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Search Results: 1 - 10 of 202783 matches for " Marcel P. Zwiers "
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Do we measure gray matter activation with functional diffusion tensor imaging?
René C. W. Mandl,Hugo G. Schnack,Marcel P. Zwiers,René S. Kahn,Hilleke E. Hulshoff Pol
Frontiers in Neuroscience , 2014, DOI: 10.3389/fnins.2014.00126
Abstract:
Visual Scanning in Very Young Children with Autism and Their Unaffected Parents
Wouter B. Groen,Nanda Rommelse,Tessa de Wit,Marcel P. Zwiers,Desley van Meerendonck,Rutger Jan van der Gaag,Jan K. Buitelaar
Autism Research and Treatment , 2012, DOI: 10.1155/2012/748467
Abstract: This study of gaze patterns in very young children with autism and their parents included 23 cases (with 16 fathers and 19 mothers) and 46 controls (with 14 fathers and 28 mothers). Children (mean age years) with autism met DSM-IV and ADOS-G diagnostic criteria. The participants’ gaze patterns were recorded while they viewed four simple movies that did not feature people. In children, severity of autism is related to spending more time watching irrelevant regions in one of the four movies. The mothers of children with autism showed an atypical pattern for three movies, whereas the fathers of children with autism did not show an atypical gaze pattern. The gaze pattern of the mothers was positively correlated with that of their children. The atypical viewing pattern of autistic individuals appears not to be restricted to people and social situations but is also seen in other situations, suggesting that there is a perceptual broad autism phenotype. 1. Introduction Autism spectrum disorders (ASDs) are a group of behaviorally defined disorders with impaired social interaction as a key feature, along with impairments in verbal and nonverbal communication and stereotyped and rigid patterns of behavior. There is evidence that these behavioral characteristics are accompanied by an atypical style of perception that is unique to autism [1–3]. Unlike individuals with other brain disorders, people with autism perform better than controls on tasks that involve the perception of low-level stimuli, such as discriminating visual luminance contrasts [2] and pure tones [3], but have a poorer performance on tasks involving complex stimuli [4]. The asymmetric perceptual pattern in autism has been explained using different but converging theoretical frameworks, such as the Weak Central Coherence Theory [5] and the Enhanced Perceptual Functioning model [6]. The main theme of these theoretical frameworks is that people with autism have difficulty (or are less inclined to) processing complex dynamic stimuli but are superior in processing simple static stimuli, leading to an atypical perceptual style. This atypical perceptual style may lead to difficulties in everyday life [7] if people with autism fail to identify and pay attention to relevant aspects of their environment. Failure to notice these stimuli could lead to different experiences and subsequently to different cognitive processes and behaviors during development [8], which in turn could lead to different perceptual styles, thereby forming a vicious cycle. Klin and colleagues argue that different perceptual preferences
Functional Diffusion Tensor Imaging: Measuring Task-Related Fractional Anisotropy Changes in the Human Brain along White Matter Tracts
René C. W. Mandl, Hugo G. Schnack, Marcel P. Zwiers, Arjen van der Schaaf, René S. Kahn, Hilleke E. Hulshoff Pol
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003631
Abstract: Background Functional neural networks in the human brain can be studied from correlations between activated gray matter regions measured with fMRI. However, while providing important information on gray matter activation, no information is gathered on the co-activity along white matter tracts in neural networks. Methodology/Principal Findings We report on a functional diffusion tensor imaging (fDTI) method that measures task-related changes in fractional anisotropy (FA) along white matter tracts. We hypothesize that these fractional anisotropy changes relate to morphological changes of glial cells induced by axonal activity although the exact physiological underpinnings of the measured FA changes remain to be elucidated. As expected, these changes are very small as compared to the physiological noise and a reliable detection of the signal change would require a large number of measurements. However, a substantial increase in signal-to-noise ratio was achieved by pooling the signal over the complete fiber tract. Adopting such a tract-based statistics enabled us to measure the signal within a practically feasible time period. Activation in the sensory thalamocortical tract and optic radiation in eight healthy human subjects was found during tactile and visual stimulation, respectively. Conclusions/Significance The results of our experiments indicate that these FA changes may serve as a functional contrast mechanism for white matter. This noninvasive fDTI method may provide a new approach to study functional neural networks in the human brain.
Differences in cerebral cortical anatomy of left- and right-handers
Tulio Guadalupe,Roel M. Willems,Marcel P. Zwiers,Alejandro Arias Vasquez,Martine Hoogman,Peter Hagoort,Guillen Fernandez,Jan Buitelaar,Barbara Franke,Simon E. Fisher,Clyde Francks
Frontiers in Psychology , 2014, DOI: 10.3389/fpsyg.2014.00261
Abstract: The left and right sides of the human brain are specialized for different kinds of information processing, and much of our cognition is lateralized to an extent toward one side or the other. Handedness is a reflection of nervous system lateralization. Roughly ten percent of people are mixed- or left-handed, and they show an elevated rate of reductions or reversals of some cerebral functional asymmetries compared to right-handers. Brain anatomical correlates of left-handedness have also been suggested. However, the relationships of left-handedness to brain structure and function remain far from clear. We carried out a comprehensive analysis of cortical surface area differences between 106 left-handed subjects and 1960 right-handed subjects, measured using an automated method of regional parcellation (FreeSurfer, Destrieux atlas). This is the largest study sample that has so far been used in relation to this issue. No individual cortical region showed an association with left-handedness that survived statistical correction for multiple testing, although there was a nominally significant association with the surface area of a previously implicated region: the left precentral sulcus. Identifying brain structural correlates of handedness may prove useful for genetic studies of cerebral asymmetries, as well as providing new avenues for the study of relations between handedness, cerebral lateralization and cognition.
Brain Volumetric Correlates of Autism Spectrum Disorder Symptoms in Attention Deficit/Hyperactivity Disorder
Laurence O’Dwyer, Colby Tanner, Eelco V. van Dongen, Corina U. Greven, Janita Bralten, Marcel P. Zwiers, Barbara Franke, Jaap Oosterlaan, Dirk Heslenfeld, Pieter Hoekstra, Catharina A. Hartman, Nanda Rommelse, Jan K. Buitelaar
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0101130
Abstract: Autism spectrum disorder (ASD) symptoms frequently occur in subjects with attention deficit/hyperactivity disorder (ADHD). While there is evidence that both ADHD and ASD have differential structural correlates, no study to date has investigated these structural correlates within a framework that robustly accounts for the phenotypic overlap between the two disorders. The presence of ASD symptoms was measured by the parent-reported Children’s Social and Behavioural Questionnaire (CSBQ) in ADHD subjects (n = 180), their unaffected siblings (n = 118) and healthy controls (n = 146). ADHD symptoms were assessed by a structured interview (K-SADS-PL) and the Conners’ ADHD questionnaires. Whole brain T1-weighted MPRAGE images were acquired and the structural MRI correlates of ASD symptom scores were analysed by modelling ASD symptom scores against white matter (WM) and grey matter (GM) volumes using mixed effects models which controlled for ADHD symptom levels. ASD symptoms were significantly elevated in ADHD subjects relative to both controls and unaffected siblings. ASD scores were predicted by the interaction between WM and GM volumes. Increasing ASD score was associated with greater GM volume. Equivocal results from previous structural studies in ADHD and ASD may be due to the fact that comorbidity has not been taken into account in studies to date. The current findings stress the need to account for issues of ASD comorbidity in ADHD.
Causes and consequences of cerebral small vessel disease. The RUN DMC study: a prospective cohort study. Study rationale and protocol
Anouk GW van Norden, Karlijn F de Laat, Rob AR Gons, Inge WM van Uden, Ewoud J van Dijk, Lucas JB van Oudheusden, Rianne AJ Esselink, Bastiaan R Bloem, Baziel GM van Engelen, Machiel J Zwarts, Indira Tendolkar, Marcel G Olde-Rikkert, Maureen J van der Vlugt, Marcel P Zwiers, David G Norris, Frank-Erik de Leeuw
BMC Neurology , 2011, DOI: 10.1186/1471-2377-11-29
Abstract: The RUN DMC study is a prospective cohort study on the risk factors and cognitive and motor consequences of brain changes among 503 non-demented elderly, aged between 50-85 years, with cerebral SVD. First follow up is being prepared for July 2011. Participants alive will be included and invited to the research centre to undergo a structured questionnaire on demographics and vascular risk factors, and a cognitive, and motor, assessment, followed by a MRI protocol including conventional MRI, DTI and resting state fMRI.The follow up of the RUN DMC study has the potential to further unravel the causes and possibly better predict the consequences of changes in white matter integrity in elderly with SVD by using relatively new imaging techniques. When proven, these changes might function as a surrogate endpoint for cognitive and motor function in future therapeutic trials. Our data could furthermore provide a better understanding of the pathophysiology of cognitive and motor disturbances in elderly with SVD. The execution and completion of the follow up of our study might ultimately unravel the role of SVD on the microstructural integrity of the white matter in the transition from "normal" aging to cognitive and motor decline and impairment and eventually to incident dementia and parkinsonism.Cerebral small vessel disease (SVD) includes white matter lesions (WML) and lacunar infarcts and is a frequent finding on computer tomography (CT) and magnetic resonance imaging (MRI) scans of elderly people [1]. It is associated with vascular risk factors, such as hypertension, atherosclerosis, diabetes mellitus and atrial fibrillation [2-4]. In cerebral SVD symptoms are due to either complete (lacunar syndromes) or incomplete infarction (WML) of subcortical structures leading to accompanying complaints including the lacunar syndromes, cognitive, motor (gait) and/or mood disturbances [5]. The prevalence of WML and lacunar infarcts varies considerably across studies from 5-95% and 8-
Risk factors and prognosis of young stroke. The FUTURE study: A prospective cohort study. Study rationale and protocol
Loes CA Rutten-Jacobs, Noortje AM Maaijwee, Renate M Arntz, Mayte E Van Alebeek, Pauline Schaapsmeerders, Henny C Schoonderwaldt, Lucille DA Dorresteijn, Sebastiaan Overeem, Gea Drost, Mirian C Janssen, Waander L van Heerde, Roy PC Kessels, Marcel P Zwiers, David G Norris, Maureen J van der Vlugt, Ewoud J van Dijk, Frank-Erik de Leeuw
BMC Neurology , 2011, DOI: 10.1186/1471-2377-11-109
Abstract: The FUTURE study is a prospective cohort study on risk factors and prognosis of young ischemic and hemorrhagic stroke among 1006 patients, aged 18-50 years, included in our study database between 1-1-1980 and 1-11-2010. Follow-up visits at our research centre take place from the end of 2009 until the end of 2011. Control subjects will be recruited among the patients' spouses, relatives or social environment. Information on mortality and incident vascular events will be retrieved via structured questionnaires. In addition, participants are invited to the research centre to undergo an extensive sub study including MRI.The FUTURE study has the potential to make an important contribution to increase the knowledge on risk factors and long-term prognosis in young stroke patients. Our study differs from previous studies by having a maximal follow-up of more than 30 years, including not only TIA and ischemic stroke but also hemorrhagic stroke, the addition of healthy controls and prospectively collect data during an extensive follow-up visit. Completion of the FUTURE study may provide better information for treating physicians and patients with respect to the prognosis of young stroke.Up to 12% of all stroke occur in patients between 18-50 years ("young" stroke) [1], affecting about 5000 patients each year in the Netherlands and about 2 million young people each year worldwide. In a substantial proportion of roughly one third the etiology remains unelucidated. In terms of prognosis a "young" stroke has a dramatic influence on independency and quality of life as it occurs in the period of life that people start to form families, make decisive career moves, and have an active social life. Uncertainty about long term prognosis affects choices and planning affiliated with these life events.Whereas risk factors and prognosis in patients who develop a stroke at higher ages (usually over 70 years) are among the best studied topics in clinical medicine, this does not hold true for
Standing Ring Blowup Solutions for Cubic NLS
Ian Zwiers
Mathematics , 2010,
Abstract: We prove there exist solutions to the focusing cubic nonlinear Schr\"odinger equation in three dimensions that blowup on a circle, in the sense of L^2 concentration on a ring, bounded H^1 norm outside any surrounding toroid, and growth of the global H^1 norm with the log-log rate. Analogous behaviour occurs in any higher dimension. That is, there exists data for which the corresponding evolution by cubic NLS explodes on a set of co-dimension two. To simplify the exposition, the proof is presented in dimension three, with remarks to indicate the adaptations in higher dimension.
Vortex Collapse for the L2-Critical Nonlinear Schr?dinger Equation
Gideon Simpson,Ian Zwiers
Mathematics , 2010,
Abstract: The focusing cubic nonlinear Schr\"odinger equation in two dimensions admits vortex solitons, standing wave solutions with spatial structure, Qm(r,theta) = e^{i m theta} Rm(r). In the case of spin m = 1, we prove there exists a class of data that collapse with the vortex soliton profile at the log-log rate. This extends the work of Merle and Rapha\"el, (the case m = 0,) and suggests that the L2 mass that may be concentrated at a point during generic collapse may be unbounded. Difficulties with m >= 2 or when breaking the spin symmetry are discussed.
Adaptive finite difference methods for nonlinear elliptic and parabolic partial differential equations with free boundaries
Adam M. Oberman,Ian Zwiers
Mathematics , 2014,
Abstract: Monotone finite difference methods provide stable convergent discretizations of a class of degenerate elliptic and parabolic Partial Differential Equations (PDEs). These methods are best suited to regular rectangular grids, which leads to low accuracy near curved boundaries or singularities of solutions. In this article we combine monotone finite difference methods with an adaptive grid refinement technique to produce a PDE discretization and solver which is applied to a broad class of equations, in curved or unbounded domains which include free boundaries. The grid refinement is flexible and adaptive. The discretization is combined with a fast solution method, which incorporates asynchronous time stepping adapted to the spatial scale. The framework is validated on linear problems in curved and unbounded domains. Key applications include the obstacle problem and the one-phase Stefan free boundary problem.
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