Brain development relies on several maturational processes throughout infancy. Particularly, the myelination of white matter fibers occurs over different developmental periods, and at different rates along different regions and functional networks [1Yakovlev P.I., Lecours A. The myelogenetic cycles of regional maturation of the brain Regional development of the brain in early life Oxford: Blackwell (1967).  3-70

Cliquez ici pour aller à la section Références]. It plays a major role in the acceleration of neural information traveling through the axons, increasing the functional efficiency of the brain responses. Diffusion-MRI, particularly diffusion-tensor-imaging (DTI) provides a noninvasive mean to quantify microstructural properties of (developing) brain tissue, such as myelination [2Dubois J., Dehaene-Lambertz G., Soarès C., Cointepas Y., Le Bihan D., Hertz-Pannier L. Microstructural correlates of infant functional development: example of the visual pathways J Neurosci 2008 ;  28 : 1943-1948 [cross-ref]

Cliquez ici pour aller à la section Références, 3Dubois J., Dehaene-Lambertz G., Kulikova S., Poupon C., Hüppi P.S., Hertz-Pannier L. The early development of brain white matter: a review of imaging studies in fetuses, newborns and infants Neuroscience 2014 ;  276 : 48-71 [cross-ref]

Cliquez ici pour aller à la section Références]. How these measures of structural maturation are related to the functional maturation of brain responses is still poorly investigated. We aimed to evaluate the relationships between the structural maturation of white matter bundles (DTI measures) and the maturation of the corresponding functional responses (EEG measures). Visual system's maturation is notably intense during the first postnatal months, providing a good model to assess structure-function relationships during development. A first study demonstrated that the conduction speed of early visual responses was closely related to the maturation of optic radiations, suggesting that indices of structural maturation “explains” the inter-individual variability of visual responses better than infants’ age. In a follow-up study, we tested this relationship by recording EEG responses to lateralized visual stimuli and their transfer across hemispheres, in 40 infants between 6- and 24-weeks-old. Early visual responses (P1) appeared on visual areas of the contralateral hemisphere and were followed by responses on the ipsilateral hemisphere. The latency of P1 and its inter-hemispheric transfer decreased with infants’ age. In 13 infants in whom DTI data were also acquired, we showed that the increase in the conduction speed of these responses was related to the myelination of underlying white matter pathways (optic radiations and corpus callosum splenium). These correlations between structural and functional measures of maturation could help to understand whether functional outcome in “at-risk” infants might be “predicted” from early structural MRI.