The Ontogenetic Development of Hemispheric Lateralization During Face Processing: A Functional Magnetic Resonance Imaging Pilot Study in 7- to 9-Year-old Children

Face processing is mediated by a distributed neural network commonly divided into a \"core system\" and an \"extended system\". The core system consists of several, typically right-lateralized brain regions in the occipito-temporal cortex, including the occipital face area (OFA), the fusiform face area (FFA) and the posterior superior temporal sulcus (pSTS). It was recently proposed that the face processing network is initially bilateral and becomes right-specialized in the course of the development of reading abilities due to the competition between language-related regions in the left occipito-temporal cortex (e.g., the visual word form area) and the FFA for common neural resources.\n\nThe goal of the present pilot study was to prepare the basis for a larger follow-up study assessing the ontogenetic development of the lateralization of the face processing network. More specifically, we aimed on the one hand to establish a functional magnetic resonance imaging (fMRI) paradigm suitable for assessing activation in the core system of face processing in young children at the single subject level, and on the other hand to calculate the necessary group size for the planned follow-up study.\n\nTwelve children aged 7-9 years, and ten adults were measured with a face localizer task that was specifically adapted for children. Our results showed that it is possible to localize the core systems brain regions in children even at the single subject level. We further found a (albeit non-significant) trend for increased right-hemispheric lateralization of all three regions in adults compared to children, with the largest effect for the FFA (estimated effect size d=0.78, indicating medium to large effects). Using these results as basis for an informed power analysis, we estimated that an adequately powered (sensitivity 0.8) follow-up study testing developmental changes of FFA lateralization would require the inclusion of 18 children and 26 adults.