Working memory deficits in high-functioning adolescents with autism spectrum disorders: neurpsychological and neuroimaging correlates

Working memory is a temporary storage system under attentional control. It is believed to play a central role in online processing of complex cognitive information and may also play a role in social cognition and interpersonal interactions. Adolescents with a disorder on the autism spectrum display problems in precisely these domains. Social impairments, communication difficulties, and repetitive interests and activities are core domains of autism spectrum disorders (ASD), and executive function problems are often seen throughout the spectrum. As the main cognitive theories of ASD, including the theory of mind deficit hypotheses, weak central coherence account, and the executive dysfunction theory, still fail to explain the broad spectrum of symptoms, a new perspective on the etiology of ASD is needed. Deficits in working memory are central to many theories of psychopathology, and are generally linked to frontal-lobe dysfunction. This article will review neuropsychological and (functional) brain imaging studies on working memory in adolescents with ASD. Although still disputed, it is concluded that within the working memory system specific problems of spatial working memory are often seen in adolescents with ASD. These problems increase when information is more complex and greater demands on working memory are made. Neuroimaging studies indicate a more global working memory processing or connectivity deficiency, rather than a focused deficit in the prefrontal cortex. More research is needed to relate these working memory difficulties and neuroimaging results in ASD to the behavioral difficulties as seen in individuals with a disorder on the autism spectru

Prediction of the yarn trajectories on complex braided preforms

Braiding can be used to manufacture preforms for resin transfer moulding (RTM). With braiding, many yarns are used, non-geodesic yarn paths are possible, and the interlaced structure of braids provides typical mechanical properties such as high impact strength. Previously, several models were developed to predict the fibre angles on simple, stationary braided preforms, but not for complex, non-axisymmetric preforms. This paper presents a fast and efficient model to predict the fibre angles on complex biaxially braided preforms. The model is verified with experiments on two mandrels and the experimental and numerical results show good agreement

Fully 2 D flow modeling of resin infusion under flexible tooling using unstructured meshes and wet and dry compaction properties

This article presents a model to simulate the RIFT process for complex 2 1/2D geometries in advance. Compaction and permeability experiments were carried out for two types of preform. A significant difference between dry and wet preform compaction was observed. The model takes both into account and by doing so, the general assumption, that the RIFT process can be modeled as a quasi-static process, becomes invalid. Therefore, a fully transient model is proposed, including the preform compaction flux. Experiments were carried out to validate the model. It was found that using the wet and dry preform properties leads to a good prediction of the height distributions, flow front positions and filling times

Working memory deficits in high-functioning adolescents with autism spectrum disorders: neuropsychological and neuroimaging correlates

Contains fulltext : 116784.pdf (publisher's version ) (Open Access)Working memory is a temporary storage system under attentional control. It is believed to play a central role in online processing of complex cognitive information and may also play a role in social cognition and interpersonal interactions. Adolescents with a disorder on the autism spectrum display problems in precisely these domains. Social impairments, communication difficulties, and repetitive interests and activities are core domains of autism spectrum disorders (ASD), and executive function problems are often seen throughout the spectrum. As the main cognitive theories of ASD, including the theory of mind deficit hypotheses, weak central coherence account, and the executive dysfunction theory, still fail to explain the broad spectrum of symptoms, a new perspective on the etiology of ASD is needed. Deficits in working memory are central to many theories of psychopathology, and are generally linked to frontal-lobe dysfunction. This article will review neuropsychological and (functional) brain imaging studies on working memory in adolescents with ASD. Although still disputed, it is concluded that within the working memory system specific problems of spatial working memory are often seen in adolescents with ASD. These problems increase when information is more complex and greater demands on working memory are made. Neuroimaging studies indicate a more global working memory processing or connectivity deficiency, rather than a focused deficit in the prefrontal cortex. More research is needed to relate these working memory difficulties and neuroimaging results in ASD to the behavioral difficulties as seen in individuals with a disorder on the autism spectrum.11 p

Working memory network alterations in high-functioning adolescents with an autism spectrum disorder

Aim: People with autism spectrum disorder (ASD) typically have deficits in the working memory (WM) system. Working memory is found to be an essential chain in successfully navigating in the social world. We hypothesize that brain networks for WM have an altered network integrity in ASD compared to controls. Methods: 13 adolescents (1 female) with autistic disorder (n = 1), Asperger's disorder (n = 7), and pervasive developmental disorder not otherwise specified (n = 5), and 13 typically developing control adolescents (1 female) participated in this study. Functional MRI was performed using an n-back task and in resting state. Results: The analysis of the behavioral data revealed deficits in working memory performance in ASD, but only when tested to the limit. Adolescents with ASD showed lower binary global efficiency in the working memory network than the control group with n-back and resting state data. This correlated with diagnostic scores for total problems, reciprocity, and language. Conclusion: Adolescent with higher functioning autism have difficulty with the working memory system, which is typically compensated. Functional MRI markers of brain network organization in ASD are related to characteristics of autism as represented in diagnostic scores. Therefore, functional MRI provides neuronal correlates for memory difficulties in adolescents with ASD

Altered neurotransmitter metabolism in adolescents with high-functioning autism

Item does not contain fulltextPrevious studies have suggested that alterations in excitatory/inhibitory neurotransmitters might play a crucial role in autism spectrum disorder (ASD). Proton magnetic resonance spectroscopy (1H-MRS) can provide valuable information about abnormal brain metabolism and neurotransmitter concentrations. However, few 1H-MRS studies have been published on the imbalance of the two most abundant neurotransmitters in ASD: glutamate (Glu) and gamma-aminobutyric acid (GABA). Moreover, to our knowledge none of these published studies is performed with a study population consisting purely of high-functioning autism (HFA) adolescents. Selecting only individuals with HFA eliminates factors possibly related to intellectual impairment instead of ASD. This study aims to assess Glu and GABA neurotransmitter concentrations in HFA. Occipital concentrations of Glu and GABA plus macromolecules (GABA+) were obtained using 1H-MRS relative to creatine (Cr) in adolescents with HFA (n=15 and n=13 respectively) and a healthy control group (n=17). Multiple linear regression revealed significantly higher Glu/Cr and lower GABA+/Glu concentrations in the HFA group compared to the controls. These results imply that imbalanced neurotransmitter levels of excitation and inhibition are associated with HFA in adolescents.6 p