Danling Peng

Use of fNIRS to assess resting state functional connectivity

Recently, resting state functional connectivity (RSFC) studies based on fMRI and EEG/MEG have provided valuable insight into the intrinsic functional architecture of the human brain. However, whether functional near infrared spectroscopy (fNIRS), a suitable imaging method for infant and patient populations, can be used to examine RSFC remains elusive. Using an ETG-4000 Optical Topography System, the present study measured 29 adult subjects (14 females) over the sensorimotor and auditory cortexes during a resting session and a motor-localizer task session. The RSFC maps were computed by seed-based correlation analysis and data-driven cluster analysis. The results from both analyses showed robust RSFC maps, which were not only consistent with the localizer task-related activation results, but also those of previous fMRI findings. Moreover, the strong consistency between the seed-based correlation analysis and the data-driven cluster analysis further validated the use of fNIRS to assess RSFC. The potential influence of a specific low-frequency filtering range (0.04-0.15 Hz and 0.01-0.08 Hz) and three fNIRS parameters (oxy-Hb, deoxy-Hb, and total-Hb) on RSFC results were also examined.

Neural Synchronization during Face-to-Face Communication

Although the human brain may have evolutionarily adapted to face-to-face communication, other modes of communication, e.g., telephone and e-mail, increasingly dominate our modern daily life. This study examined the neural difference between face-to-face communication and other types of communication by simultaneously measuring two brains using a hyperscanning approach. The results showed a significant increase in the neural synchronization in the left inferior frontal cortex during a face-to-face dialog between partners but none during a back-to-back dialog, a face-to-face monologue, or a back-to-back monologue. Moreover, the neural synchronization between partners during the face-to-face dialog resulted primarily from the direct interactions between the partners, including multimodal sensory information integration and turn-taking behavior. The communicating behavior during the face-to-face dialog could be predicted accurately based on the neural synchronization level. These results suggest that face-to-face communication, particularly dialog, has special neural features that other types of communication do not have and that the neural synchronization between partners may underlie successful face-to-face communication.

Specialization of phonological and semantic processing in Chinese word reading

The purpose of this study was to examine the neurocognitive network for processing visual word forms in native Chinese speakers using functional magnetic resonance imaging (fMRI). In order to compare the processing of phonological and semantic representations, we developed parallel rhyming and meaning association judgment tasks that required explicit access and manipulation of these representations. Subjects showed activation in left inferior/middle frontal gyri, bilateral medial frontal gyri, bilateral middle occipital/fusiform gyri, and bilateral cerebella for both the rhyming and meaning tasks. A direct comparison of the tasks revealed that the rhyming task showed more activation in the posterior dorsal region of the inferior/middle frontal gyrus (BA 9/44) and in the inferior parietal lobule (BA 40). The meaning task showed more activation in the anterior ventral region of the inferior/middle frontal gyrus (BA 47) and in the superior/middle temporal gyrus (BA 22,21). These findings are consistent with previous studies in English that suggest specialization of inferior frontal regions for the access and manipulation of phonological vs. semantic representations, but also suggest that this specialization extends to the middle frontal gyrus for Chinese. These findings are also consistent with the suggestion that the left middle temporal gyrus is involved in representing semantic information and the left inferior parietal lobule is involved in mapping between orthographic and phonological representations.

Altered effective connectivity and anomalous anatomy in the basal ganglia-thalamocortical circuit of stuttering speakers

Combining structural equation modeling (SEM) and voxel-based morphometry (VBM), this study investigated the interactions among neural structures in the basal ganglia-thalamocortical circuit (BGTC) in the left hemisphere of stuttering and non-stuttering speakers. Stuttering speakers (n=12) and non-stuttering controls (n=12) were scanned while performing a picture-naming task and a passive-viewing (baseline) task. Results showed significant differences between stuttering and non-stuttering speakers in both effective connectivity and anatomical structures in the BGTC in the left brain. Specifically, compared to non-stuttering speakers, stuttering speakers showed weaker negative connectivity from the left posterior middle temporal gyrus (PMTG) to the putamen, but stronger positive connectivity from the putamen to the thalamus, from the thalamus to the PMTG and anterior supplementary motor area (preSMA), and from the anterior superior temporal gyrus (ASTG) to the preSMA. Accompanying such altered connectivity were anatomical differences: compared to non-stuttering controls, stuttering speakers showed more grey matter (GM) volume concentration in the left putamen, less GM volume concentration in the left medial frontal gyrus and ASTG, and less white matter volume concentration underlying the left posterior superior temporal gyrus inside the BGTC. These results shed significant light on the neural mechanisms (in terms of both functional connectivity and neural anatomy) of stuttering.

Structural plasticity of the left caudate in bimodal bilinguals

Bilinguals need an effective neural mechanism to select and control their languages for successful communication. Recent evidence indicates that the left caudate nucleus (LCN) is a critical part of this mechanism. Here we show that bimodal bilinguals, who use spoken and sign languages, have greater grey matter volume (GMV) in the head of the LCN as compared to monolinguals. We also found higher functional activation of this region in bimodal bilinguals when they switched between sign language and spoken language compared to when they did not switch languages. Furthermore, GMV was positively correlated with the magnitude of the switching effect in the head of the LCN. These findings indicate that for bimodal bilinguals, the LCN is shaped by bilingualism both anatomically and functionally.

Developmental differences of neurocognitive networks for phonological and semantic processing in Chinese word reading.

Developmental differences in the neurocognitive networks for phonological and semantic processing in Chinese word reading were examined in 13 adults and 13 children using functional magnetic resonance imaging (fMRI). Rhyming and semantic association judgments were made to two‐character words that were presented sequentially in the visual modality. These lexical tasks were compared with a nonlinguistic control task involving judgment of line patterns. The first main finding was that adults showed greater activation than children in right middle occipital gyrus on both the meaning and rhyming task, suggesting adults more effectively engage right hemisphere brain regions involved in the visual‐spatial analysis of Chinese characters. The second main finding was that adults showed greater activation than children in left inferior parietal lobule for the rhyming as compared with the meaning task, suggesting greater specialization of phonological processing in adults. The third main finding was that children who had better performance in the rhyming task on characters with conflicting orthographic and phonological information relative to characters with nonconflicting information showed greater activation in left middle frontal gyrus, suggesting greater engagement of brain regions involved in the integration of orthography and phonology. Hum Brain Mapp, 2009.

Detecting resting-state functional connectivity in the language system using functional near-infrared spectroscopy

Functional connectivity has become one of the important approaches to understanding the functional organization of the human brain. Recently, functional near-infrared spectroscopy (fNIRS) was demonstrated as a feasible method to study resting-state functional connectivity (RSFC) in the sensory and motor systems. However, whether such fNIRS-based RSFC can be revealed in high-level and complex functional systems remains unknown. In the present study, the feasibility of such an approach is tested on the language system, of which the neural substrates have been well documented in the literature. After determination of a seed channel by a language localizer task, the correlation strength between the low frequency fluctuations of the fNIRS signal at the seed channel and those at all other channels is used to evaluate the language system RSFC. Our results show a significant RSFC between the left inferior frontal cortex and superior temporal cortex, components both associated with dominant language regions. Moreover, the RSFC map demonstrates left lateralization of the language system. In conclusion, the present study successfully utilized fNIRS-based RSFC to study a complex and high-level neural system, and provides further evidence for the validity of the fNIRS-based RSFC approach.

Speaking words in two languages with one brain: neural overlap and dissociation.

The present study investigated the neural overlap and dissociation underlying overt word production in the first language (L1) and second language (L2). Twenty-four Chinese-English bilinguals named pictures in either L1 or L2 while being scanned with functional magnetic resonance imaging (fMRI). When comparing picture naming in L2 to naming in L1, increased activity in the left inferior frontal gyrus, bilateral supplementary motor areas (SMA), left precentral gyrus, left lingual gyrus, left cuneus, bilateral putamen, bilateral globus pallidus, bilateral caudate and bilateral cerebellum were observed. This suggested that word production in L2 is less automatic and needs to recruit more neural resources for lexical retrieval, articulatory processing and cognitive control than in L1. In contrast, picture naming in L1 relative to picture naming in L2 revealed increased activity in the right putamen and right globus pallidus probably due to different phonological features between Chinese and English. In addition, the conjunction analysis, for the first time, revealed the common neural correlates underlying picture naming in L1 and L2.

Dissociation in the neural basis underlying Chinese tone and vowel production

Neuropsychologists have debated over whether the processing of segmental and suprasegmental units involves different neural mechanisms. Focusing on the production of Chinese lexical tones (suprasegmental units) and vowels (segmental units), this study used the adaptation paradigm to investigate a possible neural dissociation for tone and vowel production. Ten native Chinese speakers were asked to name Chinese characters and pinyin (Romanized phonetic system for Chinese language) that varied in terms of tones and vowels. fMRI results showed significant differences in the right inferior frontal gyrus between tone and vowel production (more activation for tones than for vowels). Brain asymmetry analysis further showed that tone production was less left-lateralized than vowel production, although both showed left-hemisphere dominance.

Second language experience modulates functional brain network for the native language production in bimodal bilinguals

The functional brain network of a bilinguals first language (L1) plays a crucial role in shaping that of his or her second language (L2). However, it is less clear how L2 acquisition changes the functional network of L1 processing in bilinguals. In this study, we demonstrate that in bimodal (Chinese spoken-sign) bilinguals, the functional network supporting L1 production (spoken language) has been reorganized to accommodate the network underlying L2 production (sign language). Using functional magnetic resonance imaging (fMRI) and a picture naming task, we find greater recruitment of the right supramarginal gyrus (RSMG), the right temporal gyrus (RSTG), and the right superior occipital gyrus (RSOG) for bilingual speakers versus monolingual speakers during L1 production. In addition, our second experiment reveals that these regions reflect either automatic activation of L2 (RSOG) or extra cognitive coordination (RSMG and RSTG) between both languages during L1 production. The functional connectivity between these regions, as well as between other regions that are L1- or L2-specific, is enhanced during L1 production in bimodal bilinguals as compared to their monolingual peers. These findings suggest that L1 production in bimodal bilinguals involves an interaction between L1 and L2, supporting the claim that learning a second language does, in fact, change the functional brain network of the first language.