Chiao-Yi Wu

A meta-analysis of fMRI studies on Chinese orthographic, phonological, and semantic processing

A growing body of neuroimaging evidence has shown that Chinese character processing recruits differential activation from alphabetic languages due to its unique linguistic features. As more investigations on Chinese character processing have recently become available, we applied a meta-analytic approach to summarize previous findings and examined the neural networks for orthographic, phonological, and semantic processing of Chinese characters independently. The activation likelihood estimation (ALE) method was used to analyze eight studies in the orthographic task category, eleven in the phonological and fifteen in the semantic task categories. Converging activation among three language-processing components was found in the left middle frontal gyrus, the left superior parietal lobule and the left mid-fusiform gyrus, suggesting a common sub-network underlying the character recognition process regardless of the task nature. With increasing task demands, the left inferior parietal lobule and the right superior temporal gyrus were specialized for phonological processing, while the left middle temporal gyrus was involved in semantic processing. Functional dissociation was identified in the left inferior frontal gyrus, with the posterior dorsal part for phonological processing and the anterior ventral part for semantic processing. Moreover, bilateral involvement of the ventral occipito-temporal regions was found for both phonological and semantic processing. The results provide better understanding of the neural networks underlying Chinese orthographic, phonological, and semantic processing, and consolidate the findings of additional recruitment of the left middle frontal gyrus and the right fusiform gyrus for Chinese character processing as compared with the universal language network that has been based on alphabetic languages.

Biofunctionalized magnetic nanoparticles for in vitro labeling and in vivo locating specific biomolecules

In this work, we developed processes to biofunctionalize magnetic nanoparticles dispersed in phosphate buffer saline solution. For future clinical utility, magnetic nanoparticles were biofunctionalized with anti-vascular cell adhesion molecule-1 (VCAM-1) to label the VCAM-1 molecule, which served as an indicator for the lesions prone to vulnerable atherosclerotic plaque formation. The biofunctionalized magnetic nanoparticles were used to magnetically label, in vitro, cells expressing VCAM-1, as well as to locate the vulnerable aortic lesions of hypercholesterolemic rabbits with the aid of magnetic resonance imaging. In addition to demonstrating the feasibility of using biofunctionalized magnetic nanoparticles for biomolecule assays, the relevant physical mechanisms are discussed.

Neural substrates of phonological selection for Japanese character Kanji based on fMRI investigations

Japanese and Chinese both share the same ideographic/logographic character system. How these characters are processed, however, is inherently different for each language. We harnessed the unique property of homophone judgment in Japanese kanji to provide an analogous Chinese condition using event-related functional magnetic resonance imaging (fMRI) in 33 native Japanese speakers. We compared two types of kanji: (1) kanji that usually evokes only one pronunciation to Japanese speakers, which is representative of most Chinese characters (monophonic character); (2) kanji that evoked multiple pronunciation candidates, which is typical in Japanese kanji (heterophonic character). Results showed that character pairs with multiple sound possibilities increased activation in posterior regions of the left, middle and inferior frontal gyri (MFG and IFG), the bilateral anterior insulae, and the left anterior cingulate cortex as compared with those of kanji with only one sound. The activity seen in the MFG, dorsal IFG, and ventral IFG in the left posterior lateral prefrontal cortex, which was thought to correspond with language components of orthography, phonology, and semantics, respectively, was discussed in regards to their potentially important roles in information selection among competing sources of the components. A comparison with previous studies suggested that detailed analyses of activation in these language areas could explain differences between Japanese and Chinese, such as a greater involvement of the prefrontal language production regions for Japanese, whereas, for Chinese there is more phonological processing of inputs in the superior temporal gyrus.

Age-related differences in effective connectivity of brain regions involved in Japanese kanji processing with homophone judgment task.

Reading is a complex process involving neural networks in which connections may be influenced by task demands and other factors. We employed functional magnetic resonance imaging and dynamic causal modeling to examine age-related influences on left-hemispheric kanji reading networks. During a homophone judgment task, activation in the middle frontal gyrus, and dorsal and ventral inferior frontal gyri were identified, representing areas involved in orthographic, phonological, and semantic processing, respectively. The young adults showed a preference for a semantically-mediated pathway from orthographic inputs to the retrieval of phonological representations, whereas the elderly preferred a direct connection from orthographic inputs to phonological lexicons prior to the activation of semantic representations. These sequential pathways are in line with the lexical semantic and non-semantic routes in the dual-route cascaded model. The shift in reading pathways accompanied by slowed reaction time for the elderly might suggest age-related declines in the efficiency of network connectivity.

Age-related changes in resting-state and task-activated functional MRI networks

Resting-State Networks (RSNs) shown in functional magnetic resonance imaging (fMRI) have been consistently and reliably identified. Amongst these, the Default Mode Network (DMN) has been most well researched and shown to have age-related decrease in functional connectivity and negative consequences for cognition. There are two other distinct RSNs, Salience Network (SN) and Executive Control Network (ECN), shown to co-activate during fMRI tasks. The SN has been suggested to be correlated with cognitive decline in healthy aging, however, the age-related dynamics between these three RSNs are not well understood. The current study examined the DMN, SN and ECN during resting-state fMRI in young and elderly from Japan and Singapore using data-driven independent component analysis (ICA) and functional network connectivity (FNC). We further investigated if the functional connectivity of the DMN and SN varied across tasks of different cognitive demands between young and elderly. Interestingly, the elderly had increased intrinsic activity that deviated from the expected DMN, SN and ECN, and increased functional connectivity within the anterior SN relative to the young during resting-state fMRI. For task fMRI, the elderly showed decreased activation in the primary networks of visual and motor processing, and increased task related activity for higher cognitive processes. However, the DMN and SN for task fMRI revealed consistent increased activity shifted outside the expected regions for the elderly. Difference in functional connectivity between young and elderly was varied across tasks. The elderly had marginally less number of correlated component pairs compared to the young, suggesting a decline in functional network integrity in aging. The current study demonstrated that resting-state data could be combined across two sites using ICA, as well as the use of DMN and SN as reliable networks to examine age-related changes in rest and task fMRI. Understanding the dynamics of these networks in relation to aging will provide potential neuroimaging markers for enhancing cognition, as well as detecting pathological decline.

Extensive stimulus repetition leads older adults to show delayed functional magnetic resonance imaging adaptation

We investigated whether extensive repetition can diminish age-related differences between younger and older adults in functional magnetic resonance adaptation (fMR-A). Datasets were obtained from 26 younger and 24 older healthy adults presented with two scenes that repeated 20 times amongst other novel scenes during fMRI scanning. The average cortical responses to the first eight (Repetitions 1-7) and the last eight (Repetitions 12-19) presentations out of 20 were compared within each group. Younger adults showed similar levels of fMR-A in both repetition sets. Conversely, older adults did not show reliable fMR-A in Repetitions 1-7, but they did in Repetitions 12-19; subtracting the latter from the former revealed a significant effect within left inferior occipital, left lingual, and the posterior part of fusiform gyrus. We concluded that cortical responsiveness in older adults are compromised, but extensive repetition can lead older adults to show a delayed but closer level of fMR-A compared to younger adults.

The role of regional heterogeneity in age-related differences in functional hemispheric asymmetry: an fMRI study

ABSTRACT Neuroimaging literature has documented age-related hemispheric asymmetry reduction in frontal regions during task performances. As most studies employed working memory paradigms, it is therefore less clear if this pattern of neural reorganization is constrained by working memory processes or it would also emerge in other cognitive domains which are predominantly lateralized. Using blocked functional magnetic resonance imaging (fMRI), the present study used a homophone judgment task and a line judgment task to investigate age-related differences in functional hemispheric asymmetry in language and visuospatial processing respectively. Young and older adults achieved similar task accuracy although older adults required a significantly longer time. Age-related functional hemispheric asymmetry reduction was found only in dorsal inferior frontal gyrus and was associated with better performance when the homophone condition was contrasted against fixation, and not line condition. Our data thus highlights the importance of considering regional heterogeneity of aging effects together with general age-related cognitive processes.