Sex Differences in White Matter Diffusivity in Children with Developmental Dyslexia.

Despite the high prevalence of developmental dyslexia in the U.S. population, research remains limited and possibly biased due to the overrepresentation of males in most dyslexic samples. Studying biological sex differences in the context of developmental dyslexia can help provide a more complete understanding of the neurological markers that underly this disorder. The current study aimed to explore sex differences in white matter diffusivity in typical and dyslexic samples in third and fourth graders. Participants were asked to complete behavioral/cognitive assessments at baseline followed by MRI scanning and diffusion-weighted imaging sequences. A series of ANOVAs were conducted for comparing group membership (developmental dyslexia or typically developing), gender status (F/M), and white matter diffusivity in the tracts of interest. The Results indicated significant differences in fractional anisotropy in the left hemisphere components of the inferior and superior (parietal and temporal) longitudinal fasciculi. While males with dyslexia had lower fractional anisotropy in these tracts compared to control males, no such differences were found in females. The results of the current study may suggest that females may use a more bilateral/alternative reading network.

Preliminary evidence of prolonged timing effects of theta-burst stimulation in the reading system.

Theta-burst stimulation (TBS) is a repetitive transcranial magnetic stimulation technique that can be used to upregulate or downregulate different brain regions. However, the timing of its effects and the differing effects of continuous TBS (cTBS) versus intermittent TBS (iTBS) in the reading system have not been explored. This study assessed how stimulation type and post-stimulation timing affected change in performance during a phonological discrimination and sight word recognition task after stimulation of supramarginal gyrus (SMG). Fourteen right-handed young adults (age 18-27 years; 44% male) were block-randomized to receive either iTBS or cTBS to the supramarginal gyrus. Participants then performed a pseudoword discrimination task and an orthographic awareness task (behavioral control) at four different time points and change in reaction time compared to baseline was measured from each time point. There was no effect of stimulation type on change in reaction time [t(16) = -0.2, p = 0.9], suggesting that both types of TBS caused similar effects. Percent change in reaction time decreased over time in the pseudoword task [t(50) = -5.9, p < 0.001], indicating faster pseudoword processing speed with better performance 60-70 min after stimulation. In contrast, no change was demonstrated over time for the behavioral control task [t(43) = -0.6, p = 0.6], suggesting that the change over time seen in the test condition was not a learning effect. These findings provide insight into the effects of TBS on the reading system and can guide future study designs.

Properties of white matter tract diffusivity in children with developmental dyslexia and comorbid attention deficit/hyperactivity disorder.

BACKGROUND: Developmental dyslexia (DD) and attention deficit/hyperactivity disorder (ADHD) are highly comorbid neurodevelopmental disorders. Individuals with DD or ADHD have both been shown to have deficits in white matter tracts associated with reading and attentional control networks. However, white matter diffusivity in individuals comorbid with both DD and ADHD (DD + ADHD) has not been specifically explored. METHODS: Participants were 3rd and 4th graders (age range = 7 to 11 years; SD = 0.69) from three diagnostic groups ((DD (n = 40), DD + ADHD (n = 22), and typical developing (TD) (n = 20)). Behavioral measures of reading and attention alongside measures of white matter diffusivity were collected for all participants. RESULTS: DD + ADHD and TD groups differed in mean fractional anisotropy (FA) for the left and right Superior Longitudinal Fasciculus (SLF)-Parietal Terminations and SLF-Temporal Terminations. Mean FA for the DD group across these SLF tracts fell between the lower DD + ADHD and higher TD averages. No differences in mean diffusivity nor significant brain-behavior relations were found. CONCLUSIONS: Findings suggest that WM diffusivity in the SLF increases along a continuum across DD + ADHD, DD, and TD.

The Impact of Transcranial Magnetic Stimulation on Reading Processes: A Systematic Review.

The current systematic review examines the behavioral effects of TMS on reading. Transcranial magnetic stimulation (TMS) to targeted nodes of the brain's reading network has been shown to impact reading. Extracted data included (a) study characteristics, (b) methodology, (c) targeted nodes, (d) control paradigm, (e) type of reading task, (f) adverse effects, and (g) main findings. Data was classified by type of reading task: 1) phonological processing, 2) semantic judgment, 3) lexical decision, 4) whole word reading, and 5) visual or text characteristics. Seventy records from 46 studies (n = 844) were identified. Results indicate that TMS modulates semantic judgments when focused in the anterior aspects of the reading circuit, phonological processes after stimulation within the dorsal circuit, and impacts single word recognition and contextual reading when administered to the ventral circuit. Findings suggest that changes in specific behavioral aspects of reading following TMS may contribute to identification of foci for use as part of reading interventions.

Examining individual differences in reading and attentional control networks utilizing an oddball fMRI task.

The aim of the current study was to develop an fMRI task capable of characterizing individual differences in reading and attentional domains. Forty-nine students with a range of reading and attentional control abilities completed an event-related fMRI oddball task consisting of printed word and false font stimuli. Reading network activation was assessed by contrasting printed words with false font stimuli. Left inferior frontal gyrus and superior/middle temporal gyrus showed a main effect of stimulus type. The magnitude of the difference in activation between words and false font was correlated with word reading for both regions and reading fluency for superior/middle temporal gyrus. Regions including bilateral middle cingulate, insula and right inferior frontal gyrus showed a main effect of trial type. The difference in activation between oddball and standard trials in the right superior/middle temporal gyrus and left cerebellum was correlated with attentional control measures. Results indicate the task tapped both reading and attentional control resources. Understanding the contribution of the neural networks supporting each of these domains may provide insight into the shared neural deficits underlying the co-morbidity between developmental dyslexia and attention deficit hyperactivity disorder.

Are Shunt Revisions Associated with IQ in Congenital Hydrocephalus? A Meta -Analysis.

Although it is generally acknowledged that shunt revisions are associated with reductions in cognitive functions in individuals with congenital hydrocephalus, the literature yields mixed results and is inconclusive. The current study used meta-analytic methods to empirically synthesize studies addressing the association of shunt revisions and IQ in individuals with congenital hydrocephalus. Six studies and three in-house datasets yielded 11 independent samples for meta-analysis. Groups representing lower and higher numbers of shunt revisions were coded to generate effect sizes for differences in IQ scores. Mean effect size across studies was statistically significant, but small (Hedges' g = 0.25, p < 0.001, 95 % CI [0.08, 0.43]) with more shunt revisions associated with lower IQ scores. Results show an association of lower IQ and more shunt revisions of about 3 IQ points, a small effect, but within the error of measurement associated with IQ tests. Although clinical significance of this effect is not clear, results suggest that repeated shunt revisions because of shunt failure is associated with a reduction in cognitive functions.

The Contribution of Attentional Control and Working Memory to Reading Comprehension and Decoding.

Little is known about how specific components of working memory, namely, attentional processes including response inhibition, sustained attention, and cognitive inhibition, are related to reading decoding and comprehension. The current study evaluated the relations of reading comprehension, decoding, working memory, and attentional control in 1,134 adolescent students. Path analyses were used to assess the direct and indirect effects of working memory and aspects of attentional control on reading comprehension and decoding. There were significant direct effects of working memory, sustained attention, and cognitive inhibition on reading comprehension, but not decoding. There was a significant direct effect of working memory and response inhibition on decoding, but not comprehension. These results suggest that different aspects of attentional control are important for decoding versus comprehension.