S. Fall

Dysfunction of the attentional brain network in children with Developmental Coordination Disorder: a fMRI study

Children with Developmental Coordination Disorder (DCD) present impaired motor skills, frequently associated with impaired attentional and executive functions. The objective of this study was to assess the impact of DCD on effective connectivity applied to a putative model of inhibition. fMRI was performed in 9 children with DCD and 10 control children (8-13 years old) performing a go-nogo task. As previously reported, children with DCD obtained a similar score for correct inhibitions as controls, but responses were slower and more variable than in controls. Compared to controls, Structural Equation Modeling indicated that: (1) path coefficients from both middle frontal cortex (MFC) and anterior cingulate cortex (ACC) to inferior parietal cortex (IPC) increased in children with DCD particularly in the left hemisphere; (2) path coefficients between striatum and parietal cortex decreased in children with DCD in the right hemisphere. Results suggest that DCD could be characterized by abnormal brain hemispheric specialization during development. Furthermore, connectivity in the MFC-ACC-IPC network could indicate that children with DCD are less able than healthy children to easily and/or promptly switch between go and nogo motor responses. However, children with DCD seem to compensate for this poor efficiency by more actively engaging the ACC to prevent commissions allowing maintenance of a good level of inhibition.

Alertness in young healthy subjects: An fMRI study of brain region interactivity enhanced by a warning signal

An effective connectivity study was carried out on 16 young, healthy subjects performing an alertness task. The objective of this study was to develop and to evaluate a putative network model of alertness by adapting structural equation modeling to fMRI data. This study was designed to evaluate the directed interactivity of an attentional network during intrinsic and phasic alerting tasks. On the basis of theoretical hypotheses, clinical observations, behavioral data and neuroimaging studies, it was hypothesized that neural circuits in the right hemisphere including the dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex, inferior parietal cortex and the thalamus were involved. The results of this study support the existence of a common network of activated areas with significant path coefficient differences between intrinsic and phasic alertness. Functional interactivity was significantly reinforced during the phasic alertness task and appeared to preferentially involve activity in the DLPFC region, whereas the path coefficients of the model were well-balanced during intrinsic alertness. This study highlights the predominant role of the DLPFC region in maintenance of a state of alertness and in temporal preparation during an alertness task.

A New Lumped-Parameter Model of Cerebrospinal Hydrodynamics During the Cardiac Cycle in Healthy Volunteers

Our knowledge of cerebrospinal fluid (CSF) hydrodynamics has been considerably improved with the recent introduction of phase-contrast magnetic resonance imaging (phase-contrast MRI), which can provide CSF and blood flow measurements throughout the cardiac cycle. Key temporal and amplitude parameters can be calculated at different sites to elucidate the role played by the various CSF compartments during vascular brain expansion. Most of the models reported in the literature do not take into account CSF oscillation during the cardiac cycle and its kinetic energy impact on the brain. We propose a new lumped-parameter compartmental model of CSF and blood flows in healthy subjects during the cardiac cycle. The system was divided into five submodels representing arterial blood, venous blood, ventricular CSF, cranial subarachnoid space, and spinal subarachnoid space. These submodels are connected by resistances and compliances. The model developed was used to reproduce certain functional characteristics observed in seven healthy volunteers, such as the distribution (amplitude and phase shift) of arterial, venous, and CSF flows. The results show a good agreement between measured and simulated intracranial CSF and blood flows

Differences in effective connectivity between dyslexic children and normal readers during a pseudoword reading task: an fMRI study.

PURPOSE This fMRI study investigated phonological and lexicosemantic processing in dyslexic and in chronological age- and reading level-matched children in a pseudoword reading task. MATERIALS AND METHODS The effective connectivity network was compared between the three groups using a structural model including the supramarginal cortex (BA 40; BA: Brodmann area), fusiform cortex (BA 37) and inferior frontal cortex (BA 44/45) areas of the left hemisphere. RESULTS The results revealed differences in connectivity patterns. In dyslexic patients, in contrast with chronological age- and reading level-matched groups, no causal relationship was demonstrated between BA 40 and BA 44/45. However, a significant causal relationship was demonstrated between BA 37 and BA 44/45 both in dyslexic children and in the reading level-matched group. CONCLUSIONS These findings were interpreted as evidence for a phonological deficit in developmental dyslexia.

Effects of Methylphenidate on Default-Mode Network/Task-Positive Network Synchronization in Children With ADHD

Objective: A failure of the anti-phase synchronization between default-mode (DMN) and task-positive networks (TPN) may be involved in a main manifestation of ADHD: moment-to-moment variability. The study investigated whereby methylphenidate may improve TPN/DMN synchronization in ADHD. Method: Eleven drug-naive ADHD children and 11 typically developing (TD) children performed a flanker task during functional magnetic resonance imaging. The ADHD group was scanned without and 1 month later with methylphenidate. The signal was analyzed by independent component analysis. Results: The TD group showed anti-phase DMN/TPN synchronization. The unmedicated ADHD group showed synchronous activity in the posterior DMN only, which was positively correlated with response time variability for the flanker task. Methylphenidate initiated a partial anti-phase TPN/DMN synchronization, reduced variability, and abolished the variability/DMN correlation. Conclusion: Although results should be interpreted cautiously because the sample size is small, they suggest that a failure of the TPN/DMN synchronization could be involved in the moment-to-moment variability in ADHD. Methylphenidate initiated TPN/DMN synchronization, which in turn appeared to reduce variability.

Assessment of brain interactivity in the motor cortex from the concept of functional connectivity and spectral analysis of fMRI data

Functional magnetic resonance imaging (fMRI) was used to assess the contributions of movement preparation and execution of a visuomotor task in a cerebral motor network. The functional connectivity of the voxel time series between brain regions in the frequency space was investigated by performing spectral analysis of fMRI time series. The regional interactivities between the two portions of the supplementary motor area (pre-SMA and SMA-proper) and the primary motor cortex (M1), defined as a seed region, were evaluated. The spectral parameter of coherence was used to describe a correlation structure in the frequency domain between two voxel-based time series and to infer the strength of the functional interaction within our presumed motor network of connections. The results showed meaningful differences of the functional interactions between the two portions of the SMA and the M1 area depending on the task conditions. This approach demonstrated the existence of a functional dissociation between the pre-SMA and SMA-proper subregions. We therefore conclude that spectral analysis is useful for identifying functional interactions of brain regions and might provide a powerful tool to quantify changes in connectivity profiles associated with various components of an experimental task.

Use of fMRI and Structural Equation Modeling for Studying Interconnected Brain Areas within a Hypothetical Network

Functional neuroimaging first allowed researchers to describe the functional segregation of regionally activated areas during a variety of experimental tasks. More recently, functional integration studies have described how these functionally specialized areas (i.e. areas whose activity is temporally modified) interact within a highly distributed neural network. When applied to the field of functional magnetic resonance imaging (fMRI), structural equation modeling (SEM) uses theoretical and/or empirical hypotheses to estimate the effects (path coefficients) of an experimental task within a putative network. Structural equation modeling represents a linear technique for multivariate analysis of fMRI data and has been developed to simultaneously examine ratios of multiple causality in an experimental design; the method attempts to explain a covariance structure within an anatomical (constrained) model. This method, when combined with the concept of effective connectivity, can provide information on the strength and direction of the functional interactions which take place between identified nodes of a putative network. After having provided a brief reminder of the principle of the blood oxygen level-dependent (BOLD) contrast effect, the physiological bases of brain activity and the concepts of functional integration and effective connectivity, we specify the various steps in the SEM analysis and the use of fMRI data to explore putative networks of interconnected active areas.

N - 23 Préparation attentionnelle : quelle anatomie ?

Introduction L’alerte est le processus permettant de preparer a l’imminence d’un evenement ce qui optimise les performances. Elle peut etre extrinseque, declenchee par la presence d’un signal avertisseur ou intrinseque. Objectifs Notre objectif etait d’etudier les mecanismes d’alerte en IRMf par une tâche de temps de reaction simple (TRS), et de comparer alerte intrinseque et extrinseque. Methodes Nous avons evalue 16 sujets droitiers (28 ans). Le protocole d’activation cerebrale comprenait 2 tâches de TRS utilisant des stimuli visuels elementaires, l’une sans signal avertisseur (alerte intrinseque), l’autre avec signal avertisseur (alerte extrinseque) et une tâche sensori-motrice (controle). Les analyses d’imagerie fonctionnelle utilisaient le logiciel SPM version 2 localisant les regions cerebrales activees par le processus d’alerte et ensuite, les relations existant entre ces regions de maniere qualitative. Resultats Nos resultats etaient en faveur d’un reseau commun d’activation essentiellement fronto-parietale (cortex frontal dorso-lateral (BA 10, 46, 8), lobule parietal inferieur (BA 40), gyrus cingulaire anterieur (GCA) (p Discussion L’alerte intrinseque et extrinseque partagent un reseau commun d’activation fronto-parietale a predominance droite. L’activation de l’aire temporale inferieure et du gyrus fusiforme, plus surprenante peut etre liee a la discrimination des stimuli visuels, a l’implication d’un processus mnesique ou au processus attentionnel. Alerte extrinseque et intrinseque semblent cependant differer en terme d’interactions entre ces aires impliquees. Conclusion La poursuite de l’analyse en reseau des aires impliquees devrait permettre de preciser ces resultats.

Evaluation de l’activation cerebrale chez des patients deficit cognitif leger et porteurs de leucoaraiose

Objectifs Evaluer l’effet d’une leucoaraiose cerebrale importante sur les cartographies d’activation obtenues par IRMf lors d’une tâche de fluence verbale. Materiels et methodes Une sequence d’IRMf a ete realisee chez 8 (76,4 ± 3,0 ans) et 10 patients (67,6 ± 4,2 ans) respectivement avec et sans leucoaraiose. Un paradigme en blocs d’une duree de 2 minutes 33 secondes a ete utilise. Une analyse statistique de deuxieme ordre, realisee avec le logiciel SPM99 apres correction des mouvements, normalisation dans l’espace de Talairach, lissage des images avec un filtre gaussien de 8 mm, a permis d’identifier sur la base du maximum local les regions significativement activees dans les 2 groupes. Resultats Le nombre de voxels actives dans les regions frontales (seuil arbitraire de valeur de p Conclusion Les modifications detectees par IRMf chez les patients avec leucoaraiose marquee suggerent une souffrance frontale.