Origines de la préférence manuelle et de la latéralisation du langage et leurs relations – MaLa3

Le langage et la prédominance de la droiterie dans la population font partie de caractéristiques qui distinguent l'espèce humaine. L'hémisphère gauche est spécialisé pour le traitement du langage et le contrôle de la main chez la plupart des droitiers, de telle sorte qu’on assume souvent que les deux sont liés. En fait aucun argument direct ne permet d’affirmer qu’ils le sont. Le but de ce projet est d’évaluer le développement de la latéralisation du langage et de la préférence manuelle chez les mêmes enfants à partir du stade fœtal et jusqu’à l’âge de deux ans, la relation entre les deux asymétries, ainsi que les facteurs génétiques et environnementaux qui en sont à l’origine.
Besides the theoretical interest of the question in terms of evolution as well as infant typical development, understanding these relations might help explain why manual and language asymmetries do not develop normally in most developmental disorders. To investigate the relations between brain language lateralization and hand preference we will investigate how these two functions co-develop during infancy. Since both handedness and cerebral asymmetries for language are expressed before birth, a systematic comparison of the development of both behavioral traits needs to start before birth. Such data are clearly lacking at present and collecting them is the first subgoal of the present project.
It is still controversial whether handedness results more from genetic or environmental factors. Environment has long been shown to influence handedness, but there is a growing consensus for a genetic participation to handedness. And the question whether brain hemispheric specialization precedes the emergence of language has long been source of debate. To investigate the relationships between handedness and language lateralization we need to evaluate what genetic factors initiate both processes and how these factors interact with possible environmental factors. This is the second subgoal of the present project.
For that purpose, we project to follow 150 infants from the beginning of the mother’s pregnancy until they reach 24 months. Hand preference and language lateralization and all factors likely to influence them will be evaluated. Hand preference will first be assessed on the ultrasound recordings of the regular check-ups during pregnancy, then by behavioral handedness tests after birth. Pre-language and language lateralization will be evaluated for perception and production. For perception, non-invasive brain imaging methods (EEG and fMRI) will be combined with behavioral methods (habituation to syllables, Head Preference Procedure). Prelanguage production will be evaluated on gestures during vocal cooing, babbling and pointing. Genetic factors likely to influence asymmetries will be investigated by evaluating family handedness and by performing a restricted genetic study through saliva collecting from the infants and the parents with screening of the regions of interest that have been shown to be related to language asymmetries by molecular geneticists. Finally, all the biological and environmental factors that may impact these functional asymmetries will be recorded (e.g. position in utero, mother’s history of pregnancy).
Finally, the main goal of this project, and its originality, is to suggest a model for the developmental origins of handedness AND language lateralization and their EARLY relationships. This will be performed through the joint analysis of genetic, biological and environmental variables in the same infants and of the outcome in terms of handedness and brain language lateralization.