Brain plasticity in aphasic patients: Intra- and inter-hemispheric reorganisation of the whole linguistic network probed by N150 and N350 components

The present study examined linguistic plastic reorganization of language through Evoked Potentials in a group of 17 non-fluent aphasic patients who had suffered left perisylvian focal lesions, and showed a good linguistic recovery. Language reorganisation was probed with three linguistic tasks (Phonological, Semantic, Orthographic), the early word recognition potential (N150) and the later phonological-related component (N350). Results showed the typical left-lateralised posterior N150 in healthy controls (source: left Fusiform Gyrus), that was bilateral (Semantic) or right sided (Phonological task) in patients (sources: right Inferior/Middle Temporal and Fusiform Gyri). As regards N350, controls revealed different intra- and inter-hemispheric linguistic activation across linguistic tasks, whereas patients exhibited greater activity in left intact sites, anterior and posterior to the damaged area, in all tasks (sources: Superior Frontal Gyri). A comprehensive neurofunctional model is presented, describing how complete intra- and inter-hemispheric reorganisation of the linguistic networks occurs after aphasic damage in the strategically dominant left perisylvian linguistic centres

Cultural Constraints on Brain Development: Evidence from a Developmental Study of Visual Word Processing in Mandarin Chinese

Developmental differences in phonological and orthographic processing in Chinese were examined in 9 year olds, 11 year olds, and adults using functional magnetic resonance imaging. Rhyming and spelling judgments were made to 2-character words presented sequentially in the visual modality. The spelling task showed greater activation than the rhyming task in right superior parietal lobule and right inferior temporal gyrus, and there were developmental increases across tasks bilaterally in these regions in addition to bilateral occipital cortex, suggesting increased involvement over age on visuo-orthographic analysis. The rhyming task showed greater activation than the spelling task in left superior temporal gyrus and there were developmental decreases across tasks in this region, suggesting reduced involvement over age on phonological representations. The rhyming and spelling tasks included words with conflicting orthographic and phonological information (i.e., rhyming words spelled differently or nonrhyming words spelled similarly) or nonconflicting information. There was a developmental increase in the difference between conflicting and nonconflicting words in left inferior parietal lobule, suggesting greater engagement of systems for mapping between orthographic and phonological representations. Finally, there were developmental increases across tasks in an anterior (Broadman area [BA] 45, 46) and posterior (BA 9) left inferior frontal gyrus, suggesting greater reliance on controlled retrieval and selection of posterior lexical representations

Investigating the function of the ventral visual reading pathway and its involvement in acquired reading disorders

This thesis investigated the role of the left ventral occipitotemporal (vOT) cortex and how damage to this area causes peripheral reading disorders. Functional magnetic resonance imaging (fMRI) studies in volunteers demonstrated that the left vOT is activated by written words over numbers or perceptually-matched baselines, irrespective of the word’s location on the visual field. Mixed results were observed for the comparison of words versus false font stimuli. This response profile suggests that the left vOT is preferentially activated by words or word-like stimuli, due to either: (1) bottom-up specialisation for processing familiar word-forms; (2) top-down task-dependent modulation, or (3) a combination of the two. Further studies are proposed to discriminate between these possibilities. Thirteen patients with left occipitotemporal damage participated in the rehabilitation and fMRI studies. The patients were impaired on word, text and letter reading. A structural analysis showed that damage to the left occipitotemporal white matter, in the vicinity of the inferior longitudinal fasciculus, was associated with slow word reading speed. The fMRI study showed that the patients had reduced activation of the bilateral posterior superior temporal sulci relative to controls. Activity in this area correlated with reading speed. The efficacy of intensive whole-word recognition training was tested. Immediately after the training, trained words were read faster than untrained words, but the effects did not persist until the follow-up assessment. Hence, damage to the left vOT white matter impairs rapid whole-word recognition and is resistant to rehabilitation. The final study investigated the role of spatial frequency (SF) in the lateralisation of vOT function. Lateralisation of high and low SF processing was demonstrated, concordant with the lateralisation for words and faces to the left and right vOT respectively. A perceptual basis for the organisation of vOT cortex might explain why left vOT damage is resistant to treatment

Orthographic priming in Braille reading as evidence for task-specific reorganization in the ventral visual cortex of the congenitally blind

The task-specific principle asserts that, following deafness or blindness, the deprived cortex is reorganized in a manner such that the task of a given area is preserved even though its input modality has been switched. Accordingly, tactile reading engages the ventral occipitotemporal cortex (vOT) in the blind in a similar way to regular reading in the sighted. Others, however, show that the vOT of the blind processes spoken sentence structure, which suggests that the task-specific principle might not apply to vOT. The strongest evidence for the vOT's engagement in sighted reading comes from orthographic repetition-suppression studies. Here, congenitally blind adults were tested in an fMRI repetition-suppression paradigm. Results reveal a double dissociation, with tactile orthographic priming in the vOT and auditory priming in general language areas. Reconciling our finding with other evidence, we propose that the vOT in the blind serves multiple functions, one of which, orthographic processing, overlaps with its function in the sighted

The role of visuo-spatial and verbal working memory in L2 Japanese reading proficiency

Verbal working memory is recognized as a strong predictor of L2 reading development in the area of learning new vocabulary, reading comprehension, and overall L2 proficiency in alphabetic languages such as English. However, few studies have addressed if the same is true in logographic languages such as Japanese. Previous literature has indicated that phonology plays a weaker role in reading Japanese than alphabetic languages and that visual information is often processed for semantic rather than phonetic information. Based on these findings, it was hypothesized that visuo-spatial working memory would display a stronger relationship with Japanese reading proficiency than verbal working memory. This study investigated the relationship between (a) visuo-spatial working memory and Japanese reading proficiency and (b) verbal working memory and Japanese reading proficiency. Thirty learners of Japanese as a foreign language had their visuo-spatial working memory assessed using a spatial span task and a dual 3-back task. Their verbal working memory was assessed using an automated reading span task. Participants also took a Japanese cloze test and proficiency self-rating questionnaire to indicate their reading proficiency. Correlations were not found between the visuo-spatial working memory tasks and the Japanese cloze test, but a weak correlation was found between the verbal working memory task and the Japanese cloze test. Since the reading assessment used in this study had questionable validity, the hypothesis and research questions for this study could not be fully addressed. Suggestions are made for refining assessment tools and using other techniques to help us better understand of the relationship between working memory measures and Japanese reading proficiency

Literacy development: evidence review

Literacy includes the word-level skills of word reading and spelling and the text-level skills of reading comprehension and writing composition. These skills are involved in virtually all everyday activities. As a result, poor literacy impacts on every aspect of life. Word reading, spelling, reading comprehension, and writing composition are supported by similar language and cognitive skills as well as affective and environment factors. Learning to be literate builds upon existing knowledge of the language from speech. Becoming literate then enables children to learn more about language. However, literacy is unlikely to be achieved without explicit and prolonged instruction. This review provides an evidence base for decision-making during literacy education. We identify key skills that must be in place to enable children to reach their optimum potential and highlight where weakness can suggest a need for extra support. We begin by discussing models of literacy development as these models provide a framework within which to present the evidence base for the rest of the review. We then consider the underlying skills in greater depth, beginning first with the proximal factors that underpin word-level and text-level reading and writing. Then we consider distal child-based and wider environmental factors that indirectly impact on literacy development

Sensory theories of developmental dyslexia: three challenges for research.

Recent years have seen the publication of a range of new theories suggesting that the basis of dyslexia might be sensory dysfunction. In this Opinion article, the evidence for and against several prominent sensory theories of dyslexia is closely scrutinized. Contrary to the causal claims being made, my analysis suggests that many proposed sensory deficits might result from the effects of reduced reading experience on the dyslexic brain. I therefore suggest that longitudinal studies of sensory processing, beginning in infancy, are required to successfully identify the neural basis of developmental dyslexia. Such studies could have a powerful impact on remediation.This is the accepted manuscript. The final version is available from NPG at http://www.nature.com/nrn/journal/v16/n1/abs/nrn3836.html

SELECTION IN WRITTEN LANGUAGE PRODUCTION: EVIDENCE FROM APHASIA

Most models of word production assume that in the process of producing a target word, multiple distractors also get activated, both other words (at the lexical level) and other phonemes/letters (at the segmental level). Thus, a selection mechanism is needed to select the targets at each level. While selection is one of the mechanisms that has received a considerable amount of attention in the spoken production literature, minimal amount of research has been dedicated to understanding this mechanism in written production. In fact, although written language is an integral part of our everyday life, written language production is the most under-researched language domain. The work presented in this dissertation enhances our understanding of the selection mechanisms involved in written word production. Specifically, we investigated whether the selection mechanism(s) are: (1) shared across cognitive domains (language vs non-language), (2) shared across levels of processing (lexical vs segmental), and (3) internal or external to the network that supports the mapping of representations across levels of processing. To this end, we collected behavioral data from a group of individuals with post-stroke aphasia and a group of aged-matched healthy control individuals, using two experimental tasks: the written Blocked Cyclic Naming task and the Simon visual-spatial compatibility task. Structural (gray matter) neuroimaging data were also collected for the post-stroke aphasia group. The results of the data analyses undertaken provide no evidence of a shared mechanism between the language and non-language domains investigated. With respect to levels of processing, the findings reveal that selection at the lexical and segmental levels is supported by distinct mechanisms. Finally, the evidence indicates that selection processes involved in written word production are supported by a mechanism that is external to the representational mapping system, and that this external mechanism relies on left-hemisphere inferior frontal and orbitofrontal regions of the brain. These findings significantly advance our understanding of the selection mechanisms involved in written language production, which has important theoretical implications for understanding the writing system and for theories of word production more generally, as well as having translational implications related to naming therapies in aphasia and beyond