Wai Ting Siok

Biological abnormality of impaired reading is constrained by culture.

Developmental dyslexia is characterized by a severe reading problem in people who have normal intelligence and schooling. Impaired reading of alphabetic scripts is associated with dysfunction of left temporoparietal brain regions. These regions perform phonemic analysis and conversion of written symbols to phonological units of speech (grapheme-to-phoneme conversion); two central cognitive processes that mediate reading acquisition. Furthermore, it has been assumed that, in contrast to cultural diversities, dyslexia in different languages has a universal biological origin. Here we show using functional magnetic resonance imaging with reading-impaired Chinese children and associated controls, that functional disruption of the left middle frontal gyrus is associated with impaired reading of the Chinese language (a logographic rather than alphabetic writing system). Reading impairment in Chinese is manifested by two deficits: one relating to the conversion of graphic form (orthography) to syllable, and the other concerning orthography-to-semantics mapping. Both of these processes are critically mediated by the left middle frontal gyrus, which functions as a centre for fluent Chinese reading that coordinates and integrates various information about written characters in verbal and spatial working memory. This finding provides an insight into the fundamental pathophysiology of dyslexia by suggesting that rather than having a universal origin, the biological abnormality of impaired reading is dependent on culture.

Children's reading performance is correlated with white matter structure measured by diffusion tensor imaging

We investigated the white matter structure in children (n = 14) with a wide range of reading performance levels using diffusion tensor imaging (DTI), a form of magnetic resonance imaging. White matter structure in a left temporo-parietal region that had been previously described as covarying with reading skill in adult readers also differs between children who are normal and poor readers. Specifically, the white matter structure measured using fractional anisotropy (FA) and coherence index (CI) significantly correlated with behavioral measurements of reading, spelling, and rapid naming performance. In general, lower anisotropy and lower coherence were associated with lower performance scores. Although the magnitude of the differences in children are smaller than those in adults, the results support the hypothesis that the structure of left temporoparietal neural pathways is a significant component of the neural system needed to develop fluent reading.

Functional and morphometric brain dissociation between dyslexia and reading ability

In functional neuroimaging studies, individuals with dyslexia frequently exhibit both hypoactivation, often in the left parietotemporal cortex, and hyperactivation, often in the left inferior frontal cortex, but there has been no evidence to suggest how to interpret the differential relations of hypoactivation and hyperactivation to dyslexia. To address this question, we measured brain activation by functional MRI during visual word rhyme judgment compared with visual cross-hair fixation rest, and we measured gray matter morphology by voxel-based morphometry in dyslexic adolescents in comparison with (i) an age-matched group, and (ii) a reading-matched group younger than the dyslexic group but equal to the dyslexic group in reading performance. Relative to the age-matched group (n = 19; mean 14.4 years), the dyslexic group (n = 19; mean 14.4 years) exhibited hypoactivation in left parietal and bilateral fusiform cortices and hyperactivation in left inferior and middle frontal gyri, caudate, and thalamus. Relative to the reading-matched group (n = 12; mean 9.8 years), the dyslexic group (n = 12; mean 14.5 years) also exhibited hypoactivation in left parietal and fusiform regions but equal activation in all four areas that had exhibited hyperactivation relative to age-matched controls as well. In regions that exhibited atypical activation in the dyslexic group, only the left parietal region exhibited reduced gray matter volume relative to both control groups. Thus, areas of hyperactivation in dyslexia reflected processes related to the level of current reading ability independent of dyslexia. In contrast, areas of hypoactivation in dyslexia reflected functional atypicalities related to dyslexia itself, independent of current reading ability, and related to atypical brain morphology in dyslexia.

The role of phonological awareness and visual-orthographic skills in Chinese reading acquisition

This study examined the role of phonological awareness and visual-orthographic skills in Chinese reading acquisition. The subjects were 154 1st, 2nd, 3rd, and 5th graders in Beijing who had learned an alphabetic script known as Hanyu Pinyin to help read Chinese characters. Childrens performance on tests of various cognitive skills, reading ability, and pinyin knowledge were examined. Results of hierarchical regression analyses showed that (a) visual skills predicted reading success at lower grades; (b) pinyin knowledge and the ability to discriminate homophonic characters predicted reading success in Grades 2, 3, and 5; and (c) onset-rime awareness, but not phonemic awareness, predicted Chinese reading. This suggests that learning to read Chinese progresses from a logographic phase to an orthographic-phonological phase and that the nature of phonological awareness predicting reading success is contingent on the characteristics of the writing system.

Neural Basis of Dyslexia: A Comparison between Dyslexic and Nondyslexic Children Equated for Reading Ability

Adults and children with developmental dyslexia exhibit reduced parietotemporal activation in functional neuroimaging studies of phonological processing. These studies used age-matched and/or intelligence quotient-matched control groups whose reading ability and scanner task performance were often superior to that of the dyslexic group. It is unknown, therefore, whether differences in activation reflect simply poorer performance in the scanner, the underlying level of reading ability, or more specific neural correlates of dyslexia. To resolve this uncertainty, we conducted a functional magnetic resonance imaging study, with a rhyme judgment task, in which we compared dyslexic children with two control groups: age-matched children and reading-matched children (younger normal readers equated for reading ability or scanner-performance to the dyslexic children). Dyslexic children exhibited reduced activation relative to both age-matched and reading-matched children in the left parietotemporal cortex and five other regions, including the right parietotemporal cortex. The dyslexic children also exhibited reduced activation bilaterally in the parietotemporal cortex when compared with children equated for task performance during scanning. Nine of the 10 dyslexic children exhibited reduced left parietotemporal activation compared with their individually selected age-matched or reading-matched control children. Additionally, normal reading fifth graders showed more activation in the same bilateral parietotemporal regions than normal-reading third graders. These findings indicate that the activation differences seen in the dyslexic children cannot be accounted for by either current reading level or scanner task performance, but instead represent a distinct developmental atypicality in the neural systems that support learning to read.

A structural-functional basis for dyslexia in the cortex of Chinese readers

Developmental dyslexia is a neurobiologically based disorder that affects ≈5–17% of school children and is characterized by a severe impairment in reading skill acquisition. For readers of alphabetic (e.g., English) languages, recent neuroimaging studies have demonstrated that dyslexia is associated with weak reading-related activity in left temporoparietal and occipitotemporal regions, and this activity difference may reflect reductions in gray matter volume in these areas. Here, we find different structural and functional abnormalities in dyslexic readers of Chinese, a nonalphabetic language. Compared with normally developing controls, children with impaired reading in logographic Chinese exhibited reduced gray matter volume in a left middle frontal gyrus region previously shown to be important for Chinese reading and writing. Using functional MRI to study language-related activation of cortical regions in dyslexics, we found reduced activation in this same left middle frontal gyrus region in Chinese dyslexics versus controls, and there was a significant correlation between gray matter volume and activation in the language task in this same area. By contrast, Chinese dyslexics did not show functional or structural (i.e., volumetric gray matter) differences from normal subjects in the more posterior brain systems that have been shown to be abnormal in alphabetic-language dyslexics. The results suggest that the structural and functional basis for dyslexia varies between alphabetic and nonalphabetic languages.

Distinct brain regions associated with syllable and phoneme

The syllable and the phoneme are two important units in the phonological structure of speech sounds. In the brain mapping literature, it remains unsolved as to whether there are separate brain regions mediating the processing of syllables and phonemes. Using functional magnetic resonance imaging (fMRI), we investigated the neural substrate of these phonological units with Chinese subjects. Results revealed that the left middle frontal cortex contributes to syllabic processing, whereas the left inferior prefrontal gyri contributes to phonemic processing. This pattern of findings offers compelling evidence for distinct cortical areas relevant to the representation of syllables and phonemes. Hum. Brain Mapping 18:201–207, 2003.

China's language input system in the digital age affects children's reading development.

Written Chinese as a logographic system was developed over 3,000 y ago. Historically, Chinese children have learned to read by learning to associate the visuo-graphic properties of Chinese characters with lexical meaning, typically through handwriting. In recent years, however, many Chinese children have learned to use electronic communication devices based on the pinyin input method, which associates phonemes and English letters with characters. When children use pinyin to key in letters, their spelling no longer depends on reproducing the visuo-graphic properties of characters that are indispensable to Chinese reading, and, thus, typing in pinyin may conflict with the traditional learning processes for written Chinese. We therefore tested character reading ability and pinyin use by primary school children in three Chinese cites: Beijing (n = 466), Guangzhou (n = 477), and Jining (n = 4,908). Children with severe reading difficulty are defined as those who were normal in nonverbal IQ but two grades (i.e., 2 y) behind in character-reading achievement. We found that the overall incidence rate of severe reading difficulty appears to be much higher than ever reported on Chinese reading. Crucially, we found that children’s reading scores were significantly negatively correlated with their use of the pinyin input method, suggesting that pinyin typing on e-devices hinders Chinese reading development. The Chinese language has survived the technological challenges of the digital era, but the benefits of communicating digitally may come with a cost in proficient learning of written Chinese.

Activity levels in the left hemisphere caudate–fusiform circuit predict how well a second language will be learned

How second language (L2) learning is achieved in the human brain remains one of the fundamental questions of neuroscience and linguistics. Previous neuroimaging studies with bilinguals have consistently shown overlapping cortical organization of the native language (L1) and L2, leading to a prediction that a common neurobiological marker may be responsible for the development of the two languages. Here, by using functional MRI, we show that later skills to read in L2 are predicted by the activity level of the fusiform–caudate circuit in the left hemisphere, which nonetheless is not predictive of the ability to read in the native language. We scanned 10-y-old children while they performed a lexical decision task on L2 (and L1) stimuli. The subjects’ written language (reading) skills were behaviorally assessed twice, the first time just before we performed the fMRI scan (time 1 reading) and the second time 1 y later (time 2 reading). A whole-brain based analysis revealed that activity levels in left caudate and left fusiform gyrus correlated with L2 literacy skills at time 1. After controlling for the effects of time 1 reading and nonverbal IQ, or the effect of in-scanner lexical performance, the development in L2 literacy skills (time 2 reading) was also predicted by activity in left caudate and fusiform regions that are thought to mediate language control functions and resolve competition arising from L1 during L2 learning. Our findings suggest that the activity level of left caudate and fusiform regions serves as an important neurobiological marker for predicting accomplishment in reading skills in a new language.

Altered functional connectivity in persistent developmental stuttering

Persistent developmental stuttering (PDS) is a speech disorder that impairs communication skills. Despite extensive research, the core causes of PDS are elusive. Converging evidence from task-induced neuroimaging methods has demonstrated the contributions of the basal ganglia and the cerebellum to PDS, but such task-state neuroimaging findings are often confounded by behavioral performance differences between subjects who stutter and normal controls. Here, using resting-state functional magnetic resonance imaging, we investigated functional connectivity within cerebellar-cortical and basal ganglia-thalamocortical networks in 16 adults who stutter and 18 age-matched fluent speakers. Seed-to-voxel analysis demonstrated that, compared to controls, adults who stutter showed alternations in functional connectivity of cerebellum to motor cortex as well as connectivity among different locals within cerebellum. Additionally, we found that functional connectivity within cerebellar circuits was significantly correlated with severity of stuttering. The alternations of functional connectivity within basal ganglia-thalamocortical networks were identified as the reduced connectivity of the putamen to the superior temporal gyrus and inferior parietal lobules in adults who stutter. The abnormalities of resting state functional connectivity are assumed to affect language planning and motor execution critical for speaking fluently. Our findings may yield neurobiological cues to the biomarkers of PDS.