Effects of a Phonological Intervention on EEG Connectivity Dynamics in Dyslexic Children

We examined the brain networks and oscillatory dynamics, inferred from EEG recordings during a word-reading task, of a group of children in grades 4 and 5 (ages 9–11), some of whom were dyslexic. We did this in order to characterize the differences in these dynamics between typical and dyslexic readers, and to begin to characterize the effect of a phonological intervention on those differences. Dyslexic readers were recorded both before and after they participated in a FastForWord (FFW) reading training program for approximately six months and typical readers were recorded once during this period. Before FFW dyslexic readers showed (i) a bottleneck in letter recognition areas, (ii) expansion in activity and connectivity into the right hemisphere not seen in typical readers, and (iii) greater engagement of higher-level language areas, even for consonant string stimuli. After FFW, dyslexic readers evinced a significant reduction in the engagement of language processing areas, and more activity and connectivity expanding to frontal areas, more resembling typical readers. Reduction of connectivity was negatively correlated with gains in reading performance, suggesting an increase in communication efficiency. Training appeared to improve the efficiency of the alternative (bilateral) pathways already used by the dyslexic readers, rather than inducing them to create new pathways more similar to those employed by typical readers

Brain connectivity dynamics of reading and dyslexia : typical and perturbed reading networks in adults and children

Developmental dyslexia is a language-based learning disability characterized by impaired reading speed and accuracy, poor spelling, and poor decoding abilities, despite normal intelligence. Neuroimaging investigations have identified brain regions critical for reading; few studies, however, have characterized how those regions interact to form networks and how those networks are perturbed in individuals with dyslexia. Advances in electroencephalography (EEG) analysis techniques now allow for intricate examination of these networks by focusing on individual frequency bands that comprise the brain signals. This study used EEG across several experiments to examine theta- and gamma-band connectivity patterns—first in the brains of adults, and then in dyslexic and typically-developing children during reading tasks. I investigated: 1) the ways in which the reading networks of typical and dyslexic readers differ, and 2) whether targeted reading interventions reduce these differences over time. Results show that dyslexic children generated greater occipito-temporal connectivity at critical time points in response to words and word-like stimuli, as well as increased engagement of higher-level language areas even for stimuli lacking linguistic content (e.g. consonant strings). After six months, the networks of dyslexic readers resembled those of their typically-developing counterparts for simple orthographic processing, but continued to utilize existing alternative pathways when engaging in higher-level language processes (e.g. phonology). This suggests that performance improvements in dyslexic readers are not necessarily related to changes to the typical left-lateralization of reading networks. These findings are in line with existing frameworks of dyslexia, and highlight the value of connectivity measures in understanding the neural underpinnings of word reading.Arts, Faculty ofPsychology, Department ofGraduat

Connectivity in cortical networks during word reading

The neural processes underlying word reading remain much of a mystery. In particular, the flow of information within and between language networks during word reading has not been adequately explored. The present study investigated local spectral power changes and functional and effective (causal) connectivity at each stage of word reading. EEG was used to record brain activity from healthy volunteers (n = 15), during a reading task. Independent component analysis yielded multiple sources of activation previously identified with fMRI and PET as being crucial to word reading. A combination of event-related spectral perturbation and phase synchrony analyses was performed on these independent components. Additionally, analyses of transfer entropy were conducted to investigate the possible causal information flow between sites of interest. Results confirm the VWFA as a central hub for word reading, showing a progression of theta band phase synchrony with early visual areas and then later with high-level language processing areas. Transfer entropy analyses largely converged with the theta synchrony results, again emphasizing the VWFA as a crucial node in the reading network, initially receiving information from early visual cortex, and then sending information to high-level areas. These results highlight the interplay between local and long-distance neural dynamics involved at each stage of processing during reading. Additionally, these measures of functional and causal connectivity may be used as a benchmark for comparison with clinical populations (e.g. individuals with certain kinds of dyslexia), such that disturbances in connectivity may provide insight as to underlying neurological problems.Arts, Faculty ofPsychology, Department ofGraduat

Fast Dynamics of Cortical Functional and Effective Connectivity during Word Reading

We describe for the first time the fast dynamics of functional and effective (causal) connectivity during word reading. Independent component analysis of high-density EEG recorded during a word reading task recovered multiple sources of electrical brain activity previously identified by fMRI and PET. Results confirmed the ventral occipito-temporal cortex (vOT) as a central hub for word reading, showing a progression of theta-band (3–7 Hz) and gamma-band (30–50 Hz) phase synchronization and directed theta-band and gamma-band information flow with both early visual areas and high-level language-processing areas. These results highlight the interplay between local and long-distance neural dynamics involved at each stage of the reading process. Moreover, these measures of functional and causal connectivity dynamics may be used as a benchmark for comparison with clinical populations (e.g. individuals with developmental dyslexia), such that disturbances in connectivity dynamics may provide insight as to underlying neurological problems with language processing, and their potential remediation

The temporal evolution of functional and effective connectivity after viewing a word.

<p>All connectivity analyses were computed over the span of the entire 6(<b>a</b>) Theta-band PLVs (significant functional connectivity, black lines – see Methods) among all ROIs, evolving over the course of viewing a word. (<b>b</b>) Theta-band PLVs relative to vOT. These depictions of connectivity are derived from (a), isolated to bring focus to vOT’s widespread involvement in the reading network. (<b>c</b>) Theta-band NBTE (causal connectivity, black arrows mean that NBTE was significantly different from 0 in both 50-ms bins in 100-ms interval – see Methods) relative to vOT, showing a comparable pattern of network engagement to PLVs (b). This also highlights some of the uni- and bi-directional relationships that exist in the time-course of word reading. (<b>d</b>) Gamma PLVs show similarities to their theta counterparts, albeit with sparser connectivity overall. This is further highlighted when vOT gamma interactions are isolated in (<b>e</b>), illustrating their confinement to posterior cortices. (<b>f</b>) Gamma-band NBTE (black arrows) relative to vOT, showing a comparable, and perhaps even more robust, pattern of network engagement relative to PLVs (e).</p

Scalp topographic maps of ICs.

<p>(a) Topographic maps of group average ICs for the ROIs shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088940#pone-0088940-g002" target="_blank">Figure 2</a>. (b) Topographic maps of the individual participants’ ICs for the vOT illustrate their resemblance to the group average IC. Results are similar for other ROIs. vOT ventral occipito-temporal cortex; AG angular gyrus; STG superior temporal gyrus; IFG inferior frontal gyrus; d dorsal; v ventral.</p

A schematic of the stimulus presentation and task.

<p>After a three letter sequence is presented, volunteers must respond as quickly as possible with regard to whether or not the word that appeared matched the word spelled by the letter sequence that came before it.</p

Selected dipole clusters in three-dimensional Talairach space.

<p>ICA and dipole fitting yielded multiple regions related to reading. Within each horizontal slice, individual participants’ ICs are represented by blue dots. Red dots are the cluster centroids; for each cluster the average residual variance of included ICs is less than 6.5% (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088940#pone-0088940-t001" target="_blank">Table 1</a>). The indicated z-coordinates are those of the cluster centroids (red dots). vOT ventral occipito-temporal cortex; AG angular gyrus; STG superior temporal gyrus; IFG inferior frontal gyrus; d dorsal; v ventral.</p

Average ERSPs for the IC clusters.

<p>Power in dB with respect to a baseline from −250 to −50 before presentation of the first letter. All ROIs show a prominent burst in theta (3–7 Hz) power, the earliest activity occurring immediately after word presentation (<50 ms), and the latest occurring ∼600 ms after the onset of the word. vOT ventral occipito-temporal cortex; AG angular gyrus; STG superior temporal gyrus; IFG inferior frontal gyrus; d dorsal; v ventral.</p

Expression and phylogeny of candidate genes for sex differentiation in a primitive fish species, the Siberian sturgeon, Acipenser baerii

International audienceThe molecular mechanisms underlying testis differentiation in basal actinopterygian fish remains poorly understood. The sex differentiation period was investigated in the Siberian sturgeon, Acipenser baerii, by expression profiling of Sertoli cell transcription factors (dmrt1, sox9) that control testis differentiation in vertebrates; Leydig cell factors (cyp17a1, star) affecting androgen production; the androgen receptor (ar); a growth factor controlling testis development (igf1); and a gene coding for a gonadotropin hormone (lh). Two genes were characterised for the first time in the Siberian sturgeon (dmrt1, cyp17a1), while the others came from public databases. Sturgeon gonad development is very slow, with a late sexual differentiation time during their juvenile stage, and are still immature at 3 years of age. Immature fish showed a sex-dimorphic pattern; all the genes studied displayed a higher expression level in male gonads. We took advantage of the presence of juvenile fish with pre- and post-differentiated gonads (16 and 18 months old) to characterise them at the molecular level. The post-differentiated fish displayed a sex dimorphism of gene expression in their gonads for all genes studied, with the exception of sox9. The trends in undifferentiated fish lead us to propose that sturgeons undergoing male differentiation express high levels of Sertoli cell factors (dmrt1, sox9) and of genes involved in the production and receptivity of androgens (cyp17a1, star and ar) together with lh. Expression profiles and phylogenetic studies suggest that these genes are potential regulators of testis development in the Siberian sturgeon.Mol. Reprod. Dev. 79: 504-504, 2012. (C) 2012 Wiley Periodicals, Inc