Astrid De Vos

Atypical structural asymmetry of the planum temporale is related to family history of dyslexia

Research on the neural correlates of developmental dyslexia indicates atypical anatomical lateralization of the planum temporale, a higher-order cortical auditory region. Yet whether this atypical lateralization precedes reading acquisition and is related to a familial risk for dyslexia is not currently known. In this study, we address these questions in 2 separate cohorts of young children and adolescents with and without a familial risk for dyslexia. Planum temporale surface area was manually labeled bilaterally, on the T1-weighted MR brain images of 54 pre-readers (mean age: 6.2 years, SD: 3.2 months; 33 males) and 28 adolescents (mean age: 14.7 years, SD: 3.3 months; 11 males). Half of the pre-readers and adolescents had a familial risk for dyslexia. In both pre-readers and adolescents, group comparisons of left and right planum temporale surface area showed a significant interaction between hemisphere and family history of dyslexia, with participants who had no family risk for dyslexia showing greater leftward asymmetry of the planum temporale. This effect was confirmed when analyses were restricted to normal reading participants. Altered planum temporale asymmetry thus seems to be related to family history of dyslexia.

Atypical neural synchronization to speech envelope modulations in dyslexia

HIGHLIGHTSAuditory steady‐state responses measure synchronization of neural oscillations in the auditory cortices.Specific oscillatory bands are addressed using different speech envelope modulations.Dyslexic readers show reduced alpha synchronization to syllabic rates (10 Hz).Dyslexic readers show enhanced beta synchronization to phonemic rates (20 Hz).Bottom‐up and top‐down neural processes relate auditory synchronization to reading and phonology. ABSTRACT A fundamental deficit in the synchronization of neural oscillations to temporal information in speech could underlie phonological processing problems in dyslexia. In this study, the hypothesis of a neural synchronization impairment is investigated more specifically as a function of different neural oscillatory bands and temporal information rates in speech. Auditory steady‐state responses to 4, 10, 20 and 40 Hz modulations were recorded in normal reading and dyslexic adolescents to measure neural synchronization of theta, alpha, beta and low‐gamma oscillations to syllabic and phonemic rate information. In comparison to normal readers, dyslexic readers showed reduced non‐synchronized theta activity, reduced synchronized alpha activity and enhanced synchronized beta activity. Positive correlations between alpha synchronization and phonological skills were found in normal readers, but were absent in dyslexic readers. In contrast, dyslexic readers exhibited positive correlations between beta synchronization and phonological skills. Together, these results suggest that auditory neural synchronization of alpha and beta oscillations is atypical in dyslexia, indicating deviant neural processing of both syllabic and phonemic rate information. Impaired synchronization of alpha oscillations in particular demonstrated to be the most prominent neural anomaly possibly hampering speech and phonological processing in dyslexic readers.

Source Analysis Of Auditory Steady-State Responses In Acoustic And Electric Hearing

ABSTRACT Speech is a complex signal containing a broad variety of acoustic information. For accurate speech reception, the listener must perceive modulations over a range of envelope frequencies. Perception of these modulations is particularly important for cochlear implant (CI) users, as all commercial devices use envelope coding strategies. Prolonged deafness affects the auditory pathway. However, little is known of how cochlear implantation affects the neural processing of modulated stimuli. This study investigates and contrasts the neural processing of envelope rate modulated signals in acoustic and CI listeners. Auditory steady‐state responses (ASSRs) are used to study the neural processing of amplitude modulated (AM) signals. A beamforming technique is applied to determine the increase in neural activity relative to a control condition, with particular attention paid to defining the accuracy and precision of this technique relative to other tomographies. In a cohort of 44 acoustic listeners, the location, activity and hemispheric lateralisation of ASSRs is characterised while systematically varying the modulation rate (4, 10, 20, 40 and 80 Hz) and stimulation ear (right, left and bilateral). We demonstrate a complex pattern of laterality depending on both modulation rate and stimulation ear that is consistent with, and extends, existing literature. We present a novel extension to the beamforming method which facilitates source analysis of electrically evoked auditory steady‐state responses (EASSRs). In a cohort of 5 right implanted unilateral CI users, the neural activity is determined for the 40 Hz rate and compared to the acoustic cohort. Results indicate that CI users activate typical thalamic locations for 40 Hz stimuli. However, complementary to studies of transient stimuli, the CI population has atypical hemispheric laterality, preferentially activating the contralateral hemisphere. HIGHLIGHTSBeamforming analysis of auditory steady state responses to a range of modulation rates.Accuracy and precision of beamforming method is investigated.Source analysis of electrically evoked auditory steady‐state responses.Cochlear implant population shows atypical hemispheric laterality of steady state responses.

Do prereaders’ auditory processing and speech perception predict later literacy?

Developmental dyslexia has frequently been linked to deficits in auditory processing and speech perception. However, the presence and precise nature of these deficits and the direction of their relation with reading, remains debated. In this longitudinal study, 87 five-year-olds at high and low family risk for dyslexia were followed before and during different stages of reading acquisition. The processing of different auditory cues was investigated, together with performance on speech perception and phonology and reading. Results show no effect of family risk for dyslexia on prereading auditory processing and speech perception skills. However, a relation is present between the performance on these skills in kindergarten and later phonology and literacy. In particular, links are found with the auditory processing of cues characteristic for the temporal speech amplitude envelope, rather than with other auditory cues important for speech intelligibility. Hereby, cues embedded in the speech amplitude envelope show to be related to a broad range of phonological precursors for reading. In addition, speech-in-noise perception demonstrates to operate as the most contributing factor for later phonological awareness and to be a predictor for reading mediated by the association with phonology. This study provides behavioral support for the link between prereading speech amplitude envelope processing and speech perception for future phonology and reading.

Neural organization of ventral white matter tracts parallels the initial steps of reading development: A DTI tractography study

HighlightsPre‐reading cognitive measures are sustained by broad ventral white matter network.The left ventral IFOF serves as a lexical reading route.The left IFOF is specialized for orthographic knowledge before reading instruction.Ventral white matter is not involved in phonological processing. ABSTRACT Insight in the developmental trajectory of the neuroanatomical reading correlates is important to understand related cognitive processes and disorders. In adults, a dual pathway model has been suggested encompassing a dorsal phonological and a ventral orthographic white matter system. This dichotomy seems not present in pre‐readers, and the specific role of ventral white matter in reading remains unclear. Therefore, the present longitudinal study investigated the relation between ventral white matter and cognitive processes underlying reading in children with a broad range of reading skills (n = 61). Ventral pathways of the reading network were manually traced using diffusion tractography: the inferior fronto‐occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF) and uncinate fasciculus (UF). Pathways were examined pre‐reading (5–6 years) and after two years of reading acquisition (7–8 years). Dimension reduction for the cognitive measures resulted in one component for pre‐reading cognitive measures and a separate phonological and orthographic component for the early reading measures. Regression analyses revealed a relation between the pre‐reading cognitive component and bilateral IFOF and left ILF. Interestingly, exclusively the left IFOF was related to the orthographic component, whereas none of the pathways was related to the phonological component. Hence, the left IFOF seems to serve as the lexical reading route, already in the earliest reading stages.

Grapheme-Phoneme Learning in an Unknown Orthography: A Study in Typical Reading and Dyslexic Children

In this study, we examined the learning of new grapheme-phoneme correspondences in individuals with and without dyslexia. Additionally, we investigated the relation between grapheme-phoneme learning and measures of phonological awareness, orthographic knowledge and rapid automatized naming, with a focus on the unique joint variance of grapheme-phoneme learning to word and non-word reading achievement. Training of grapheme-phoneme associations consisted of a 20-min training program in which eight novel letters (Hebrew) needed to be paired with speech sounds taken from the participants native language (Dutch). Eighty-four third grade students, of whom 20 were diagnosed with dyslexia, participated in the training and testing. Our results indicate a reduced ability of dyslexic readers in applying newly learned grapheme-phoneme correspondences while reading words which consist of these novel letters. However, we did not observe a significant independent contribution of grapheme-phoneme learning to reading outcomes. Alternatively, results from the regression analysis indicate that failure to read may be due to differences in phonological and/or orthographic knowledge but not to differences in the grapheme-phoneme-conversion process itself.