Convergent and divergent fMRI responses in children and adults to increasing language production demands

In adults, patterns of neural activation associated with perhaps the most basic language skill—overt object naming—are extensively modulated by the psycholinguistic and visual complexity of the stimuli. Do children's brains react similarly when confronted with increasing processing demands, or they solve this problem in a different way? Here we scanned 37 children aged 7–13 and 19 young adults who performed a well-normed picture-naming task with 3 levels of difficulty. While neural organization for naming was largely similar in childhood and adulthood, adults had greater activation in all naming conditions over inferior temporal gyri and superior temporal gyri/supramarginal gyri. Manipulating naming complexity affected adults and children quite differently: neural activation, especially over the dorsolateral prefrontal cortex, showed complexity-dependent increases in adults, but complexity-dependent decreases in children. These represent fundamentally different responses to the linguistic and conceptual challenges of a simple naming task that makes no demands on literacy or metalinguistics. We discuss how these neural differences might result from different cognitive strategies used by adults and children during lexical retrieval/production as well as developmental changes in brain structure and functional connectivity

Convergent and diver gent brain structural and functional abnormalities associated with developmental dyslexia

Brain abnormalities in the reading network have been repeatedly reported in individuals with developmental dyslexia (DD); however, it is still not totally understood where the structural and functional abnormalities are consistent/inconsistent across languages. In the current multimodal meta-analysis, we found convergent structural and functional alterations in the left superior temporal gyrus across languages, suggesting a neural signature of DD. We found greater reduction in grey matter volume and brain activation in the left inferior frontal gyrus in morpho-syllabic languages (e.g. Chinese) than in alphabetic languages, and greater reduction in brain activation in the left middle temporal gyrus and fusiform gyrus in alphabetic languages than in morpho-syllabic languages. These language differences are explained as consequences of being DD while learning a specific language. In addition, we also found brain regions that showed increased grey matter volume and brain activation, presumably suggesting compensations and brain regions that showed inconsistent alterations in brain structure and function. Our study provides important insights about the etiology of DD from a cross-linguistic perspective with considerations of consistency/inconsistency between structural and functional alterations

Visual word recognition insights from MEG and implications for developmental dyslexia

The ability to fluently and, seemingly effortlessly, read words is one of few uniquely special human attributes, but one which has assumed inordinate significance because of the role that this activity has come to have in modern society. A disadvantage in reading ability not only has profound personal impact for the individuals concerned, but in terms of economic and social problems also has a wider negative influence on society at large. According to current government figures in the UK, some 22% of 11 year olds do not reach the minimum standard required in English national curriculum tests. Despite its importance, however, the scientific understanding of the neural basis of reading, and more particularly the visual aspect of visual word recognition, is relatively poorly understood. Thus far, a coherent overarching model, that spans the various conceptual levels, from behaviour through functional description to neuroanatomy, has proven extraordinarily challenging to elucidate. A fuller understanding of the computational processing and neurophysiological basis of how the reading system functions would therefore represent significant progress. As with most complex behaviours, visual word recognition is thought to result from the dynamic interplay between the elements of a distributed cortical and sub-cortical network. To fully understand how visual word recognition is achieved therefore, and how it may fail in developmental dyslexia, we need to identify not only the necessary and sufficient complement of nodes that comprise this network – its functional anatomy - but we also need to understand how information flows through this network with time and indeed how the structure of the network itself may adapt in both the short and long term. In this chapter we take a historical approach to reviewing recent MEG (magnetoencephalography) research which elucidates these temporal dynamics, focusing particularly on events with the first 300ms of a visually presented word, and which we believe should set crucial constraints on models of visual word recognition and reading

Functional and structural connectivity of reading networks in the adult brain

Language processing draws upon many distributed regions in the brain. Reading in particular is a skill that emerges from the interaction between brain regions involved in phonological and orthographical processing. This project examined the reading network in adults (18-35 years old) with and without developmental dyslexia. Each participant was assessed on a comprehensive battery of standardised neuropsychological tests, which assessed IQ, reading accuracy and comprehension, spelling, phonological processing, working memory, grammatical understanding, motor coordination, and expressive and receptive language skills. In addition, each participant underwent a non-invasive MRI scan, during which structural and functional images were acquired. More specifically, T1-weighted and diffusion-weighted images were acquired to assess structural networks in the brain, whereas a simple reading task and resting-state fMRI were acquired to assess the functional networks involved in reading. Individuals with dyslexia were found to show reduced activation and reduced connectivity in regions typically associated with skilled reading. Moreover, results suggested that they rely on more effortful processing and attentional mechanisms instead to compensate for their reading difficulties. All in all, results indicated that individuals with developmental dyslexia had abnormal functional and structural brain networks related to reading performance, as well as other functions, such as working memory. These findings suggest that for successful reading remediation, it is important to focus on the integration of phonology with orthography, as well as with working memory. Literacy problems such as developmental dyslexia are thus better characterised as a complex disorder with multiple deficits rather than by a single phonological deficit

Semantic radical consistency and character transparency effects in Chinese: an ERP study

BACKGROUND: This event-related potential (ERP) study aims to investigate the representation and temporal dynamics of Chinese orthography-to-semantics mappings by simultaneously manipulating character transparency and semantic radical consistency. Character components, referred to as radicals, make up the building blocks used dur...postprin

Functional and structural neural contributions to skilled word reading

Reading is an essential skill in our everyday lives and individuals are required to process, understand, and respond to textual information at an increasingly rapid rate in order to be active participants in society. The role of spatial attention in reading has recently been emphasized, whereby better spatial attentional skills are associated with stronger reading skills, and spatial attentional training has a large impact on improving reading ability. However, the neuroanatomical correlates of reading and attention have primarily been studied in isolation. Further, there has recently been a shift to understanding how underlying white matter connectivity networks contribute to cognitive processes. However, much of the research focusing on the intersection of reading and spatial attention, as well as underlying white matter connectivity, has focused primarily on individuals with reading impairments. This thesis will focus on unraveling the neural relationship between spatial attention and reading, and how structural connectivity accounts for functional activation in reading tasks. In Chapter 2, we examine the neural relationship between lexical and sublexical reading with voluntary and reflexive spatial attention. In Experiments 1 and 2, participants performed overt reading of both lexical exception word (EW; words with inconsistent spelling-to-sound correspondences, e.g., ‘pint’) and sublexical pseudohomophone (PH; non-words that when decoded phonetically sound like real words, e.g., ‘pynt’) reading tasks, as well as tasks involving either voluntary attention (Experiment 1) or reflexive attention (Experiment 2) during functional magnetic resonance imaging (fMRI). Experiment 3 used hybrid combined reading attention tasks during fMRI, whereby the spatial attentional cue preceded presentation of the EW or PH stimulus. Overall, the results from these experiments showed that sublexical reading was more strongly associated with brain regions involved in voluntary attention, whereas lexical reading was more strongly associated with brain regions involved in reflexive attention. Thus, Experiments 1, 2 and 3 lend support to the idea that lexical and sublexical reading strategies are differentially associated with these two types of attention. In Chapter 3, we examined the extent to which fine-grained underlying white matter connectivity is able to predict fMRI activation during both lexical reading and phonetic decoding in skilled readers. Experiment 4 employed EW and PH reading and a computational modeling technique to model the relationship between whole-brain structural DTI connectivity and task-based fMRI activation during lexical and sublexical reading. Results from this study showed that brain activation during both lexical and sublexical reading in skilled readers can be accurately predicted using DTI connectivity, specifically in known reading and language areas, as well as important spatial attentional areas. Thus, this research suggests that there is a fine-grained relationship between skilled reading and extrinsic brain connectivity, showing that functional organization of reading and language can be determined (at least in part) by structural connectivity patterns. Together, the studies presented in this thesis provide valuable insight into functional and structural contributions to word reading that may serve as biomarkers of skilled reading, which in turn may have important implications for understanding and remediating reading impairments

Speech-brain synchronization: a possible cause for developmental dyslexia

152 p.Dyslexia is a neurological learning disability characterized by the difficulty in an individual¿s ability to read despite adequate intelligence and normal opportunities. The majority of dyslexic readers present phonological difficulties. The phonological difficulty most often associated with dyslexia is a deficit in phonological awareness, that is, the ability to hear and manipulate the sound structure of language. Some appealing theories of dyslexia attribute a causal role to auditory atypical oscillatory neural activity, suggesting it generates some of the phonological problems in dyslexia. These theories propose that auditory cortical oscillations of dyslexic individuals entrain less accurately to the spectral properties of auditory stimuli at distinct frequency bands (delta, theta and gamma) that are important for speech processing. Nevertheless, there are diverging hypotheses concerning the specific bands that would be disrupted in dyslexia, and which are the consequences of such difficulties on speech processing. The goal of the present PhD thesis was to portray the neural oscillatory basis underlying phonological difficulties in developmental dyslexia. We evaluated whether phonological deficits in developmental dyslexia are associated with impaired auditory entrainment to a specific frequency band. In that aim, we measured auditory neural synchronization to linguistic and non-linguistic auditory signals at different frequencies corresponding to key phonological units of speech (prosodic, syllabic and phonemic information). We found that dyslexic readers presented atypical neural entrainment to delta, theta and gamma frequency bands. Importantly, we showed that atypical entrainment to theta and gamma modulations in dyslexia could compromise perceptual computations during speech processing, while reduced delta entrainment in dyslexia could affect perceptual and attentional operations during speech processing. In addition, we characterized the links between the anatomy of the auditory cortex and its oscillatory responses, taking into account previous studies which have observed structural alterations in dyslexia. We observed that the cortical pruning in auditory regions was linked to a stronger sensitivity to gamma oscillation in skilled readers, but to stronger theta band sensitivity in dyslexic readers. Thus, we concluded that the left auditory regions might be specialized for processing phonological information at different time scales (phoneme vs. syllable) in skilled and dyslexic readers. Lastly, by assessing both children and adults on similar tasks, we provided the first evaluation of developmental modulations of typical and atypical auditory sampling (and their structural underpinnings). We found that atypical neural entrainment to delta, theta and gamma are present in dyslexia throughout the lifespan and is not modulated by reading experience

Cognitive processes and neural correlates of reading in languages with graded levels of orthographic transparency: Spanish, English and Hebrew

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis examined the cognitive processes and neural correlates involved in reading Spanish (a transparent orthography), English (an intermediate orthography) and Hebrew (an opaque orthography) by bilinguals and trilinguals. The main objectives of the five experiments were to: (i) extend previous findings which demonstrated that orthographic transparency influences the degree of reliance on lexical and sublexical processing, and (ii) assess the effects of orthographic transparency and language proficiency on strategies employed for reading in a second and third language. Word/non-word naming tasks undertaken by Spanish-English bilinguals, Hebrew-English bilinguals and English monolinguals, where frequency, length and lexicality were manipulated, showed a predominant reliance on sublexical processing in Spanish, lexical processing in Hebrew, and a balanced interplay in English. Effects of language proficiency were also observed as slower naming and lower accuracy in English as a second language. Concurrently, while showing an efficient adaptation of reading strategy to the level of orthographic transparency of English, Hebrew bilinguals appeared to show stronger reliance on sublexical processing than Spanish bilinguals, suggesting a compensatory mechanism. fMRI experiments showed that reading in all languages was associated with a common network of predominantly left-lateralised cerebral regions. Reading in each language was associated with some preferential activation within regions implicated in lexical and sublexical processing, in keeping with their graded levels of orthographic transparency. Effects of language proficiency were demonstrated as increased activation within medial frontal regions implicated in attentional processes as well as right-lateralised homologous language-processing regions. Furthermore, the patterns of activation seen in Hebrew readers in English strengthened the notion of a compensatory mechanism. Finally, a trilingual experiment replicated findings observed in bilinguals, revealed the acute complexity of reading in Hebrew as an additional language and further strengthened the concept of a compensatory mechanism in English and Spanish. The present findings further contribute to current knowledge on teaching methods, diagnostic tools and therapeutic strategies for developmental and acquired reading disorders

Phonological and semantic influences on auditory word perception in children with and without reading impairments using magnetoencephalography (MEG) and electroencephalography (EEG)

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2007.Includes bibliographical references (p. 117-135).Children with dyslexia struggle with learning to read despite adequate intelligence, motivation, and schooling. Over the years, there has been a growing consensus about the role of phonological processing in reading disability. Poor readers typically do worse than their normal reading peers on tasks that require phonological processing which has been linked, directly or indirectly, to their speech perception abilities. The work in this thesis combined behavioral, MEG, and EEG methods to examine how normal and reading-impaired children, 7-13 years of age, perceive speech under varying degrees of phonological contrast (1 vs. 3 phonetic features). In a series of auditory word perception experiments, good and poor readers were found to do worse in accuracy and/or reaction times in phonologically similar (i.e., 1-feature contrast) than phonologically dissimilar (i.e., 2 or 3-feature contrast) conditions. Despite the similar behavioral performance and EEG responses for the two groups, a region of interest (ROI) based MEG approach revealed differences in the brain activation of the two groups in superior temporal regions at 140 to 300 ms.(cont.) In the auditory word discrimination task, differences in activation were found in good readers but not poor readers, as a function of the degree of phonological contrast, reflecting poor readers' lack of sensitivity to the phonological characteristics of the word stimuli. In the sentence plausibility judgment task, the impaired phonological processing abilities of the poor readers may have led them to rely more on top-down sentence context to perceptually disambiguate phonologically confusing terminal words, thereby deceiving them into accepting the phonologically similar incongruent sentences as being congruent. This may account for the poor reader group's reduced brain activation in the phonologically demanding condition in the sentence task. The results of the experiments are consistent with a phonological view of reading disability according to which children with reading impairments have poorly defined phonological representations.by Daniel T. Wehner.Ph.D

Rapid formation and activation of lexical memory traces in human neocortex

Rapid learning of new words is crucial for language acquisition, and frequent exposure to spoken words is a key factor for the development of vocabulary. More frequently occurring (and thus more familiar) words can, in turn, be expected to have stronger memory representations than less frequent words. The neural mechanisms underlying these representations are, however, largely obscure. Even less is known about the mechanisms related to the initial acquisition of new word-forms and build-up of lexical representations. The current thesis investigated how the neural traces are activated when known and novel spoken words are perceived, and how they can be formed when novel words are first encountered and repeated. The neural processes of word memory-trace activation and rapid formation were studied in adults and children using event-related potentials. In adults, words with high frequency of occurrence elicited greater neural responses than low frequency words or meaningless pseudo-words already at ~120 ms after the time when they could be identified. Higher frequency words activated predominantly left frontal and anterior temporal cortices while the low frequency and pseudo-words showed a more bilateral temporal cortex activity. Neural dynamics during brief exposure to novel word-forms showed a rapid response increase at ~50 ms. This enhancement was associated with behaviourally-established memory performance on the novel words, confirming the relation of this neural dynamics to word learning. The enhancement, originating in the left inferior frontal and posterior temporal cortical sources, was specific to phonologically native word-forms and, furthermore, independent of whether the spoken sounds were ignored or attended to, suggesting a high degree of automaticity in native word-form acquisition. For novel word-forms with non-native phonology, such a response enhancement was not significant, while the response to known words attenuated over exposure, likely reflecting repetition-related suppression. Furthermore, individual language experience influenced the neural learning dynamics such that greater number of previously acquired non-native languages with earlier average age of acquisition predicted larger response enhancement to novel non-native word-forms whereas later average age of acquisition predicted greater increase to attended novel native words. Finally, a rapid response increase to an ignored novel native word-form in brief exposure was also observed in school-age children, and was underpinned predominantly by left prefrontal cortex and associated with writing accuracy. Remarkably, children with dyslexia failed to show such neural dynamics, suggesting deficient mechanism for automatic spoken word acquisition in dyslexia, a finding potentially relevant for further clinical research. In sum, the results suggest that exposure is key in defining the strength of perisylvian memory traces for words that can be formed rapidly and automatically in adults and typically developing children.Uusien sanojen nopea oppiminen on ratkaisevan tärkeää kielenoppimisessa ja toistuva altistuminen puhutuille sanoille on keskeistä sanavaraston kehittymisen kannalta. Toistuvammin esiintyvien (ja näin ollen tutumpien) sanojen muistiedustumien oletetaan olevan vahvempia verrattuna harvemmin esiintyvien sanojen edustumiin. Näiden edustumien taustalla olevat hermostolliset mekanismit ovat kuitenkin laajalti tuntemattomat. Vielä vähemmän tiedetään mekanismeista, jotka liittyvät uusien sanahahmojen oppimisen alkuvaiheisiin ja edustumien muodostumiseen osaksi sanastoa. Tässä väitöskirjassa selvitettiin, miten muistijäljet aivoissa aktivoituvat havaittaessa tuttuja ja uusia puhuttuja sanoja, sekä miten muistijäljet muodostuvat uusia sanoja ensi kertaa ja sen jälkeen toistuvasti kuultaessa. Muistijälkien aktivoitumisen ja nopean muodostumisen hermostollista perustaa tutkittiin aikuisilla ja lapsilla rekisteröimällä tapahtumasidonnaisia jännitevasteita. Tulokset osoittavat, että aikuisilla sanat, joilla oli korkeampi esiintymistaajuus, saivat aikaan suuremman aivovasteen kuin matalamman esiintymistaajuuden sanat tai merkityksettömät epäsanat. Vaste esiintyi jo ~120 ms sanan tunnistusajankohdan jälkeen. Korkeamman esiintymistaajuuden sanat aktivoivat pääasiallisesti vasemman otsalohkon ja etummaisen ohimolohkon aivokuoria, kun taas matalan taajuuden sanoille ja epäsanoille syntyneet vasteet havaittiin ohimolohkojen aivokuorella pään molemmin puolin. Lyhyt altistuminen uusille sanoille sai aikaan nopean aivovasteen kasvun. Tämä kasvu oli yhteydessä uusien sanojen mieleenpalauttamiseen ja tunnistamiseen altistuksen jälkeen, mikä vahvisti käsitystä, että aivovasteessa tapahtunut muutos liittyi sanojen oppimiseen. Vasteen kasvu oli peräisin vasemman aivopuoliskon alemman otsalohkon ja taemman ohimolohkon aivokuorilta. Se oli merkitsevä vain äidinkielisiä äänteitä sisältäville uusille sanoille ja esiintyi huolimatta siitä, kohdistettiinko tarkkaavaisuus sanoihin vai ei, viitaten äidinkielisten sanojen oppimisen olevan pitkälti automaattista. Vieraita äänteitä sisältäville sanoille syntyneessä vasteessa ei tapahtunut merkitsevää kasvua ja ennestään tutuille sanoille syntynyt vaste heikentyi altistumisen seurauksena todennäköisesti toistamiseen liittyvän suppression johdosta. Lisäksi kokemus kielten oppimisesta vaikutti neuraalisen oppimisen yksilölliseen vaihteluun siten, että aiemmin opeteltujen vieraiden kielten suurempi määrä yhdistettynä keskimäärin aikaisempaan aloitusikään oli yhteydessä suurempaan aivovasteen kasvuun uusille vierasperäisille sanoille. Myöhäisempi aloitusikä sen sijaan ennusti suurempaa kasvua uusille äidinkielisille sanoille. Myös kouluikäisillä lapsilla lyhyt altistuminen uusille äidinkielisille sanoille johti aivovasteen kasvamiseen. Vasteen kasvun perusta oli pääosin vasemman etuotsalohkon aivokuorella ja se oli yhteydessä kirjoitustarkkuuteen. Sen sijaan lapsilla, joilla oli lukihäiriö, ei tapahtunut vastaavanlaista vasteen kasvua viitaten puutteelliseen sanojen oppimisen aivomekanismiin lukihäiriössä. Tulosten perusteella olennaista sanojen neuraalisten muistijälkien vahvuudelle on niille altistuminen, minkä avulla muistijäljet voivat muodostua nopeasti ja automaattisesti aikuisilla ja tyypillisesti kehittyvillä lapsilla