Conclusion
Using a longitudinal whole-brain FBA analysis, we have shown that important WM and GM maturational changes take place from the 33rd week GA of preterm brain development to term-equivalent age. In particular, all major cerebral WM fibers undergo significant increases in microscopic fiber density and, specially, in macroscopic fiber bundle cross-section, with the most pronounced changes occurring in the central projection fibers. In the cortical GM, the FBA metrics changes support an important increase in dendrite growth and arborisation, resulting in a complexification of the cortical geometric structure of diverse regions. Furthermore, an early music intervention given to preterm infants during NICU stay has led to an enhanced maturation of cortical regions undergoing important maturational changes from the 33rd week GA to term-equivalent age and important for auditory, cognitive and, in particular, socio-emotional processing. The effect of music on these cortical regions seems to be related to a cortical complexification, possibly in line with increase in dendrite growth and arborisation, as well as intracortical myelination. Early interventions, such as music, aiming to enrich the sensory input given to preterm infants during this important period of activity-dependent brain plasticity, might therefore play a role in these infants later clinical development. In particular, music may activate and modulate cortical regions involved in emotional processing and thus contribute to mitigate the later socio-emotional problems observed in preterm population, assisting preterm infants to achieve its full potential.