(2008). Moreover, the linear evolutions of FA and ADC as a function of age reported in older fetuses (after 32 GW) (Bui et al. 2006), in premature infants born between 25 GW and 34 GW with a large majority of MRI performed after 33 GW (Partridge et al. 2004), and in normal newborns (Dubois et al. 2008) referred in the present model to a period corresponding to the third phase during which diffusion parameter variations Inhibitors,research,lifescience,medical follow a linear model relative to age. From a dynamic point of view and in accordance with histological

reports, we observed that myelination (phase 3) could appear early in the CSTs, followed by the OR and by the CC, respectively (Gilles 1983). One hypothesis sustaining this particular dynamical organization may rely on the fact that the extent of WM maturation can be related to the functionality Inhibitors,research,lifescience,medical and excitability of the connected cortical areas. For example, the advanced maturation of OR during gestation in the absence of exogenous visual stimulation could be related to the stimulation of the visual cortex by the pons-geniculate-occipital

waves during the rapid eye movement sleep that appears in fetuses as early as 30 GW (Graven 2008). Indeed, the structural maturation process of OR described in DTI coincides with the functional Inhibitors,research,lifescience,medical maturation of visual pathways evaluated by GSK2118436 visually evoked response in premature infants (Volpe 2008). The first phase of our model corresponding to axonal organization (<26.3 GW) coincides with the appearance of the first visually evoked responses previously observed in premature infants (22–24 GW). The second phase corresponding Inhibitors,research,lifescience,medical to myelination gliosis (26.3–34.8 GW) coincides with evolution of visually evoked responses to the principal wave forms (32–35 GW). Finally, the

third phase corresponding to the myelination coincides with the appearance of mature visually evoked response (39 GW). Within the CC, maturation is slow and heterogeneous according to the substructures. The antero-posterior Inhibitors,research,lifescience,medical functional differences of the CC are also reflected by differences in maturation dynamics with an early maturation of splenium Ergoloid (initiating phase 2 at 25.6 GW and phase 3 at 35.3 GW) and body (initiating phase 2 at 25 GW and phase 3 at 35.4 GW), and a later maturation of the genu (initiating phase 2 at 25 GW continuing until birth). According to the present results, genu remains in the myelination gliosis phase until 38 GW, showing that the third phase of maturation, that is the myelination, may occur entirely after birth. These observations are consistent with previous data reporting that the greatest variations of diffusion parameters during the postnatal period occurred in the CC and especially in the genu (Partridge et al. 2004; Lobel et al. 2009). Low genu maturation in utero could be related to the very low cognitive stimulation of the frontal lobes of fetuses during gestation (Barkovich 2000).