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International audience; Background:Patients with autism have been often reported to have a smaller corpus callosum (CC) than control subjects.; Methods:We conducted a meta-analysis of the literature, analyzed the CC in 694 subjects of the Autism Brain Imaging Data Exchange project, and performed computer simulations to study the effect of different analysis strategies.; Results:Our meta-analysis suggested a group difference in CC size; however, the studies were heavily underpowered (20% power to detect Cohen's d = .3). In contrast, we did not observe significant differences in the Autism Brain Imaging Data Exchange cohort, despite having achieved 99% power. However, we observed that CC scaled nonlinearly with brain volume (BV): large brains had a proportionally smaller CC. Our simulations showed that because of this nonlinearity, CC normalization could not control for eventual BV differences, but using BV as a covariate in a linear model would. We also observed a weaker correlation of IQ and BV in cases compared with control subjects. Our simulations showed that matching populations by IQ could then induce artifactual BV differences.; Conclusions:The lack of statistical power in the previous literature prevents us from establishing the reality of the claims of a smaller CC in autism, and our own analyses did not find any. However, the nonlinear relationship between CC and BV and the different correlation between BV and IQ in cases and control subjects may induce artifactual differences. Overall, our results highlight the necessity for open data sharing to provide a more solid ground for the discovery of neuroimaging biomarkers within the context of the wide human neuroanatomical diversity.

Les troubles du spectre de l’autisme (TSAs) sont caracterises par une alteration de la communication sociale, des interets restreints et stereotypes ou comportements stereotypes (DSM-5 [1] ). Touchant environ 1 % de la population, ils sont un defi societal majeur en termes de precocite de diagnostic et de developpement de strategies therapeutiques. Des avancees scientifiques mettent aujourd’hui en evidence dans les TSAs des alterations de cognition sociale et non sociale, avec des correlats neuro-anatomiques. Ceux-ci sont etudies par des techniques d’imagerie structurales (IRM), necessitant d’etre completes par des donnees fonctionnelle (ex. IRMf, EEG). L’EEG est la technique de neuro-imagerie la plus couramment utilisee en routine clinique du fait de sa faisabilite a tout âge et de son faible cout. Elle a montre un role important dans l’etude de l’electrophysiologie chez l’homme. Le rythme alpha 8–12 Hz (RA) est decrit particulierement durant l’etat de repos chez les individus. Elle a ete associee a l’inhibition sensorielle et cognitive [2] . Beaucoup d’etudes ont montre chez les sujets avec TSA une activite du rythme alpha anormale [3] , [4] ainsi qu’une faible suppression en reponse a l’observation d’action [5] . Cependant, les etudes n’identifient pas de pattern du RA consistant chez les sujets TSAs. Notre etude vise a tester la reproductibilite de ces resultats avec des sujets TSA diagnostiques dans le service de pedopsychiatrie et des sujets controles a l’etat de repos et ayant chacun beneficie d’un EEG clinique dans le service d’explorations fonctionnelles au sein de l’hopital Robert-Debre. Ces donnees ont permis l’analyse du RA de 49 sujets TSA apparies en âge et sexe avec des controles, soit 3 fois plus que dans la litterature scientifique, sans difference statistiquement significative. Cette absence de resultats questionne la litterature anterieure en matiere d’heterogeneite phenotypique et methodologique.

We investigate the behavior of fluid–particle mixtures subject to shear stress, by mean of direct simulation. This approach is meant to give some hints to explain the influence of interacting red cells on the global behavior of the blood. We concentrate on the apparent viscosity, which we define as a macroscopic quantity which characterizes the resistance of a mixture against externally imposed shear motion. Our main purpose is to explain the non-monotonous variations of this apparent viscosity when a mixture of fluid and interacting particles is submitted to shear stress during a certain time interval. Our analysis of these variations is based on preliminary theoretical remarks, and some computations for some well-chosen static configurations. To cite this article: A. Lefebvre, B. Maury, C. R. Mecanique 333 (2005).