The contribution of novel brain imaging techniques to understanding the neurobiology of mental retardation and developmental disabilities

Studying the biological mechanisms underlying mental retardation and developmental disabilities (MR/DD) is a very complex task. This is due to the wide heterogeneity of etiologies and pathways that lead to MR/DD. Breakthroughs in genetics and molecular biology and the development of sophisticated brain imaging techniques during the last decades have facilitated the emergence of a field called Behavioral Neurogenetics. Behavioral Neurogenetics focuses on studying genetic diseases with known etiologies that are manifested by unique cognitive and behavioral phenotypes. In this review, we describe the principles of magnetic resonance imaging (MRI) techniques, including structural MRI, functional MRI, and diffusion tensor imaging (DTI), and how they are implemented in the study of Williams (WS), velocardiofacial (VCFS), and fragile X (FXS) syndromes. From WS we learn that dorsal stream abnormalities can be associated with visuospatial deficits; VCFS is a model for exploring the molecular and brain pathways that lead to psychiatric disorders for which subjects with MR/DD are at increased risk; and finally, findings from multimodal imaging techniques show that aberrant frontal-striatal connections are implicated in the executive function and attentional deficits of subjects with FXS. By deciphering the molecular pathways and brain structure and function associated with cognitive deficits, we will gain a better understanding of the pathophysiology of MR/DD, which will eventually make possible more specific treatments for this population.     

Abnormal optokinetic and perceptual span parameters in cerebellar-vestibular dysfunction and learning disabilities or dyslexia

To measure the ocular fixation and sequential scanning dysfunction assumed responsible for the visual reading symptoms which characterize dyslexia or learning disabilities, an optokinetically based tracking method was devised. This method quantitatively demonstrated significantly reduced fixation, tracking, and perceptual or visual-span scores as well as "movement illusions" for 70 cerebellar-vestibular dysfunctioning persons with learning disabilities vs 70 controls. Such data tended to validate the hypothesis that cerebellar-vestibular-determined fixation and tracking mechanisms predispose dyslexic or learning disabled individuals to visual reading disorders. Moreover, a newly revised method is presented which may prove useful in rapidly screening and diagnosing cerebellar-vestibular-determined reading and learning disorders from those of other origins. Additional independent studies using significantly larger samples and asymptomatic or "normal" controls are required for further validation and development of the method.     

干预-应答模式鉴别学习障碍的有效性及其调节因素:20年研究的元分析

本研究采用元分析方法探讨在学习障碍的鉴别中兴起的干预-应答（Response to Intervention,RTI）模式鉴别学习障碍内部亚组的有效性及其调节因素。通过系统检索1996-2015年的文献,获得了34项研究,包括6127名学生的45个样本、261个效应值。元分析结果表明,RTI模式可有效区分学习障碍风险儿童的内部亚组,对干预无应答和有应答的学生在学业成就、认知技能、行为等多方面存在系统、显著和持久的差异,但仍存在个体应答状态的进一步分化。RTI模式对于学习障碍风险儿童内部变异的区分效果受到干预对象、干预层次、干预时间、应答指标选择、测量方法和切分点等因素的影响。本元分析结果不仅为认识RTI模式鉴别学习障碍的有效性提供了进一步证据,更重要的是通过系列调节效应分析,为合理实施RTI模式鉴别学习障碍提供了直接依据。     

A Better Look at Intelligence

The Planning, Attention, Simultaneous, and Successive (PASS) model is offered as an alternative to the unidimensional conceptualization of intelligence as a general ability. The unidimensional conceptualization has not helped researchers and clinicians understand variations of cognitive functions within special populations such as individuals with learning disabilities, disorders of attention, or mental retardation. Neither has this conceptualization aided in program planning for these individuals. PASS is a model of cognitive function based on contemporary research in both cognition and neuropsychology and provides a theory for both assessment and intervention. This article reviews concepts and examples of PASS theory and its application to reading disabilities and mental retardation. For example, the article links dyslexia with a deficit in successive processing. It also identifies the major difficulties of individuals with Down syndrome in phonological memory and articulation. Further research on successive processing, and planning as it relates to language, is suggested.     

COGNITIVE PROFILES OF READING-DISABLED CHILDREN:

Abstract— A comprehensive cognitive appraisal of elementary school children with learning disabilities showed that within the language sphere, deficits associated with reading disability are selective. Phonological deficits consistently accompany reading problems whether they occur in relatively pure form or in the presence of coexisting attention deficit or arithmetic disability. Although reading-disabled children were also deficient in production of morphologically related forms, this difficulty stemmed in large part from the same weakness in the phonological component that underlies reading disability. In contrast, tests of syntactic knowledge did not distinguish reading-disabled children from those with other cognitive disabilities, nor from normal children after covarying for intelligence.     

Neuropsychological status of French children with developmental dyslexia and/or developmental coordination disorder: Are both necessarily worse than one?

Developmental dyslexia (DD) and developmental coordination disorder (DCD) co-occur frequently, raising the underlying question of shared etiological bases. We investigated the cognitive profile of children with DD, children with DCD, and children with the dual association (DD + DCD) to determine the inherent characteristics of each disorder and explore the possible additional impact of co-morbidity on intellectual, attentional, and psychosocial functioning. The participants were 8- to 12-year-olds (20 DD, 22 DCD, and 23 DD + DCD). Cognitive abilities were assessed by the Wechsler Intelligence Scale for Children – Fourth Edition (WISC-IV) and the Continuous Performance Test – Second Edition (CPT-II) and behavioral impairments were evaluated by the Child Behavior Checklist (CBCL). No differences were found between the three groups on attention testing (CPT-II) or psychosocial characteristics (CBCL), but a higher percentage of DD + DCD children had pathological scores on psychosocial scales. Significant between-group differences were observed on Processing Speed Index scores and the block design and symbol search subtests, where DD children fared better than DCD children. No significant differences were evident between the co-morbid vs. the pure groups. Our results clearly show significant differences between children with DD only and children with DCD only. In particular, visuo-spatial disabilities and heterogeneity of intellectual profile seem to be good markers of DCD. However, it should be noted that despite these distinct and separate characteristics, a common cognitive profile (weaknesses and strengths) is likely shared by both neurodevelopmental disorders. Surprisingly, concerning co-morbidity, DD + DCD association is not associated with a decrease in intellectual or attentional capacities.     

阅读发展相关的认知技能：汉语和英语的比较

对英语和汉语阅读获得所需要的认知技能及发展性阅读障碍儿童认知缺陷的研究进行了回顾。分析表明阅读发展所需认知资源表现出了跨语言的一致性,都要求有充足的学习与记忆能力和正常的视觉正字法技能,语音和语义知识表征足够精细;阅读障碍儿童的主要认知缺陷也表现出了跨文字的一致性,都包括语音缺陷和一般的学习与记忆问题。然而儿童所面临的语言文字特性会影响到阅读技能获得的难易和发展性阅读障碍的表现     

我国近十年来汉语阅读障碍研究回顾与展望

发展性阅读障碍（developmentaldyslexia,DD）是一种严重的学习障碍。文章回顾了l996~2006年间中国内地作者发表的有关汉语DD的实证性文章,发现我国学者近十年来对汉语DD的研究主要包括DD的诊断筛选、亚型分析、认知特点和认知神经机制研究、教育干预等几个方面。文章同时探讨了现有研究中存在的不足,如诊断标准不统一;研究领域比较狭窄;缺乏有效的干预模式和实证研究等,最后提出了研究的发展趋势和未来研究方向     

Genetics and educational psychology

Background: Molecular genetics, one of the most energetic and exciting areas of science, is slowly but surely coming to educational psychology. Aims: We review recent molecular genetic research on learning disabilities as a sign of things to come in educational psychology. We also consider some misconceptions about genetics that have slowed the acceptance of genetics in educational psychology. Samples: Diverse samples of children with learning disabilities have been studied, primarily in the UK and the USA. Methods: Linkage analysis can detect genes that have large effects on learning disabilities. Association analysis can detect genes of much smaller effect size, which is important because common disorders such as learning disabilities are likely to be influenced by many genes as well as by many environmental factors. Results: For reading disability, replicated linkages have been identified on chromosomes 6, 15 and 18. A gene responsible for a rare type of language impairment has recently been identified. For common language impairment, linkages on chromosomes 16 and 19 have recently been reported. More than 200 genetic disorders, most extremely rare, include mental retardation among their symptoms, and chromosomal abnormalities are a major cause of mental retardation. Conclusions: Although finding specific genes associated with learning disabilities is unlikely to have much of a direct application for teachers in the classroom, such findings will have far‐reaching implications for diagnosis, treatment and prevention of learning disabilities and for research in educational psychology. Educational psychology has been slower to accept evidence for the importance of genetics than other areas of psychology in part because of misconceptions about what it means to say that genetics is important for common complex disorders such as learning disabilities.     

The developmental course of processing speed in children with and without learning disabilities

This study contrasted the development of processing speed in children with and without learning disabilities. We examined whether the same global mechanism presumed to be responsible for the normal developmental improvement in processing speed might also be associated with the processing speed deficiencies observed in children with learning impairments. One hundred and twenty-two children with learning disabilities in reading and/or math and 206 non-disabled community controls participated. There were no differences in relation of age to the development of processing speed for children with and without learning disabilities. We interpreted these results as suggesting that the underlying etiologies for the normal developmental change in processing speed and for the relative deficiencies in processing speed seen among children with learning disabilities were different.     

Effective learning and retention of braille letter tactile discrimination skills in children with developmental dyslexia

Children with developmental dyslexia (DD) may differ from typical readers in aspects other than reading. The notion of a general deficit in the ability to acquire and retain procedural (‘how to’) knowledge as long‐term procedural memory has been proposed. Here, we compared the ability of elementary school children, with and without reading difficulties (DD, typical readers), to improve their tactile discrimination with practice and tested the children's ability to retain the gains. Forty 10–11‐year‐olds practiced the tactile discrimination of four braille letters, presented as pairs, while blindfolded. In a trial, participants were asked to report whether the target stimuli were identical or different from each other. The structured training session consisted of six blocks of 16 trials each. Performance was re‐tested at 24 hours and two weeks post‐training. Both groups improved in speed and in accuracy. In session 1, children with DD started as significantly less accurate and were slower than the typical readers but showed rapid learning and successfully closed the gap. Only two children with DD failed to benefit from training and were not included in subsequent data analyses. At 24 hours post‐training both groups showed effective retention of the gains in speed and accuracy. Importantly, children with DD were able to retain the gains in speed and accuracy, over a two‐week interval as effectively as typical readers. Thus, children with DD were as effective in the acquisition and retention of tactile discrimination of braille letters as typical readers of the same age. The results do not support the notion of a general procedural learning disability in DD.     

Procedural learning and automatization process in children with developmental coordination disorder and/or developmental dyslexia

ObjectiveThere is increasing evidence to suggest that developmental dyslexia (DD) and developmental coordination disorder (DCD) actually form part of a broader disorder. Their frequent association could be justified by a deficit of the procedural memory system, that subtends many of the cognitive, motor and linguistic abilities that are impaired in both DD and DCD. However, studies of procedural learning in these two disorders have yielded divergent results, and in any case no studies have so far addressed the issue of automatization (dual-task paradigm).MethodsWe administered a finger tapping task to participants aged 8–12 years (19 DCD, 18 DD, and 22 with both DD and DCD) to explore procedural learning and automatic movements in these three groups of children, comparing motor performances at the prelearning stage, after 2 weeks of training, and in a post-training dual-task condition.ResultsFirst, results indicated that all the children were able to learn a sequence of movements and even automatize their movements. Second, they revealed between-groups differences in procedural/automatization learning abilities, setting the DCD group apart from the other two. Third, contrary to our expectations concerning comorbidity, they suggested that the DD + DCD association does not have an additional impact on behavioral performances.     

DIAGNOSTIC PSYCHOLOGICAL TESTING FOR READING/LEARNING DISORDERS IN PRESCHOOL CHILDREN

ABSTRACT

The assessment of preschool children who are at risk for having specific language/learning disorders when they enter school is a complex undertaking which must involve examining a wide variety of developmental processes. In addition to a thorough medical, developmental and academic history, the clinician should obtain data regarding perceptual‐motor functioning, language and cognitive development, nominal recall, cerebral dominance and directionality, sequential memory, and the integrity of basic sensory modalities. Although the diagnosis of potential learning disorders in preschool children 1s difficult because of the variability in developmental rate of young children, a systematic evaluation of the developmental functions which are classically associated with learning disabilities allows the psychologist to make a responsible and generally accurate statement of the child's current functioning and future potential     

Assessment of Reading and Learning Disabilities A Research-Based Intervention-Oriented Approach

Assessment practices for children with learning disabilities (LD) in reading are driven by the three primary components of the federal definition of LD: discrepancy, heterogeneity, and exclusion. This article reviews the implications of these three components for the assessment of children with reading disabilities and other forms of LD. We propose a rationale and procedures for more efficient approaches to the identification of children as learning disabled in reading or at-risk for these disabilities that are aligned with research on reading disabilities and other forms of LD. This approach emphasizes the assessment of academic skills and their components in an effort to develop intervention plans. Intelligence tests are not necessary for the identification of children as learning disabled and do not contribute to intervention planning.     

Learning Abilities and Disabilities: Generalist Genes, Specialist Environments

ABSTRACT— Twin studies comparing identical and fraternal twins consistently show substantial genetic influence on individual differences in learning abilities such as reading and mathematics, as well as in other cognitive abilities such as spatial ability and memory. Multivariate genetic research has shown that the same set of genes is largely responsible for genetic influence on these diverse cognitive areas. We call these "generalist genes." What differentiates these abilities is largely the environment, especially nonshared environments that make children growing up in the same family different from one another. These multivariate genetic findings of generalist genes and specialist environments have far-reaching implications for diagnosis and treatment of learning disabilities and for understanding the brain mechanisms that mediate these effects.     

Motor sequence learning and reading ability: is poor reading associated with sequencing deficits?

Although it is widely assumed that children with learning disabilities have "sequencing problems," these have not been well specified. A non-verbal serial reaction time (SRT) paradigm was used to evaluate motor sequence learning in 422 children between ages 7 and 11 in relation to reading, cognitive ability level, and attention problems. The children demonstrated the response profile typically associated with motor sequence learning, but the component of the profile indicative of implicit sequence learning was not reliably associated with any of the predictors. Cognitive ability predicted overall response time; cognitive ability, reading, and attention problems each predicted overall accuracy. Explicit learning was predicted by cognitive ability, but not by reading or attention problems. Thus, we found no evidence that poor reading is preferentially associated with a domain general deficit in sequential learning.     

两类数学学习困难小学儿童抑制控制水平的实验研究

为考察单纯型数学困难与混合型数学困难小学儿童的抑制控制水平及特点,使用Stroop色词命名测验和颜色匹配反转作业,对各30名的单纯型困难、混合型困难和对照组小学儿童的优势反应抑制能力进行测试、分析。结果发现:单纯型数学困难儿童抑制优势反应的能力显著低于对照组,但其对事物初次学习的能力与对照组相当;混合型数学困难儿童在对事物初次学习能力及对优势反应的抑制能力方面均显著低于对照组儿童,其中对事物的初次学习能力也显著低于单纯型数学困难儿童。     

A cognitive-behavioral intervention program for students with special reading disabilities

Interaction among cognitive, meta-cognitive, and emotional factors seems to play a determining part in achievement behavior and especially in scholastic performance. In this study some preliminary results are presented of the implementation of a multidimensional cognitive-behavioral psychoeducational program especially designed for students with reading disabilities in which parents and teachers also take part. The aim of the program was to provide students with appropriate emotional and cognitive skills with which to address their learning problems. First results on the efficacy of the implemented program to 20 primary school boys and girls with special reading disabilities encourage research on management of learning problems with focus on cognitive and emotional aspects in which parents and teachers contribute. Research including a control group is necessary.     

发展性计算障碍儿童的数认知

发展性计算障碍作为一种特异性学习障碍,影响儿童的数学成就与数学学习观念,因而引起了多学科研究的关注和重视。文章分析了发展性计算障碍领域在数认知方面的已有研究,揭示了发展性计算障碍的数认知缺陷及内部差异,从一般认知加工障碍与数字加工模块障碍两个角度阐述了发展性计算障碍的可能成因,最后对当前研究进行了小结与展望,认为数认知缺陷的复杂关系、亚类型特征、成因之间的相互作用与机制还需进一步研究     

Are developmental disorders like cases of adult brain damage? Implications from connectionist modelling

It is often assumed that similar domain-specific behavioural impairments found in cases of adult brain damage and developmental disorders correspond to similar underlying causes, and can serve as convergent evidence for the modular structure of the normal adult cognitive system. We argue that this correspondence is contingent on an unsupported assumption that atypical development can produce selective deficits while the rest of the system develops normally (Residual Normality), and that this assumption tends to bias data collection in the field. Based on a review of connectionist models of acquired and developmental disorders in the domains of reading and past tense, as well as on new simulations, we explore the computational viability of Residual Normality and the potential role of development in producing behavioural deficits. Simulations demonstrate that damage to a developmental model can produce very different effects depending on whether it occurs prior to or following the training process. Because developmental disorders typically involve damage prior to learning, we conclude that the developmental process is a key component of the explanation of endstate impairments in such disorders. Further simulations demonstrate that in simple connectionist learning systems, the assumption of Residual Normality is undermined by processes of compensation or alteration elsewhere in the system. We outline the precise computational conditions required for Residual Normality to hold in development, and suggest that in many cases it is an unlikely hypothesis. We conclude that in developmental disorders, inferences from behavioural deficits to underlying structure crucially depend on developmental conditions, and that the process of ontogenetic development cannot be ignored in constructing models of developmental disorders.