Development of handedness, anatomical and functional brain lateralization

The present chapter offers a report on the recent literature on the neural bases of hemispheric specialization (HS), anatomical and functional developmental timecourse of HS, and on the available knowledge of their relationships with the development of handedness. Strong anatomical asymmetries can be seen located along the end of the sylvian fissure and the superior temporal sulcus (STS) as soon as the 23rd gestational week. They correspond to a leftward sulcal depth asymmetry of the Sylvian fissure coupled with a rightward asymmetry of STS. These neonatal asymmetries targeting speech processing areas do not further change with development. Different from these anatomical asymmetries, the functional asymmetries of language areas develop during childhood. Such a development is characterized at birth by a predominant interhemispheric intrinsic connectivity between homotopic areas that will evolve toward left hemisphere intrahemispheric intrinsic connectivity between anterior and posterior language poles. The development of such a typical architecture of language networks in the left hemisphere dominant for language in more than 90% of humans translates into a continuous increase in the leftward asymmetries of activation during language production throughout childhood. With regard to the rightward cerebral lateralization for visuospatial functions, neuroimaging studies tend to indicate an increase in rightward lateralization of frontal-parietal network with age during visuospatial memory and visuospatial search tasks. In addition, the spatial-attentional behavioral asymmetries emerge early (in preschool children) and, then, can be modulated by factors linked to motor asymmetry and handedness. Finally, the study of manual lateralization in relation to language development has shown the importance of considering several characteristics of manual activities. In particular, the dissociation between manipulative activities and communicative gestures in young children may open further perspectives for future research on HS.