

Distinct sensitivities of the lateral prefrontal cortex and extrastriate body area to contingency between executed and observed actions

Detecting relationships between our own actions and the subsequent actions of others is critical for our social behavior. Self-actions differ from those of others in terms of action kinematics, body identity, and feedback timing. Thus, the detection of social contingency between self-actions and those of others requires comparison and integration of these three dimensions. Neuroimaging studies have highlighted the role of the frontotemporal network in action representation, but the role of each node and their relationships are still controversial. Here, we conducted a functional MRI experiment to test the hypothesis that the lateral prefrontal cortex and lateral occipito-temporal cortex are critical for the integration processes for social contingency. Twenty-four adults performed right finger gestures and then observed them as feedback. We manipulated three parameters of visual feedback: action kinematics (same or different gestures), body identity (self or other), and feedback timing (simultaneous or delayed). Three-way interactions of these factors were observed in the left inferior and middle frontal gyrus (IFG/MFG). These areas were active when self-actions were directly fed back in real-time (i.e., the condition causing a sense of agency), and when participants observed gestures performed by others after a short delay (i.e., the condition causing social contingency). In contrast, the left extrastriate body area (EBA) was sensitive to the concordance of action kinematics regardless of body identity or feedback timing. Body identity × feedback timing interactions were observed in regions including the superior parietal lobule (SPL). An effective connectivity analysis supported the model wherein experimental parameters modulated connections from the occipital cortex to the IFG/MFG via the EBA and SPL. These results suggest that both social contingency and the sense of agency are achieved by hierarchical processing that begins with simple concordance coding in the left EBA, leading to the complex coding of social relevance in the left IFG/MFG.

Connectivity profiles of the insular network for speech control in healthy individuals and patients with spasmodic dysphonia

The importance of insula in speech control is acknowledged but poorly understood, partly due to a variety of clinical symptoms resulting from insults to this structure. To clarify its structural organization within the speech network in healthy subjects, we used probabilistic diffusion tractography to examine insular connectivity with three cortical regions responsible for sound processing [Brodmann area (BA) 22], motor preparation (BA 44) and motor execution (laryngeal/orofacial primary motor cortex, BA 4). To assess insular reorganization in a speech disorder, we examined its structural connectivity in patients with spasmodic dysphonia (SD), a neurological condition that selectively affects speech production. We demonstrated structural segregation of insula into three non-overlapping regions, which receive distinct connections from BA 44 (anterior insula), BA 4 (mid-insula) and BA 22 (dorsal and posterior insula). There were no significant differences either in the number of streamlines connecting each insular subdivision to the cortical target or hemispheric lateralization of insular clusters and their projections between healthy subjects and SD patients. However, spatial distribution of the insular subdivisions connected to BA 4 and BA 44 was distinctly organized in healthy controls and SD patients, extending ventro-posteriorly in the former group and anterio-dorsally in the latter group. Our findings point to structural segregation of the insular sub-regions, which may be associated with the different aspects of sensorimotor and cognitive control of speech production. We suggest that distinct insular involvement may lead to different clinical manifestations when one or the other insular region and/or its connections undergo spatial reorganization.

Predictive Brain Mechanisms in Sound-to-Meaning Mapping during Speech Processing

Spoken language comprehension relies not only on the identification of individual words, but also on the expectations arising from contextual information. A distributed frontotemporal network is known to facilitate the mapping of speech sounds onto their corresponding meanings. However, how prior expectations influence this efficient mapping at the neuroanatomical level, especially in terms of individual words, remains unclear. Using fMRI, we addressed this question in the framework of the dual-stream model by scanning native speakers of Mandarin Chinese, a language highly dependent on context. We found that, within the ventral pathway, the violated expectations elicited stronger activations in the left anterior superior temporal gyrus and the ventral inferior frontal gyrus (IFG) for the phonological-semantic prediction of spoken words. Functional connectivity analysis showed that expectations were mediated by both top-down modulation from the left ventral IFG to the anterior temporal regions and enhanced cross-stream integration through strengthened connections between different subregions of the left IFG. By further investigating the dynamic causality within the dual-stream model, we elucidated how the human brain accomplishes sound-to-meaning mapping for words in a predictive manner.

SIGNIFICANCE STATEMENT

In daily communication via spoken language, one of the core processes is understanding the words being used. Effortless and efficient information exchange via speech relies not only on the identification of individual spoken words, but also on the contextual information giving rise to expected meanings. Despite the accumulating evidence for the bottom-up perception of auditory input, it is still not fully understood how the top-down modulation is achieved in the extensive frontotemporal cortical network. Here, we provide a comprehensive description of the neural substrates underlying sound-to-meaning mapping and demonstrate how the dual-stream model functions in the modulation of expectations, allowing for a better understanding of how the human brain accomplishes sound-to-meaning mapping in a predictive manner.

Effective Connectivity between Ventral Occipito-Temporal and Ventral Inferior Frontal Cortex during Lexico-Semantic Processing. A Dynamic Causal Modeling Study

It has been suggested that dorsal and ventral pathways support distinct aspects of language processing. Yet, the full extent of their involvement and their inter-regional connectivity in visual word recognition is still unknown. Studies suggest that they might reflect the dual-route model of reading, with the dorsal pathway more involved in grapho-phonological conversion during phonological tasks, and the ventral pathway performing lexico-semantic access during semantic tasks. Furthermore, this subdivision is also suggested at the level of the inferior frontal cortex, involving ventral and dorsal parts for lexico-semantic and phonological processing, respectively. In the present study, we assessed inter-regional brain connectivity and task-induced modulations of brain activity during a phoneme detection and semantic categorization tasks, using fMRI in healthy subject. We used a dynamic causal modeling approach to assess inter-regional connectivity and task demand modulation within the dorsal and ventral pathways, including the following network components: the ventral occipito-temporal cortex (vOTC; dorsal and ventral), the superior temporal gyrus (STG; dorsal), the dorsal inferior frontal gyrus (dIFG; dorsal), and the ventral IFG (vIFG; ventral). We report three distinct inter-regional interactions supporting orthographic information transfer from vOTC to other language regions (vOTC -> STG, vOTC -> vIFG and vOTC -> dIFG) regardless of task demands. Moreover, we found that (a) during semantic processing (direct ventral pathway) the vOTC -> vIFG connection strength specifically increased and (b) a lack of modulation of the vOTC -> dIFG connection strength by the task that could suggest a more general involvement of the dorsal pathway during visual word recognition. Results are discussed in terms of anatomo-functional connectivity of visual word recognition network.

Possible roles for fronto-striatal circuits in reading disorder

Several studies have reported hyperactivation in frontal and striatal regions in individuals with reading disorder (RD) during reading-related tasks. Hyperactivation in these regions is typically interpreted as a form of neural compensation related to articulatory processing. Fronto-striatal hyperactivation in RD could however, also arise from fundamental impairment in reading related processes, such as phonological processing and implicit sequence learning relevant to early language acquisition. We review current evidence for the compensation hypothesis in RD and apply large-scale reverse inference to investigate anatomical overlap between hyperactivation regions and neural systems for articulation, phonological processing, implicit sequence learning. We found anatomical convergence between hyperactivation regions and regions supporting articulation, consistent with the proposed compensatory role of these regions, and low convergence with phonological and implicit sequence learning regions. Although the application of large-scale reverse inference to decode function in a clinical population should be interpreted cautiously, our findings suggest future lines of research that may clarify the functional significance of hyperactivation in RD.

Possible roles for fronto-striatal circuits in reading disorder

Several studies have reported hyperactivation in frontal and striatal regions in individuals with reading disorder (RD) during reading-related tasks. Hyperactivation in these regions is typically interpreted as a form of neural compensation related to articulatory processing. Fronto-striatal hyperactivation in RD could however, also arise from fundamental impairment in reading related processes, such as phonological processing and implicit sequence learning relevant to early language acquisition. We review current evidence for the compensation hypothesis in RD and apply large-scale reverse inference to investigate anatomical overlap between hyperactivation regions and neural systems for articulation, phonological processing, implicit sequence learning. We found anatomical convergence between hyperactivation regions and regions supporting articulation, consistent with the proposed compensatory role of these regions, and low convergence with phonological and implicit sequence learning regions. Although the application of large-scale reverse inference to decode function in a clinical population should be interpreted cautiously, our findings suggest future lines of research that may clarify the functional significance of hyperactivation in RD.

The Brain Effective Connectivity of Chinese during Rhyming Task

With regard to brain language processing, the activation patterns have been well studied, and recently there are great interest in the connectivity models. The crucial brain areas for phonological processing involves left inferior frontal gyrus (LIFG), left inferior parietal lobule (LIPL) and left posterior middle temporal gyrus (LpMTG). Specially in Chinese processing, the left middle frontal gyrus (LMFG) is considered as an essential region. However, the connectivity pattern among these brain areas is not well understood. In this study, a rhyming experiment of Chinese was conducted, and the Dynamic causal modeling (DCM) and the Bayesian model selection (BMS) were used to examine the interaction between brain regions and choose the best model for rhyming task of Chinese. By examining the interactions, it was found that LMFG exerted inhibitory modulation on LIPL and LIFG; the phonological processing enhanced the connection from LIPL to LIFG and LMFG, which suggested the important roles of these connections for the increased phonological load; And LpMTG modulated LIFG and LMFG negatively, and LIPL positively under rhyming judgment task.

Asymmetric intra- and interhemispheric interactions during covert and overt sentence reading

Covert and overt sentence reading evoke lateralized activations in overall bihemispheric networks. We assumed that the study of functional connectivity may reveal underlying principles of functional lateralization. Left-lateralized activations could relate to stronger reading-related modulation of intrahemispheric functional connectivity in the left than the right hemisphere. Alternatively, left-lateralization could result from suppression of contralateral processing and thus reflect asymmetric interhemispheric interactions. To address this issue, this functional MRI study investigated the regional lateralization of covert and overt German sentence reading in 39 healthy participants. Further, it revealed the modulation of the lateralized brain regions' functional connectivity and their contralateral homotopes by covert and overt reading (psychophysiological interactions). Left-lateralization during covert reading was associated with stronger intrahemispheric coupling particularly in the left dorsal stream rather than with suppression of contralateral processing. Lateralization during overt sentence reading instead went along with additional recruitment of right perisylvian cortices involved in articulation by asymmetric positive heterotopic interhemispheric interactions. Given the paucity of interhemispheric anti-correlations with homotopic regions, functional lateralization is likely a consequence of a task-dependent interplay between asymmetric positive intra- and interhemispheric coupling.

The Relationship between Frontotemporal Effective Connectivity during Picture Naming, Behavior, and Preserved Cortical Tissue in Chronic Aphasia

While several studies of task-based effective connectivity of normal language processing exist, little is known about the functional reorganization of language networks in patients with stroke-induced chronic aphasia. During oral picture naming, activation in neurologically intact individuals is found in "classic" language regions involved with retrieval of lexical concepts [e.g., left middle temporal gyrus (LMTG)], word form encoding [e.g., left posterior superior temporal gyrus, (LpSTG)], and controlled retrieval of semantic and phonological information [e.g., left inferior frontal gyrus (LIFG)] as well as domain-general regions within the multiple demands network [e.g., left middle frontal gyrus (LMFG)]. After stroke, lesions to specific parts of the left hemisphere language network force reorganization of this system. While individuals with aphasia have been found to recruit similar regions for language tasks as healthy controls, the relationship between the dynamic functioning of the language network and individual differences in underlying neural structure and behavioral performance is still unknown. Therefore, in the present study, we used dynamic causal modeling (DCM) to investigate differences between individuals with aphasia and healthy controls in terms of task-induced regional interactions between three regions (i.e., LIFG, LMFG, and LMTG) vital for picture naming. The DCM model space was organized according to exogenous input to these regions and partitioned into separate families. At the model level, random effects family wise Bayesian Model Selection revealed that models with driving input to LIFG best fit the control data whereas models with driving input to LMFG best fit the patient data. At the parameter level, a significant between-group difference in the connection strength from LMTG to LIFG was seen. Within the patient group, several significant relationships between network connectivity parameters, spared cortical tissue, and behavior were observed. Overall, this study provides some preliminary findings regarding how neural networks for language reorganize for individuals with aphasia and how brain connectivity relates to underlying structural integrity and task performance.

From perceptual to lexico-semantic analysis--cortical plasticity enabling new levels of processing

Certain kinds of stimuli can be processed on multiple levels. While the neural correlates of different levels of processing (LOPs) have been investigated to some extent, most of the studies involve skills and/or knowledge already present when performing the task. In this study we specifically sought to identify neural correlates of an evolving skill that allows the transition from perceptual to a lexico-semantic stimulus analysis. Eighteen participants were trained to decode 12 letters of Morse code that were presented acoustically inside and outside of the scanner environment. Morse code was presented in trains of three letters while brain activity was assessed with fMRI. Participants either attended to the stimulus length (perceptual analysis), or evaluated its meaning distinguishing words from nonwords (lexico-semantic analysis). Perceptual and lexico-semantic analyses shared a mutual network comprising the left premotor cortex, the supplementary motor area (SMA) and the inferior parietal lobule (IPL). Perceptual analysis was associated with a strong brain activation in the SMA and the superior temporal gyrus bilaterally (STG), which remained unaltered from pre and post training. In the lexico-semantic analysis post learning, study participants showed additional activation in the left inferior frontal cortex (IFC) and in the left occipitotemporal cortex (OTC), regions known to be critically involved in lexical processing. Our data provide evidence for cortical plasticity evolving with a learning process enabling the transition from perceptual to lexico-semantic stimulus analysis. Importantly, the activation pattern remains task-related LOP and is thus the result of a decision process as to which LOP to engage in.

Time-varying effective connectivity during visual object naming as a function of semantic demands

Accumulating evidence suggests that visual object understanding involves a rapid feedforward sweep, after which subsequent recurrent interactions are necessary. The extent to which recurrence plays a critical role in object processing remains to be determined. Recent studies have demonstrated that recurrent processing is modulated by increasing semantic demands. Differentially from previous studies, we used dynamic causal modeling to model neural activity recorded with magnetoencephalography while 14 healthy humans named two sets of visual objects that differed in the degree of semantic accessing demands, operationalized in terms of the values of basic psycholinguistic variables associated with the presented objects (age of acquisition, frequency, and familiarity). This approach allowed us to estimate the directionality of the causal interactions among brain regions and their associated connectivity strengths. Furthermore, to understand the dynamic nature of connectivity (i.e., the chronnectome; Calhoun et al., 2014) we explored the time-dependent changes of effective connectivity during a period (200-400 ms) where adding semantic-feature information improves modeling and classifying visual objects, at 50 ms increments. First, we observed a graded involvement of backward connections, that became active beyond 200 ms. Second, we found that semantic demands caused a suppressive effect in the backward connection from inferior frontal cortex (IFC) to occipitotemporal cortex over time. These results complement those from previous studies underscoring the role of IFC as a common source of top-down modulation, which drives recurrent interactions with more posterior regions during visual object recognition. Crucially, our study revealed the inhibitory modulation of this interaction in situations that place greater demands on the conceptual system.

Broca's area network in language function: a pooling-data connectivity study

Background and Objective: Modern neuroimaging developments have demonstrated that cognitive functions correlate with brain networks rather than specific areas. The purpose of this paper was to analyze the connectivity of Broca’s area based on language tasks.

Methods: A connectivity modeling study was performed by pooling data of Broca’s activation in language tasks. Fifty-seven papers that included 883 subjects in 84 experiments were analyzed. Analysis of Likelihood Estimates of pooled data was utilized to generate the map; thresholds at p < 0.01 were corrected for multiple comparisons and false discovery rate. Resulting images were co-registered into MNI standard space.

Results: A network consisting of 16 clusters of activation was obtained. Main clusters were located in the frontal operculum, left posterior temporal region, supplementary motor area, and the parietal lobe. Less common clusters were seen in the sub-cortical structures including the left thalamus, left putamen, secondary visual areas, and the right cerebellum.

Conclusion: Broca’s area-44-related networks involved in language processing were demonstrated utilizing a pooling-data connectivity study. Significance, interpretation, and limitations of the results are discussed.

Alpha phase determines successful lexical decision in noise

Psychophysical target detection has been shown to be modulated by slow oscillatory brain phase. However, thus far, only low-level sensory stimuli have been used as targets. The current human electroencephalography (EEG) study examined the influence of neural oscillatory phase on a lexical-decision task performed for stimuli embedded in noise. Neural phase angles were compared for correct versus incorrect lexical decisions using a phase bifurcation index (BI), which quantifies differences in mean phase angles and phase concentrations between correct and incorrect trials. Neural phase angles in the alpha frequency range (8-12 Hz) over right anterior sensors were approximately antiphase in a prestimulus time window, and thus successfully distinguished between correct and incorrect lexical decisions. Moreover, alpha-band oscillations were again approximately antiphase across participants for correct versus incorrect trials during a later peristimulus time window (∼500 ms) at left-central electrodes. Strikingly, lexical decision accuracy was not predicted by either event-related potentials (ERPs) or oscillatory power measures. We suggest that correct lexical decisions depend both on successful sensory processing, which is made possible by the alignment of stimulus onset with an optimal alpha phase, as well as integration and weighting of decisional information, which is coupled to alpha phase immediately following the critical manipulation that differentiated words from pseudowords. The current study constitutes a first step toward characterizing the role of dynamic oscillatory brain states for higher cognitive functions, such as spoken word recognition.

The neural bases of the pseudohomophone effect: Phonological constraints on lexico-semantic access in reading

We investigated phonological processing in normal readers to answer the question to what extent phonological recoding is active during silent reading and if or how it guides lexico-semantic access. We addressed this issue by looking at pseudohomophone and baseword frequency effects in lexical decisions with event-related functional magnetic resonance imaging (fMRI). The results revealed greater activation in response to pseudohomophones than for well-controlled pseudowords in the left inferior/superior frontal and middle temporal cortex, left insula, and left superior parietal lobule. Furthermore, we observed a baseword frequency effect for pseudohomophones (e.g., FEAL) but not for pseudowords (e.g., FEEP). This baseword frequency effect was qualified by activation differences in bilateral angular and left supramarginal, and bilateral middle temporal gyri for pseudohomophones with low- compared to high-frequency basewords. We propose that lexical decisions to pseudohomophones involves phonology-driven lexico-semantic activation of their basewords and that this is converging neuroimaging evidence for automatically activated phonological representations during silent reading in experienced readers.

Cross-language differences in the brain network subserving intelligible speech

How is language processed in the brain by native speakers of different languages? Is there one brain system for all languages or are different languages subserved by different brain systems? The first view emphasizes commonality, whereas the second emphasizes specificity. We investigated the cortical dynamics involved in processing two very diverse languages: a tonal language (Chinese) and a nontonal language (English). We used functional MRI and dynamic causal modeling analysis to compute and compare brain network models exhaustively with all possible connections among nodes of language regions in temporal and frontal cortex and found that the information flow from the posterior to anterior portions of the temporal cortex was commonly shared by Chinese and English speakers during speech comprehension, whereas the inferior frontal gyrus received neural signals from the left posterior portion of the temporal cortex in English speakers and from the bilateral anterior portion of the temporal cortex in Chinese speakers. Our results revealed that, although speech processing is largely carried out in the common left hemisphere classical language areas (Broca's and Wernicke's areas) and anterior temporal cortex, speech comprehension across different language groups depends on how these brain regions interact with each other. Moreover, the right anterior temporal cortex, which is crucial for tone processing, is equally important as its left homolog, the left anterior temporal cortex, in modulating the cortical dynamics in tone language comprehension. The current study pinpoints the importance of the bilateral anterior temporal cortex in language comprehension that is downplayed or even ignored by popular contemporary models of speech comprehension.

Social discounting involves modulation of neural value signals by temporoparietal junction

Most people are generous, but not toward everyone alike: generosity usually declines with social distance between individuals, a phenomenon called social discounting. Despite the pervasiveness of social discounting, social distance between actors has been surprisingly neglected in economic theory and neuroscientific research. We used functional magnetic resonance imaging (fMRI) to study the neural basis of this process to understand the neural underpinnings of social decision making. Participants chose between selfish and generous alternatives, yielding either a large reward for the participant alone, or smaller rewards for the participant and another individual at a particular social distance. We found that generous choices engaged the temporoparietal junction (TPJ). In particular, the TPJ activity was scaled to the social-distance-dependent conflict between selfish and generous motives during prosocial choice, consistent with ideas that the TPJ promotes generosity by facilitating overcoming egoism bias. Based on functional coupling data, we propose and provide evidence for a biologically plausible neural model according to which the TPJ supports social discounting by modulating basic neural value signals in the ventromedial prefrontal cortex to incorporate social-distance-dependent other-regarding preferences into an otherwise exclusively own-reward value representation.

Left middle temporal and inferior frontal regions contribute to speed of lexical decision: a TMS study

Activation of left anterior inferior frontal gyrus (aLIFG) and left middle temporal gyrus (LMTG) has been observed in some functional neuroimaging studies of lexical decision but not others. It is thus unclear whether these two regions are necessary for word recognition. By applying continuous theta-burst transcranial magnetic stimulation (TMS) which temporally suppresses local brain function, we examined whether aLIFG and LMTG play causal roles in word recognition in a visual lexical decision task (LDT). Furthermore, we manipulated stimulus onset asynchrony (SOA) between prime and target to test whether these regions contribute to word recognition differently. In the LDT task, target words were preceded by semantically related primes (Related Condition; RC) or semantically unrelated words (Unrelated Condition; UC), under both short (150 ms) and long (600 ms) SOA conditions. TMS of aLIFG and LMTG significantly affected the word recognition speed compared to TMS of Vertex. Our results provide evidence that both aLIFG and LMTG contribute to word recognition speed. Furthermore, at short SOA, TMS of aLIFG or LMTG prolonged reaction time (RT). In contrast, at long SOA, there was a significant region by SOA by TMS interaction such that TMS of aLIFG prolonged RT, whereas TMS of LMTG speeded RT. These results suggest that aLIFG and LMTG may play different roles in word recognition.

Effective connectivity of the posterior cingulate and medial prefrontal cortices relates to working memory impairment in schizophrenic and bipolar patients

BACKGROUND

Schizophrenia (SZ) and bipolar I disorder (BD) share many overlapping clinical features, confounding the current diagnostic systems. Recent studies suggest the posterior cingulate (PCC) and medial prefrontal (MPFC) cortices that are involved in SZ and BD pathophysiology. However, the roles of PCC and MPFC in providing specific distinctive and shared neural substrates between these two disorders remain largely unknown. Examining the neurophysiologic mechanism of these diseases may help explain the clinical observations and differentiate the two disorders.

METHODS

We used the Dynamic Casual Modeling (DCM), which is capable of eliciting hidden neuronal dynamics and reveal cross-regulation of multiple neuronal systems, to characterize the pattern of disrupted effective connectivity in the left PCC-MPFC circuit during working memory tasks in 36 SZ and 20 BD patients as well as 29 healthy controls.

RESULTS

Compared to the healthy controls, both SZ and BD patient groups exhibited significant negative effective connectivity from the left MPFC to PCC. The negative effective connectivity was more remarkable in schizophrenic patients. Only patients with BD differed from healthy controls with positive effective connectivity from the left PCC to MPFC.

CONCLUSIONS

Whole brain analysis revealed deactivation of the left PCC and MPFC across all patient groups. This study provides new insight that changes in effective connectivity of the left MPFC to left PCC circuit during working memory processing may be a core pathophysiological feature distinguishing SZ from BD.

Common molecular basis of the sentence comprehension network revealed by neurotransmitter receptor fingerprints

The language network is a well-defined large-scale neural network of anatomically and functionally interacting cortical areas. The successful language process requires the transmission of information between these areas. Since neurotransmitter receptors are key molecules of information processing, we hypothesized that cortical areas which are part of the same functional language network may show highly similar multireceptor expression pattern ("receptor fingerprint"), whereas those that are not part of this network should have different fingerprints. Here we demonstrate that the relation between the densities of 15 different excitatory, inhibitory and modulatory receptors in eight language-related areas are highly similar and differ considerably from those of 18 other brain regions not directly involved in language processing. Thus, the fingerprints of all cortical areas underlying a large-scale cognitive domain such as language is a characteristic, functionally relevant feature of this network and an important prerequisite for the underlying neuronal processes of language functions.

Shared vs. specific brain activation changes in dyslexia after training of phonology, attention, or reading

Whereas the neurobiological basis of developmental dyslexia has received substantial attention, only little is known about the processes in the brain during remediation. This holds in particular in light of recent findings on cognitive subtypes of dyslexia which suggest interactions between individual profiles, training methods, and also the task in the scanner. Therefore, we trained three groups of German dyslexic primary school children in the domains of phonology, attention, or visual word recognition. We compared neurofunctional changes after 4 weeks of training in these groups to those in untrained normal readers in a reading task and in a task of visual attention. The overall reading improvement in the dyslexic children was comparable over groups. It was accompanied by substantial increase of the activation level in the visual word form area (VWFA) during a reading task inside the scanner. Moreover, there were activation increases that were unique for each training group in the reading task. In contrast, when children performed the visual attention task, shared training effects were found in the left inferior frontal sulcus and gyrus, which varied in amplitude between the groups. Overall, the data reveal that different remediation programmes matched to individual profiles of dyslexia may improve reading ability and commonly affect the VWFA in dyslexia as a shared part of otherwise distinct networks.