Functional Anatomy in Relation to Myelin Maturation

Abstract

Neural organization of cerebral activity in adult and child can be investigated by means of MRI with fMRI and DTI: MRI with fMRI analyses cortical haemodynamic responses correlated to neuronal activity, whereas DTI describes the spatial orientations of the white matter fibres. The fMRI patterns of cortical activity in children more than eight years old overlap the anatomical localization in adults except for the frontal and posterior parietal cortical areas, where BOLD responses in children are often difficult to arouse. This confirms what is currently known: myelin maturation is complete in these areas only in young adulthood. In neonates and young children, depending on the higher cortical cell concentration than adults and the increase in synaptic density up to the age of four-eight years, signal changes detected by BOLD may vary drastically. BOLD signal amplitude may be lower than that found in adults due to the reduced dynamic range during haemodynamic responses, or negative due to the local increase in HbR not fully compensated by the rise in CBF. The administration of sedatives or anaesthesia in children to perform MR scans can influence the BOLD signal: signal amplitude could decrease dramatically and the activated areas could be smaller in extension, indicating a fundamental role of the level of consciousness. BOLD signal analysis can supply useful data on the maturation processes of myelin and the cerebral cortex.