Global Approaches to Early Learning Research and Practice: Integrative Commentary

This commentary presents highlights from the seven articles in this volume, along with a synthesis of take-home points that can be used to inform policy and practice. Across each article there is a story of both successes and the challenges of ongoing work that seeks to enhance children's development in diverse and challenging environments across the globe. Although the topics covered in this volume range from development of early self-regulation and executive function to the use of technology to aid literacy acquisition in remote areas, each points to the need for systems-level coordination and sustained commitment to reach children at risk.

Functional connectivity and activity of white matter in somatosensory pathways under tactile stimulations

Functional MRI has proven to be effective in detecting neural activity in brain cortices on the basis of blood oxygenation level dependent (BOLD) contrast, but has relatively poor sensitivity for detecting neural activity in white matter. To demonstrate that BOLD signals in white matter are detectable and contain information on neural activity, we stimulated the somatosensory system and examined distributions of BOLD signals in related white matter pathways. The temporal correlation profiles and frequency contents of BOLD signals were compared between stimulation and resting conditions, and between relevant white matter fibers and background regions, as well as between left and right side stimulations. Quantitative analyses show that, overall, MR signals from white matter fiber bundles in the somatosensory system exhibited significantly greater temporal correlations with the primary sensory cortex and greater signal power during tactile stimulations than in a resting state, and were stronger than corresponding measurements for background white matter both during stimulations and in a resting state. The temporal correlation and signal power under stimulation were found to be twice those observed from the same bundle in a resting state, and bore clear relations with the side of stimuli. These indicate that BOLD signals in white matter fibers encode neural activity related to their functional roles connecting cortical volumes, which are detectable with appropriate methods.

Mapping Lifetime Brain Volumetry with Covariate-Adjusted Restricted Cubic Spline Regression from Cross-sectional Multi-site MRI

Understanding brain volumetry is essential to understand neurodevelopment and disease. Historically, age-related changes have been studied in detail for specific age ranges (e.g., early childhood, teen, young adults, elderly, etc.) or more sparsely sampled for wider considerations of lifetime aging. Recent advancements in data sharing and robust processing have made available considerable quantities of brain images from normal, healthy volunteers. However, existing analysis approaches have had difficulty addressing (1) complex volumetric developments on the large cohort across the life time (e.g., beyond cubic age trends), (2) accounting for confound effects, and (3) maintaining an analysis framework consistent with the general linear model (GLM) approach pervasive in neuroscience. To address these challenges, we propose to use covariate-adjusted restricted cubic spline (C-RCS) regression within a multi-site cross-sectional framework. This model allows for flexible consideration of non-linear age-associated patterns while accounting for traditional covariates and interaction effects. As a demonstration of this approach on lifetime brain aging, we derive normative volumetric trajectories and 95% confidence intervals from 5111 healthy patients from 64 sites while accounting for confounding sex, intracranial volume and field strength effects. The volumetric results are shown to be consistent with traditional studies that have explored more limited age ranges using single-site analyses. This work represents the first integration of C-RCS with neuroimaging and the derivation of structural covariance networks (SCNs) from a large study of multi-site, cross-sectional data.

Comprehending text versus reading words in young readers with varying reading ability: distinct patterns of functional connectivity from common processing hubs

Skilled reading depends on recognizing words efficiently in isolation (word-level processing; WL) and extracting meaning from text (discourse-level processing; DL); deficiencies in either result in poor reading. FMRI has revealed consistent overlapping networks in word and passage reading, as well as unique regions for DL processing; however, less is known about how WL and DL processes interact. Here we examined functional connectivity from seed regions derived from where BOLD signal overlapped during word and passage reading in 38 adolescents ranging in reading ability, hypothesizing that even though certain regions support word- and higher-level language, connectivity patterns from overlapping regions would be task modulated. Results indeed revealed that the left-lateralized semantic and working memory (WM) seed regions showed task-dependent functional connectivity patterns: during DL processes, semantic and WM nodes all correlated with the left angular gyrus, a region implicated in semantic memory/coherence building. In contrast, during WL, these nodes coordinated with a traditional WL area (left occipitotemporal region). In addition, these WL and DL findings were modulated by decoding and comprehension abilities, respectively, with poorer abilities correlating with decreased connectivity. Findings indicate that key regions may uniquely contribute to multiple levels of reading; we speculate that these connectivity patterns may be especially salient for reading outcomes and intervention response.

The relation between 1st grade grey matter volume and 2nd grade math competence

Mathematical and numerical competence is a critical foundation for individual success in modern society yet the neurobiological sources of individual differences in math competence are poorly understood. Neuroimaging research over the last decade suggests that neural mechanisms in the parietal lobe, particularly the intraparietal sulcus (IPS) are structurally aberrant in individuals with mathematical learning disabilities. However, whether those same brain regions underlie individual differences in math performance across the full range of math abilities is unknown. Furthermore, previous studies have been exclusively cross-sectional, making it unclear whether variations in the structure of the IPS are caused by or consequences of the development of math skills. The present study investigates the relation between grey matter volume across the whole brain and math competence longitudinally in a representative sample of 50 elementary school children. Results show that grey matter volume in the left IPS at the end of 1st grade relates to math competence a year later at the end of 2nd grade. Grey matter volume in this region did not change over that year, and was still correlated with math competence at the end of 2nd grade. These findings support the hypothesis that the IPS and its associated functions represent a critical foundation for the acquisition of mathematical competence.

Visualizing functional pathways in the human brain using correlation tensors and magnetic resonance imaging

Functional magnetic resonance imaging usually detects changes in blood oxygenation level dependent (BOLD) signals from T2*-sensitive acquisitions, and is most effective in detecting activity in brain cortex which is irrigated by rich vasculature to meet high metabolic demands. We recently demonstrated that MRI signals from T2*-sensitive acquisitions in a resting state exhibit structure-specific temporal correlations along white matter tracts. In this report we validate our preliminary findings and introduce spatio-temporal functional correlation tensors to characterize the directional preferences of temporal correlations in MRI signals acquired at rest. The results bear a remarkable similarity to data obtained by diffusion tensor imaging but without any diffusion-encoding gradients. Just as in gray matter, temporal correlations in resting state signals may reflect intrinsic synchronizations of neural activity in white matter. Here we demonstrate that functional correlation tensors are able to visualize long range white matter tracts as well as short range sub-cortical fibers imaged at rest, and that evoked functional activities alter these structures and enhance the visualization of relevant neural circuitry. Furthermore, we explore the biophysical mechanisms underlying these phenomena by comparing pulse sequences, which suggest that white matter signal variations are consistent with hemodynamic (BOLD) changes associated with neural activity. These results suggest new ways to evaluate MRI signal changes within white matter.

Thalamo-cortical connectivity: what can diffusion tractography tell us about reading difficulties in children?

Reading is an essential skill in modern society, but many people have deficits in the decoding and word recognition aspects of reading, a difficulty often referred to as dyslexia. The primary focus of neuroimaging studies to date in dyslexia has been on cortical regions; however, subcortical regions may also be important for explaining this disability. Here, we used diffusion tensor imaging to examine the association between thalamo-cortical connectivity and children's reading ability in 20 children with typically developed reading ability (age range 8-17/10-17 years old from two imaging centers) and 19 children with developmental dyslexia (DYS) (age range 9-17/9-16 years old). To measure thalamo-cortical connections, the structural images were segmented into cortical and subcortical anatomical regions that were used as target and seed regions in the probabilistic tractography analysis. Abnormal thalamic connectivity was found in the dyslexic group in the sensorimotor and lateral prefrontal cortices. These results suggest that the thalamus may play a key role in reading behavior by mediating the functions of task-specific cortical regions; such findings lay the foundation for future studies to investigate further neurobiological anomalies in the development of thalamo-cortical connectivity in DYS.

Structural connectivity patterns associated with the putative visual word form area and children's reading ability

With the advent of neuroimaging techniques, especially functional MRI (fMRI), studies have mapped brain regions that are associated with good and poor reading, most centrally a region within the left occipito-temporal/fusiform region (L-OT/F) often referred to as the visual word form area (VWFA). Despite an abundance of fMRI studies of the putative VWFA, research about its structural connectivity has just started. Provided that the putative VWFA may be connected to distributed regions in the brain, it remains unclear how this network is engaged in constituting a well-tuned reading circuitry in the brain. Here we used diffusion MRI to study the structural connectivity patterns of the putative VWFA and surrounding areas within the L-OT/F in children with typically developing (TD) reading ability and with word recognition deficits (WRD; sometimes referred to as dyslexia). We found that L-OT/F connectivity varied along a posterior-anterior gradient, with specific structural connectivity patterns related to reading ability in the ROIs centered upon the putative VWFA. Findings suggest that the architecture of the putative VWFA connectivity is fundamentally different between TD and WRD, with TD showing greater connectivity to linguistic regions than WRD, and WRD showing greater connectivity to visual and parahippocampal regions than TD. Findings thus reveal clear structural abnormalities underlying the functional abnormalities in the putative VWFA in WRD.

Novel Approaches to Examine Passage, Student, and Question Effects on Reading Comprehension

Reading comprehension is influenced by sources of variance associated with the reader and the task. To gain insight into the complex interplay of multiple sources of influence, we employed crossed random-effects item response models. These models allowed us to simultaneously examine the degree to which variables related to the type of passage and student characteristics influenced students' (n = 94; mean age = 11.97 years) performance on two indicators of reading comprehension: different types of comprehension questions and passage fluency. We found that variables related to word recognition, language, and executive function were influential across various types of passages and comprehension questions and also predicted a reader's passage fluency. Further, an exploratory analysis of two-way interaction effects was conducted. Results suggest that understanding the relative influence of passage, question, and student variables has implications for identifying struggling readers and designing interventions to address their individual needs.

Neuroimaging of reading intervention: a systematic review and activation likelihood estimate meta-analysis

A growing number of studies examine instructional training and brain activity. The purpose of this paper is to review the literature regarding neuroimaging of reading intervention, with a particular focus on reading difficulties (RD). To locate relevant studies, searches of peer-reviewed literature were conducted using electronic databases to search for studies from the imaging modalities of fMRI and MEG (including MSI) that explored reading intervention. Of the 96 identified studies, 22 met the inclusion criteria for descriptive analysis. A subset of these (8 fMRI experiments with post-intervention data) was subjected to activation likelihood estimate (ALE) meta-analysis to investigate differences in functional activation following reading intervention. Findings from the literature review suggest differences in functional activation of numerous brain regions associated with reading intervention, including bilateral inferior frontal, superior temporal, middle temporal, middle frontal, superior frontal, and postcentral gyri, as well as bilateral occipital cortex, inferior parietal lobules, thalami, and insulae. Findings from the meta-analysis indicate change in functional activation following reading intervention in the left thalamus, right insula/inferior frontal, left inferior frontal, right posterior cingulate, and left middle occipital gyri. Though these findings should be interpreted with caution due to the small number of studies and the disparate methodologies used, this paper is an effort to synthesize across studies and to guide future exploration of neuroimaging and reading intervention.

Comprehending expository texts: the dynamic neurobiological correlates of building a coherent text representation

Little is known about the neural correlates of expository text comprehension. In this study, we sought to identify neural networks underlying expository text comprehension, how those networks change over the course of comprehension, and whether information central to the overall meaning of the text is functionally distinct from peripheral information. Seventeen adult subjects read expository passages while being scanned using functional magnetic resonance imaging (fMRI). By convolving phrase onsets with the hemodynamic response function (HRF), we were able to identify regions that increase and decrease in activation over the course of passage comprehension. We found that expository text comprehension relies on the co-activation of the semantic control network and regions in the posterior midline previously associated with mental model updating and integration [posterior cingulate cortex (PCC) and precuneus (PCU)]. When compared to single word comprehension, left PCC and left Angular Gyrus (AG) were activated only for discourse-level comprehension. Over the course of comprehension, reliance on the same regions in the semantic control network increased, while a parietal region associated with attention [intraparietal sulcus (IPS)] decreased. These results parallel previous findings in narrative comprehension that the initial stages of mental model building require greater visuospatial attention processes, while maintenance of the model increasingly relies on semantic integration regions. Additionally, we used an event-related analysis to examine phrases central to the text's overall meaning vs. peripheral phrases. It was found that central ideas are functionally distinct from peripheral ideas, showing greater activation in the PCC and PCU, while over the course of passage comprehension, central and peripheral ideas increasingly recruit different parts of the semantic control network. The finding that central information elicits greater response in mental model updating regions than peripheral ideas supports previous behavioral models on the cognitive importance of distinguishing textual centrality.

Examining the Relationship Between Word Reading Efficiency and Oral Reading Rate in Predicting Comprehension Among Different Types of Readers

To further explore contextual reading rate, an important aspect of reading fluency, we examined the relationship between word reading efficiency (WRE) and contextual oral reading rate (ORR), the degree to which they overlap across different comprehension measures, whether oral language (semantics and syntax) predicts ORR beyond contributions of word-level skills, and whether the WRE-ORR relationship varies based on different reader profiles. Assessing reading and language of average readers, poor decoders, and poor comprehenders, ages 10 to 14, ORR was the strongest predictor of comprehension across various formats; WRE contributed no unique variance after taking ORR into account. Findings indicated that semantics, not syntax, contributed to ORR. Poor comprehenders performed below average on measures of ORR, despite average WRE, expanding previous findings suggesting specific weaknesses in ORR for this group. Together, findings suggest that ORR draws upon skills beyond those captured by WRE and suggests a role for oral language (semantics) in ORR.

Simultaneous analysis and quality assurance for diffusion tensor imaging

Diffusion tensor imaging (DTI) enables non-invasive, cyto-architectural mapping of in vivo tissue microarchitecture through voxel-wise mathematical modeling of multiple magnetic resonance imaging (MRI) acquisitions, each differently sensitized to water diffusion. DTI computations are fundamentally estimation processes and are sensitive to noise and artifacts. Despite widespread adoption in the neuroimaging community, maintaining consistent DTI data quality remains challenging given the propensity for patient motion, artifacts associated with fast imaging techniques, and the possibility of hardware changes/failures. Furthermore, the quantity of data acquired per voxel, the non-linear estimation process, and numerous potential use cases complicate traditional visual data inspection approaches. Currently, quality inspection of DTI data has relied on visual inspection and individual processing in DTI analysis software programs (e.g. DTIPrep, DTI-studio). However, recent advances in applied statistical methods have yielded several different metrics to assess noise level, artifact propensity, quality of tensor fit, variance of estimated measures, and bias in estimated measures. To date, these metrics have been largely studied in isolation. Herein, we select complementary metrics for integration into an automatic DTI analysis and quality assurance pipeline. The pipeline completes in 24 hours, stores statistical outputs, and produces a graphical summary quality analysis (QA) report. We assess the utility of this streamlined approach for empirical quality assessment on 608 DTI datasets from pediatric neuroimaging studies. The efficiency and accuracy of quality analysis using the proposed pipeline is compared with quality analysis based on visual inspection. The unified pipeline is found to save a statistically significant amount of time (over 70%) while improving the consistency of QA between a DTI expert and a pool of research associates. Projection of QA metrics to a low dimensional manifold reveal qualitative, but clear, QA-study associations and suggest that automated outlier/anomaly detection would be feasible.

Not all reading disabilities are dyslexia: distinct neurobiology of specific comprehension deficits

Although an extensive literature exists on the neurobiological correlates of dyslexia (DYS), to date, no studies have examined the neurobiological profile of those who exhibit poor reading comprehension despite intact word-level abilities (specific reading comprehension deficits [S-RCD]). Here we investigated the word-level abilities of S-RCD as compared to typically developing readers (TD) and those with DYS by examining the blood oxygenation-level dependent response to words varying on frequency. Understanding whether S-RCD process words in the same manner as TD, or show alternate pathways to achieve normal word-reading abilities, may provide insights into the origin of this disorder. Results showed that as compared to TD, DYS showed abnormal covariance during word processing with right-hemisphere homologs of the left-hemisphere reading network in conjunction with left occipitotemporal underactivation. In contrast, S-RCD showed an intact neurobiological response to word stimuli in occipitotemporal regions (associated with fast and efficient word processing); however, inferior frontal gyrus (IFG) abnormalities were observed. Specifically, TD showed a higher-percent signal change within right IFG for low-versus-high frequency words as compared to both S-RCD and DYS. Using psychophysiological interaction analyses, a coupling-by-reading group interaction was found in right IFG for DYS, as indicated by a widespread greater covariance between right IFG and right occipitotemporal cortex/visual word-form areas, as well as bilateral medial frontal gyrus, as compared to TD. For S-RCD, the context-dependent functional interaction anomaly was most prominently seen in left IFG, which covaried to a greater extent with hippocampal, parahippocampal, and prefrontal areas than for TD for low- as compared to high-frequency words. Given the greater lexical access demands of low frequency as compared to high-frequency words, these results may suggest specific weaknesses in accessing lexical-semantic representations during word recognition. These novel findings provide foundational insights into the nature of S-RCD, and set the stage for future investigations of this common, but understudied, reading disorder.

Neural circuitry associated with two different approaches to novel word learning

Skilled reading depends upon successfully integrating orthographic, phonological, and semantic information; however, the process of becoming a skilled reader with efficient neural circuitry is not fully understood. Short-term learning paradigms can provide insight into learning mechanisms by revealing differential responses to training approaches. To date, neuroimaging studies have primarily focused on effects of teaching novel words either in isolation or in context, without directly comparing the two. The current study compared the behavioral and neurobiological effects of learning novel pseudowords (i.e., pronouncing and attaching meaning) trained either in isolation or in sentential context. Behavioral results showed generally comparable pseudoword learning for both conditions, but sentential context-trained pseudowords were spoken and comprehended slightly more quickly. Neurobiologically, fMRI activity for reading trained pseudowords was similar to real words; however, an interaction between training approach and reading proficiency was observed. Specifically, highly skilled readers showed similar levels of activity regardless of training approach. However, less skilled readers differentiated between training conditions, showing comparable activity to highly skilled readers only for isolation-trained pseudowords. Overall, behavioral and neurobiological findings suggest that training approach may affect rate of learning and neural circuitry, and that less skilled readers may need explicit training to develop optimal neural pathways.

Reader-Text Interactions: How Differential Text and Question Types Influence Cognitive Skills Needed for Reading Comprehension

Current research has shown that comprehension can vary based on text and question types, and that readers' word recognition and background knowledge may account for these differences. Other reader characteristics such as semantic and syntactic awareness, inferencing, planning/organizing have also all been linked to reading comprehension, but have not been examined with regard to specific text and question types. The aim of this study was to explore the relationships between reader characteristics, text types, and question types, in children aged 10-14. We sought to compare children's performance when comprehending narrative, expository, and functional text, as well as to explore differences between children's performance on comprehension questions that assess their literal or inferential comprehension of a passage. To examine such differences, we analyzed the degree to which distinct cognitive skills (semantic and syntactic awareness, inferencing, planning/organizing) contribute to performance on varying types of texts and questions. This study found main effects of text and question types, as well as an interaction in which relations between question types varied between text types. Analyses indicated that higher order cognitive skills, including the ability to make inferences and to plan and organize information, contribute to comprehension of more complex text (e.g., expository vs. narrative) and question types (e.g., inferential vs. literal), and therefore are important components of reading for later elementary and middle school students. These findings suggest that developing these skills in early elementary school may better equip students for comprehending the texts they will encounter in higher grades.

Increased regional fractional anisotropy in highly screened attention-deficit hyperactivity disorder (ADHD)

Diffusion tensor imaging data were collected at 3.0 Tesla from 16 children with attention-deficit hyperactivity disorder (ADHD) and 16 typically developing controls, ages 9 to 14 years. Fractional anisotropy images were calculated and normalized by linear transformation. Voxel-wise and atlas-based region-of-interest analyses were performed. Using voxel-wise analysis, fractional anisotropy was found to be significantly increased in the attention-deficit hyperactivity disorder group in the right superior frontal gyrus and posterior thalamic radiation, and left dorsal posterior cingulate gyrus, lingual gyrus, and parahippocampal gyrus. No regions showed significantly decreased fractional anisotropy in attention-deficit hyperactivity disorder. Region-of-interest analysis revealed increased fractional anisotropy in the left sagittal stratum, that is, white matter that connects the temporal lobe to distant cortical regions. Only fractional anisotropy in the left sagittal stratum was significantly associated with attention-deficit hyperactivity disorder symptom severity. Several recent studies have reported pathological increases in fractional anisotropy in other conditions, highlighting the relevance of diffusion tensor imaging in identifying atypical white matter structure associated with neurodevelopmental processes.

Cognitive profile of children with neurofibromatosis and reading disabilities

A large percentage of children with Neurofibromatosis Type 1(NF-1) have learning disabilities, often in the realm of reading. Previous studies have indicated that children with NF-1 show a neuropsychological profile similar to idiopathic reading disabilities (IRD); however, studies typically have not subdivided children with NF-1 into those who do and do not have RD (NF+RD and NFnoRD, respectively). The current study examined the cognitive profile of children with NF-1 with and without RD and compared them to children with IRD as well as to typically developing readers (Controls). Findings showed that children with NF+RD performed similarly to children with IRD on phonological, rapid naming, and reading comprehension measures; however, children with NF+RD displayed pronounced visual-spatial deficits as compared to IRD and Control groups. In addition, when comparing the NF-1 groups to each other as well as to the control and IRD groups, the current study reported that there were no oral language differences; lack of findings in the realm of oral language was attributed to the fact that groups were equated on IQ. Overall, findings suggest that a more refined classification of children with NF-1 may be helpful for tailoring academic interventions.

Influences of Neural Pathway Integrity on Children's Response to Reading Instruction

As the education field moves toward using responsiveness to intervention to identify students with disabilities, an important question is the degree to which this classification can be connected to a student's neurobiological characteristics. A few functional neuroimaging studies have reported a relationship between activation and response to instruction; however, whether a similar correlation exists with white matter (WM) is not clear. To investigate this issue, we acquired high angular resolution diffusion images from a group of first grade children who differed in their levels of responsiveness to a year-long reading intervention. Using probabilistic tractography, we calculated the strength of WM connections among nine cortical regions of interest and correlated these estimates with participants' scores on four standardized reading measures. We found eight significant correlations, four of which were connections between the insular cortex and angular gyrus. In each of the correlations, a relationship with children's response to intervention was evident.

Exploring how symptoms of attention-deficit/hyperactivity disorder are related to reading and mathematics performance: general genes, general environments

Children with attention-deficit/hyperactivity disorder (ADHD) tend to perform more poorly on tests of reading and mathematical performance than their typical peers. Quantitative genetic analyses allow for a better understanding of the etiology of ADHD and reading and mathematics outcomes, by examining their common and unique genetic and environmental influences. Analyses were conducted on a sample 271 pairs of 10-year-old monozygotic and dizygotic twins drawn from the Western Reserve Reading and Mathematics Project. In general, the results suggested that the associations among ADHD symptoms, reading outcomes, and math outcomes were influenced by both general genetic and general shared-environment factors. The analyses also suggested significant independent genetic effects for ADHD symptoms. The results imply that differing etiological factors underlie the relationships among ADHD and reading and mathematics performance. It appears that both genetic and common family or school environments link ADHD with academic performance.

Executive dysfunction among children with reading comprehension deficits

Emerging research supports the contribution of executive function (EF) to reading comprehension; however, a unique pattern has not been established for children who demonstrate comprehension difficulties despite average word recognition ability (specific reading comprehension deficit; S-RCD). To identify particular EF components on which children with S-RCD struggle, a range of EF skills was compared among 86 children, ages 10 to 14, grouped by word reading and comprehension abilities: 24 average readers, 44 with word recognition deficits (WRD), and 18 S-RCD. An exploratory principal components analysis of EF tests identified three latent factors, used in subsequent group comparisons: Planning/ Spatial Working Memory, Verbal Working Memory, and Response Inhibition. The WRD group exhibited deficits (relative to controls) on Verbal Working Memory and Inhibition factors; S-RCD children performed more poorly than controls on the Planning factor. Further analyses suggested the WRD group's poor performance on EF factors was a by-product of core deficits linked to WRD (after controlling for phonological processing, this group no longer showed EF deficits). In contrast, the S-RCD group's poor performance on the planning component remained significant after controlling for phonological processing. Findings suggest reading comprehension difficulties are linked to executive dysfunction; in particular, poor strategic planning/organizing may lead to reading comprehension problems.

Executive dysfunction among children with reading comprehension deficits

Emerging research supports the contribution of executive function (EF) to reading comprehension; however, a unique pattern has not been established for children who demonstrate comprehension difficulties despite average word recognition ability (specific reading comprehension deficit; S-RCD). To identify particular EF components on which children with S-RCD struggle, a range of EF skills was compared among 86 children, ages 10 to 14, grouped by word reading and comprehension abilities: 24 average readers, 44 with word recognition deficits (WRD), and 18 S-RCD. An exploratory principal components analysis of EF tests identified three latent factors, used in subsequent group comparisons: Planning/ Spatial Working Memory, Verbal Working Memory, and Response Inhibition. The WRD group exhibited deficits (relative to controls) on Verbal Working Memory and Inhibition factors; S-RCD children performed more poorly than controls on the Planning factor. Further analyses suggested the WRD group's poor performance on EF factors was a by-product of core deficits linked to WRD (after controlling for phonological processing, this group no longer showed EF deficits). In contrast, the S-RCD group's poor performance on the planning component remained significant after controlling for phonological processing. Findings suggest reading comprehension difficulties are linked to executive dysfunction; in particular, poor strategic planning/organizing may lead to reading comprehension problems.

White matter microstructural differences linked to left perisylvian language network in children with dyslexia

Studies of dyslexia using diffusion tensor imaging (DTI) have reported fractional anisotropy (FA) differences in left inferior frontal gyrus (LIFG) and left temporo-parietal white matter, suggesting that impaired reading is associated with atypical white matter microstructure in these regions. These anomalies might reflect abnormalities in the left perisylvian language network, long implicated in dyslexia. While DTI investigations frequently report analyses on multiple tensor-derived measures (e.g., FA, orientation, tractography), it is uncommon to integrate analyses to examine the relationships between atypical findings. For the present study, semi-automated techniques were applied to DTI data in an integrated fashion to examine white matter microstructure in 14 children with dyslexia and 17 typically developing readers (ages 7-16 years). Correlations of DTI metrics (FA and fiber orientation) to reading skill (accuracy and speed) and to probabilistic tractography maps of the left perisylvian language tracts were examined. Consistent with previous reports, our findings suggest FA decreases in dyslexia in LIFG and left temporo-parietal white matter. The LIFG FA finding overlaps an area showing differences in fiber orientation in an anterior left perisylvian language pathway. Additionally, a positive correlation of FA to reading speed was found in a posterior circuit previously associated with activation on functional imaging during reading tasks. Overall, integrating results from several complementary semi-automated analyses reveals evidence linking atypical white matter microstructure in dyslexia to atypical fiber orientation in circuits implicated in reading including the left perisylvian language network.

Environmental influences on the longitudinal covariance of expressive vocabulary: measuring the home literacy environment in a genetically sensitive design

BACKGROUND

Despite the well-replicated relationship between the home literacy environment and expressive vocabulary, few studies have examined the extent to which the home literacy environment is associated with the development of early vocabulary ability in the context of genetic influences. This study examined the influence of the home literacy environment on the longitudinal covariance of expressive vocabulary within a genetically sensitive design.

METHODS

Participants were drawn from the Western Reserve Reading Project, a longitudinal twin project of 314 twin pairs based in Ohio. Twins were assessed via three annual home visits during early elementary school; expressive vocabulary was measured via the Boston Naming Test (BNT), and the Home Literacy Environment (HLE) was assessed using mothers' report.

RESULTS

The heritability of the BNT was moderate and significant at each measurement occasion, h(2) = .29-.49, as were the estimates of the shared environment, c(2) = .27-.39. HLE accounted for between 6-10% of the total variance in each year of vocabulary assessment. Furthermore, 7-9% of the total variance of the stability over time in BNT was accounted for by covariance in the home literacy environment.

CONCLUSIONS

These results indicate that aspects of the home literacy environment, as reported by mothers, account for some of the shared environmental variance associated with expressive vocabulary in school aged children.

The contribution of executive skills to reading comprehension

Although word recognition deficits (WRD) are a known cause of reading comprehension deficits (RCD), other contributions to RCD, including executive function (EF), have not been fully explored. We examined the contribution of EF (working memory and planning), along with attention, decoding, fluency, and vocabulary to reading comprehension in 60 children (including 16 WRD and 10 RCD), ages 9-15 years. After controlling for commonly accepted contributors to reading comprehension (i.e., attention, decoding skills, fluency, and vocabulary), EF continued to make a significant contribution to reading comprehension but not to word recognition skills. These findings highlight the need for consideration of the role of EF in RCD.

A dual DTI approach to analyzing white matter in children with dyslexia

Using voxel-based (VBA) and region-of-interest (ROI) diffusion tensor imaging (DTI) analyses, we examined white matter (WM) organization in seven children with dyslexia and six age-matched controls. Both methods demonstrated reduced fractional anisotropy (FA) in the left superior longitudinal fasciculus (SLF) and abnormal orientation in the right SLF in dyslexics. Application of this complementary dual DTI approach to dyslexia, which included novel analyses of fiber orientation, demonstrates its usefulness for analyzing mild and complex WM abnormalities.

Effects of fluency, oral language, and executive function on reading comprehension performance

Reading disability (RD) typically consists of deficits in word reading accuracy and/or reading comprehension. While it is well known that word reading accuracy deficits lead to comprehension deficits (general reading disability, GRD), less is understood about neuropsychological profiles of children who exhibit adequate word reading accuracy but nevertheless develop specific reading comprehension deficits (S-RCD). Establishing the underlying neuropsychological processes associated with different RD types is essential for ultimately understanding core neurobiological bases of reading comprehension. To this end, the present study investigated isolated and contextual word fluency, oral language, and executive function on reading comprehension performance in 56 9- to 14-year-old children [21 typically developing (TD), 18 GRD, and 17 S-RCD]. Results indicated that TD and S-RCD participants read isolated words at a faster rate than participants with GRD; however, both RD groups had contextual word fluency and oral language weaknesses. Additionally, S-RCD participants showed prominent weaknesses in executive function. Implications for understanding the neuropsychological bases for reading comprehension are discussed.

Response variability in rapid automatized naming predicts reading comprehension

A total of 37 children ages 8 to 14 years, screened for word-reading difficulties (23 with attention-deficit/hyperactivity disorder, ADHD; 14 controls) completed oral reading and rapid automatized naming (RAN) tests. RAN trials were segmented into pause and articulation time and intraindividual variability. There were no group differences on reading or RAN variables. Color- and letter-naming pause times and number-naming articulation time were significant predictors of reading fluency. In contrast, number and letter pause variability were predictors of comprehension. Results support analysis of subcomponents of RAN and add to literature emphasizing intraindividual variability as a marker for response preparation, which has relevance to reading comprehension.

Developmental sex differences in basic visuospatial processing: differences in strategy use?

Functional neuroimaging studies investigating sex differences in visuospatial processing traditionally focus on mental rotation tasks in adults, as it is a consistently robust finding, with a limited number of studies examining tasks tapping visuospatial skills at a more basic level. Furthermore, fewer studies have examined this issue in conjunction with investigating whether differences exist in younger populations. Therefore, functional neuroimaging was used to examine whether sex-based differences exist and/or develop during childhood. Thirty-two participants, matched on performance, participated in this study. Overall, both groups showed overlapping activation in bilateral superior parietal lobe, extrastriate cortex, and cerebellum; differences between the sexes showed that males had significantly greater activation in right lingual gyrus and cerebellum. Formal comparisons between age groups revealed that older males show engagement of left hemisphere regions, while females show greater bilateral (R>L) engagement of regions traditionally associated with visuospatial processing. Together, these results suggest that older males, as compared to younger males, may engage regions that are associated with a visuomotor network, whereas females utilize areas indicated in spatial attention and working memory. Furthermore, these results could also suggest that there may be differences in strategy use that are evident early on and may continue to develop over time evident by differential engagement of networks associated with visuospatial processing. Our data provide evidence for sex-based differences in the neural basis of visuospatial processing.

Functional MRI of sentence comprehension in children with dyslexia: beyond word recognition

Sentence comprehension (SC) studies in typical and impaired readers suggest that reading for meaning involves more extensive brain activation than reading isolated words. Thus far, no reading disability/dyslexia (RD) studies have directly controlled for the word recognition (WR) components of SC tasks, which is central for understanding comprehension processes beyond WR. This experiment compared SC to WR in 29, 9-14 year olds (15 typical and 14 impaired readers). The SC-WR contrast for each group showed activation in left inferior frontal and extrastriate regions, but the RD group showed significantly more activation than Controls in areas associated with linguistic processing (left middle/superior temporal gyri), and attention and response selection (bilateral insula, right cingulate gyrus, right superior frontal gyrus, and right parietal lobe). Further analyses revealed this overactivation was driven by the RD group's response to incongruous sentences. Correlations with out-of-scanner measures showed that better word- and text-level reading fluency was associated with greater left occipitotemporal activation, whereas worse performance on WR, fluency, and comprehension (reading and oral) were associated with greater right hemisphere activation in a variety of areas, including supramarginal and superior temporal gyri. Results provide initial foundations for understanding the neurobiological correlates of higher-level processes associated with reading comprehension.

Effects of gender and age on motor exam in typically developing children

Few studies have contrasted performance of typically developing boys and girls on standardized motor assessment. In the present study, developmental status of the motor system was assessed in 144 typically developing children (72 boys, 72 girls, ages 7-14), using the Physical and Neurological Examination for Subtle Signs (PANESS, Denckla, 1985). Four summary variables were examined: (1) Gaits and Stations, (2) Overflow, (3) Dysrythmia, and (4) Timed Movements. For most variables, gender differences were not significant; however significant gender effects were observed for some subtle signs (involuntary movements), gaits and stations, and timed patterned movements. In all instances, girls showed fewer subtle signs and were faster and more proficient than boys. Significant age-related changes were observed for some subtle signs (dysrythmia and overflow), and for timed movements. In contrast, by age 7, many of the skills assessed by the PANESS have reached "adult" level in typically developing children. Motor development appears to follow a different developmental course in girls than in boys; separate gender and age norms should be used in clinical assessment of motor function in children.

Visuospatial processing in children with neurofibromatosis type 1

Neuroimaging studies investigating the neural network of visuospatial processing have revealed a right hemisphere network of activation including inferior parietal lobe, dorsolateral prefrontal cortex, and extrastriate regions. Impaired visuospatial processing, indicated by the Judgment of Line Orientation (JLO), is commonly seen in individuals with neurofibromatosis type 1 (NF-1). Nevertheless, few studies have examined the neural activity associated with visuospatial processing in NF-1, in particular, during a JLO task. This study used functional neuroimaging to explore differences in volume of activation in predefined regions of interest between 13 individuals with NF-1 and 13 controls while performing an analogue JLO task. We hypothesized that participants with NF-1 would show anomalous right hemisphere activation and therefore would recruit regions within the left hemisphere to complete the task. Multivariate analyses of variance were used to test for differences between groups in frontal, temporal, parietal, and occipital regions. Results indicate that, as predicted, controls utilized various right hemisphere regions to complete the task, while the NF-1 group tended to recruit left hemisphere regions. These results suggest that the NF-1 group has an inefficient right hemisphere network. An additional unexpected finding was that the NF-1 group showed decreased volume of activation in primary visual cortex (BA 17). Future studies are needed to examine whether the decrease in primary visual cortex is related to a deficit in basic visual processing; findings could ultimately lead to a greater understanding of the nature of deficits in NF-1 and have implications for remediation.

Construct Validity of Parent Ratings of Inhibitory Control

Recent literature has emphasized the need to examine executive functions (EF) in children using multiple sources, including both parent rating and performance-based measures. Computerized Go/No-Go tests, including commercially available continuous performance tests (CPTs), represent one of the most commonly used methods of assessing inhibitory control - a variable central to the executive function construct. We examined the relationship between parent ratings of inhibitory control and CPT performance in two mixed clinical samples. Experiment 1 examined 109 children ages 6-18 using the Behavior Rating Inventory of Executive Function (BRIEF; Gioia, Isquith, Guy, & Kenworthy, 2000) and the Conners' CPT-II (Conners, 2000). In this sample, ratings on the BRIEF Inhibit scale (mean T-score = 62.3) were significantly higher than the CPT-II commissions score (mean T-score = 50.7; p < .0001); and the BRIEF and CPT-II scores were not highly correlated (r = - .12). Experiment 2 examined a sample of 131 children ages 7-18 using the BRIEF and the Tests of Variables of Attention (TOVA; Greenberg, 1996). In this sample, parent ratings on the BRIEF Inhibit scale (mean T-score = 56.8) were similar to TOVA commissions scores (mean T-score = 58.6; p = .33), although still poorly correlated (r = -.02). Factor analyses exploring covariance between BRIEF scales CPT-II variables (Experiment 1) and between BRIEF and TOVA (Experiment 2) yielded similar findings. In both experiments, all eight BRIEF scales loaded on a single factor, with no overlap with either the CPT-II or the TOVA. In mixed outpatient clinical samples, the BRIEF appears to measure different elements of inhibitory control than those assessed by computerized continuous performance tests.

Left-right differences on timed motor examination in children

Age-related change in the difference between left- and right-side speed on motor examination may be an important indicator of maturation. Cortical maturation and myelination of the corpus callosum are considered to be related to increased bilateral skill and speed on timed motor tasks. We compared left minus right foot, hand, and finger speed differences using the Revised Physical and Neurological Assessment for Subtle Signs (PANESS; Denckla, 1985); examining 130 typically developing right-handed children (65 boys, 65 girls) ages 7-14. Timed tasks included right and left sets of 20 toe taps, 10 toe-heel alternation sequences, 20 hand pats, 10 hand pronate-supinate sets, 20 finger taps, and 5 sequences of each finger-to-thumb apposition. For each individual, six difference scores between left- and right-sided speeded performances of timed motor tasks were analyzed. Left-right differences decreased significantly with age on toe tapping, heel-toe alternations, hand pronation-supination, finger repetition, and finger sequencing. There were significant gender effects for heel-toe sequences (boys showing a greater left-right difference than girls), and a significant interaction between age and gender for hand pronation-supination, such that the magnitude of the left-right difference was similar for younger, compared with older girls, while the difference was significantly larger for younger, compared to older boys. Speed of performing right and left timed motor tasks equalizes with development; for some tasks, the equalization occurs earlier in girls than in boys.

Sex differences in cerebral laterality of language and visuospatial processing

Sex differences on language and visuospatial tasks are of great interest, with differences in hemispheric laterality hypothesized to exist between males and females. Some functional imaging studies examining sex differences have shown that males are more left lateralized on language tasks and females are more right lateralized on visuospatial tasks; however, findings are inconsistent. Here we used functional magnetic resonance imaging to study thirty participants, matched on task performance, during phonological and visuospatial tasks. For each task, region-of-interest analyses were used to test differences in cerebral laterality. Results indicate that lateralization differences exist, with males more left lateralized during the phonological task and showing greater bilateral activity during the visuospatial task, whereas females showed greater bilateral activity during the phonological task and were more right lateralized during the visuospatial task. Our data provide clear evidence for differences in laterality between males and females when processing language versus visuospatial information.

Cognitive profile of neurofibromatosis type 1

General consensus has yet to be reached with regard to the exact cognitive profile of children with neurofibromatosis type 1 (NF1). The current overview seeks to provide a more comprehensive review of the literature by examining studies that have specifically compared individuals with NF1 to siblings, controls, and/or norms. We also examined results of studies that compared individuals with NF1 with various manifestations to each other. Consistent with previous reviews, no clear cognitive profile emerged; however, greater insight into patterns was obtained. Additionally, future directions for research on NF1 were suggested.

Subtle executive impairment in children with autism and children with ADHD

BACKGROUND

The executive functions of inhibition, planning, flexible shifting of actions, and working memory are commonly reported to be impaired in neurodevelopmental disorders.

METHOD

We compared these abilities in children (8-12 years) with high functioning autism (HFA, n = 17), attention deficit-hyperactivity disorder (ADHD, n = 21) and healthy controls (n = 32). Response inhibition was assessed using the Stroop Color and Word Test (Golden, 1978). Problem solving, set-shifting, and nonverbal memory were assessed using three tasks, respectively, from the CANTAB (Cambridge Cognition, 1996): the Stockings of Cambridge task; the Intra-Dimensional/Extra-Dimensional set-shifting task; and the Spatial Working Memory task (SWM) with tokens hidden behind 3, 4, 6, and 8 boxes.

RESULTS

There were no group differences on the response inhibition, planning, or set-shifting tasks. On the SWM task, children with HFA made significantly more between-search errors compared with controls on both the most difficult problems (8-box) and on the mid-difficulty problems (6-box); however, children with ADHD made significantly more errors compared to controls on the most difficult (8-box) problems only.

CONCLUSION

Our findings suggest that spatial working memory is impaired in both ADHD and HFA, and more severely in the latter. More detailed investigation is needed to examine the mechanisms that differentially impair spatial working memory, but on this set of tasks there appears to be sparing of other executive functions in these neuropsychiatric developmental disorders.

Differential components of sentence comprehension: beyond single word reading and memory

A number of studies have used functional neuroimaging to examine the neural mechanisms of sentence comprehension; however, few fMRI studies have examined activation patterns associated with sentence comprehension after accounting for activation attributable to single-word-level tasks important for sentence comprehension. To investigate the patterns of activation associated with sentence comprehension after controlling for single word reading and maintaining single words in memory, 20 unimpaired adult readers completed a block design paradigm which included sentence comprehension, single word reading, and short-term memory (for words) tasks. Results indicated that, regardless of the aspect of sentence comprehension being controlled for, activation was observed in bilateral temporal lobes (left > right) as well as bilateral occipital lobes and middle frontal gyri. Additional findings showed that bilateral superior parietal lobe activation was greatest for short-term memory for words, while left anterior inferior frontal gyri activation (centered around Brodmann's area 47) was greatest for single word reading. Results suggest that temporal cortex (left > right) is a core region important for sentence comprehension beyond the short-term memory and semantic requirements inherent in processing sentences.

Evidence for unexpected weaknesses in learning in children with attention-deficit/hyperactivity disorder without reading disabilities

This study examined the mechanisms underlying verbal learning in children with and without attention-deficit/hyperactivity disorder (ADHD), none of whom had reading disabilities. Children with ADHD were compared to typically developing children on both process and product scores from the California Verbal Learning Test for Children. The findings indicated that children with ADHD initially learned the same number of words as controls but showed weaknesses recalling the words after delays, suggesting that children with ADHD are less efficient learners. Regardless of ADHD status, boys and girls performed differently. Boys used semantic clustering less frequently and recalled fewer words from the middle region of the list than girls; girls also outperformed boys in terms of overall performance, despite lower verbal IQ scores. These findings show that children with ADHD can exhibit unexpected weaknesses in learning even without a formal learning disability. Gender differences in verbal learning are also illustrated.

Megalencephaly in NF1: predominantly white matter contribution and mitigation by ADHD

BACKGROUND

Megalencephaly is a frequent CNS manifestation in neurofibromatosis type 1 (NF1); however, its tissue composition, modification by attention deficit hyperactivity disorder (ADHD), and relationship with unidentified bright objects (UBO) remain controversial.

METHODS

Eighteen male patients with NF1, seven of whom had ADHD (NF1+ADHD), were compared with 18 age- and sex-matched controls in terms of MRI-, Talairach-based brain, cerebral, lobar, and sublobar gray and white matter volumes. Twelve subjects with NF1 had UBO in the centrencephalic region, whereas six had no UBO or exclusively infratentorial lesions.

RESULTS

Patients with NF1 without ADHD (NF1-pure) had the largest total cerebral, gray, and white matter volumes with larger parietal/somatosensory white matter volumes than controls, particularly if UBO were present in the basal ganglia. All subjects with NF1 (including NF1+ADHD) had larger total and frontal white matter volumes than controls. Smaller frontal/right prefrontal gray matter volumes were found in NF1+ADHD when compared with NF1-pure patients.

CONCLUSIONS

The increase in frontal and parietal white matter volumes in male patients with NF1, including the preferential centrencephalic distribution, supports the hypothesis that NF1's white matter pathology encompasses but is not limited to visible UBO. Male patients with NF1+ADHD, as compared with NF1-pure patients, showed frontal reductions that are largely consistent with those found in idiopathic ADHD.

Validity of the behavior rating inventory of executive function in children with ADHD and/or Tourette syndrome

The dynamic, multidimensional nature of executive function (EF), thought to be characteristically impaired in those with attention deficit hyperactivity disorder (ADHD), has been challenging to operationalize and assess in a clinical setting [Barkley, R. A. (1997). ADHD and the nature of self-control. New York: Guilford Press.]. Gioia, Isquith, Guy, and Kenworthy [Gioia, G. A., Isquith, P. K., Guy, S. C., & Kenworthy, L. (2000) Behavior Rating Inventory of Executive Function. Odessa, FL: Psychological Assessment Resources.] developed the Behavior Rating Inventory of Executive Function (BRIEF) to address these concerns. In order to provide concurrent validity information on the BRIEF, parents of 76 children (ADHD=18; Tourette syndrome (TS)=21; TS+ADHD=17; controls=20) completed the BRIEF, additional behavior rating scales and interviews, measures of psychoeducational (PE) competence, and performance-based measures of EF. Both ADHD and TS+ADHD groups were rated as more impaired (P<.0001) than the other groups on the five primary BRIEF indices. BRIEF index scores showed no significant correlation with performance-based EF or PE measures, with the exception of math achievement; however, the BRIEF showed a strong relationship with interviews and other parent rating measures of behaviors seen in ADHD. Future attempts to validate the BRIEF should focus on differences within subtypes of ADHD (e.g., inattentive, combined subtypes), and separating ADHD from other clinical groups in which EF is reported to be a problem.

Validity of the behavior rating inventory of executive function in children with ADHD and/or Tourette syndrome

The dynamic, multidimensional nature of executive function (EF), thought to be characteristically impaired in those with attention deficit hyperactivity disorder (ADHD), has been challenging to operationalize and assess in a clinical setting [Barkley, R. A. (1997). ADHD and the nature of self-control. New York: Guilford Press.]. Gioia, Isquith, Guy, and Kenworthy [Gioia, G. A., Isquith, P. K., Guy, S. C., & Kenworthy, L. (2000) Behavior Rating Inventory of Executive Function. Odessa, FL: Psychological Assessment Resources.] developed the Behavior Rating Inventory of Executive Function (BRIEF) to address these concerns. In order to provide concurrent validity information on the BRIEF, parents of 76 children (ADHD=18; Tourette syndrome (TS)=21; TS+ADHD=17; controls=20) completed the BRIEF, additional behavior rating scales and interviews, measures of psychoeducational (PE) competence, and performance-based measures of EF. Both ADHD and TS+ADHD groups were rated as more impaired (P<.0001) than the other groups on the five primary BRIEF indices. BRIEF index scores showed no significant correlation with performance-based EF or PE measures, with the exception of math achievement; however, the BRIEF showed a strong relationship with interviews and other parent rating measures of behaviors seen in ADHD. Future attempts to validate the BRIEF should focus on differences within subtypes of ADHD (e.g., inattentive, combined subtypes), and separating ADHD from other clinical groups in which EF is reported to be a problem.

Growth curve analyses of neuropsychological profiles in children with neurofibromatosis type 1: specific cognitive tests remain "spared" and "impaired" over time

Cognitive deficits in neurofibromatosis Type 1 (NF-1) have been documented in both the verbal and visuospatial domains. Previous investigations from our laboratory have determined a specific pattern of "spared" (Picture Arrangement, Picture Completion, and Rapid Automatized Naming) and "impaired" (Judgment of Line Orientation, Vocabulary, and Block Design) performance on cognitive measures in this population when compared to sibling-matched controls in pairwise designs. Growth curve analyses were conducted on these repeated measures in 19 patients with NF-1 and their siblings to investigate the longitudinal course and growth pattern of these spared and impaired measures. Results indicated that over time children with NF-1 do not catch up to their siblings on impaired measures, and they continue to perform similarly to their siblings on the spared measures. With respect to growth rates, on average across the 6 cognitive measures there was no significant difference between the groups. However, the variation among families for level of performance was estimated to be larger than variation among siblings within a family for 2 out of 6 cognitive measures (i.e., providing for these 2, Vocabulary and Rapid Automatized Naming, evidence of substantial familial correlation), suggesting that there is need to consider NF-1 associated deficits within a familial context.

Effects of IQ on executive function measures in children with ADHD

The present study compared children with Attention-Deficit Hyperactivity Disorder (ADHD) and controls on a selected set of clinical measures of executive function (EF). A total of 92 children (51 ADHD, 41 control), ages 6-16, completed measures chosen from a larger neuropsychological battery to illustrate diverse components of the EF construct (planning, inhibitory control, response preparation, memory search). The selected measures were moderately correlated with one another, and moderately correlated with IQ. After controlling for age, sex, presence of learning disability (LD), ADHD, and IQ test version, Full Scale IQ was significantly related to four of the five selected EF measures. A second analysis showed group differences on the EF measures at different IQ levels. After covarying for age, there was a significant multivariate effect for IQ level (average, high average, superior) and a significant multivariate interaction between group (ADHD vs. control) and IQ level. Three of the five selected EF measures showed significant univariate group effects (controls performing better than ADHD) at the average IQ level; however, there were no significant group differences between children with ADHD and controls at high average or superior IQ levels. These results suggest that clinical measures of EF may differ among children with ADHD and controls at average IQ levels, but there is poorer discriminatory power for these measures among children with above average IQ.

Disproportionate increases of white matter in right frontal lobe in Tourette syndrome

OBJECTIVE

Based on previous findings implicating abnormalities of cortico-striatal-thalamo-cortical circuitry in Tourette syndrome (TS), the authors performed a volumetric analysis of frontal and nonfrontal tissue (gray + white matter) in boys with TS, with and without attention deficit hyperactivity disorder (ADHD).

METHODS

Frontal and nonfrontal gray and white matter compartment volumes, obtained by a MRI protocol, were analyzed with a 2 x 2 factorial multivariate analysis of variance approach for associations with a TS or ADHD factor in 11 boys with TS only, 14 with TS + ADHD, 12 with ADHD only, and 26 healthy boys.

RESULTS

In subjects with TS, the right frontal lobe showed a larger proportion of white matter. In addition, results were consistent with previous reports of reduced frontal lobe volumes associated with ADHD. Our analyses suggested these reductions to be mainly the consequence of smaller gray matter volumes, particularly on the left.

CONCLUSIONS

These findings, suggesting the volumetric composition of frontal lobe tissue to be different in TS, support the hypothesis proposing frontostriatal pathway involvement in the pathophysiology of the disorder. Differences in composition of right frontal lobe attributable to white matter do not definitively implicate the hypothesized fiber pathways; however, considered in the context of the unilateral directionality of frontal-striatal circuitry, these results suggest the white matter connections as one explanation for basal ganglia anomalies (loss of normal left > right asymmetry) in TS.

Oculomotor abnormalities in attention deficit hyperactivity disorder: a preliminary study

BACKGROUND

Prevailing hypotheses suggest that attention deficit hyperactivity disorder (ADHD) is secondary to dysfunction of motor intentional systems mediated by prefrontal circuitry. Oculomotor paradigms provide a mechanism for examining and localizing dysfunction at the interface between movement and cognition.

OBJECTIVE

Three different saccade tasks (reflexive or prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and the execution of eye movements, including motor response preparation, response inhibition, and working memory.

METHODS

The study included 19 children with ADHD, divided into two groups: a group of 8 children on methylphenidate at the time of testing and a group of 11 children not taking any psychoactive medication. Results from the two groups were compared with those from 25 age- and gender-matched normal control children.

RESULTS

Both groups of children with ADHD made significantly more directional errors than did controls on the antisaccade task and significantly more anticipatory errors than did controls on the memory-guided saccade task, findings that are consistent with deficits in response inhibition. There were no significant differences in prosaccade latency, although unmedicated children with ADHD showed significantly greater variability in latency on the prosaccade task than did controls. On the memory-guided saccade task there were no significant differences in saccade accuracy; however, unmedicated children with ADHD showed longer saccade latency than did either controls or medicated children with ADHD.

CONCLUSIONS

Oculomotor findings suggest that deficits in prefrontal functions, in particular response inhibition, contribute to behavioral abnormalities observed in ADHD. Findings also suggest that the administration of methylphenidate is associated with improvements in the consistency of motor response. Although there were no observed improvements in response inhibition with methylphenidate, conclusions await a design in which subjects complete testing both on and off medication.

The association of neurofibromatosis type 1 and attention deficit hyperactivity disorder

Some research and clinical observations have linked Neurofibromatosis Type 1 (NF-1) and Attention Deficit Hyperactivity Disorder (ADHD). In order to investigate whether ADHD is part of the phenotype of NF-1 or is a separate, unrelated disorder within families, we compared the ADHD status of children affected with NF-1 to that of their unaffected-NF-1 siblings and to that of their biological parents. Results of matched-pair analyses were calculated and revealed a significant with-in pair discordance, when comparing children with NF-1 and their siblings and when comparing children with NF-1 and their biological parents (in families with a sporadic, non-familial NF-1 child). These findings suggest that ADHD may occur as a component of the NF-1 phenotype.

Judgment of duration in individuals with ataxia-telangiectasia

Several clinical investigations with adults suggest that the cerebellum may be critical for judgment of explicit time intervals; however, little work has been done in populations with lesions of the cerebellum acquired during development. We evaluated 17 individuals with ataxia-telangiectasia (AT), an autosomal recessive disorder with on-set in early childhood characterized by diffuse, almost selective, degeneration of the cerebellar cortex, and 21 normal controls, matched for age. Because patients with AT have motor impairment, verbal IQ (VIQ) was used to estimate intelligence; VIQ was significantly lower in the group with AT (p < .0001). Participants were tested using a test of judgment of duration that has been found to be impaired in adults with cerebellar lesions and a contrasting auditory control task (not impaired in adults with cerebellar lesions) involving judgment of pitch. After statistically controlling for VIQ, the 2 groups did not differ significantly on judgment of pitch, but those with AT performed significantly worse than controls on judgment of duration (p = .01). Children and adolescents with AT show deficits in judgment of duration but not of pitch, suggesting that the cerebellum may be critical for judgment of explicit time intervals at all ages.