5.1. Corticospinal tracts
The corticospinal tract (CST) is the primary neural pathway for voluntary motor activities, especially fine movements (Jang SH, 2014). Simultaneous with the dynamic postnatal development of the brain is a similarly significant maturation of the CST, facilitated by rapid myelination (Dubois J et al., 2009; Liu Y et al., 2010). Although the lateralization in the entire CST microstructure was absent, it was detected in the spatial parts of the segmented CST such as the CST-cerebral peduncle and CST-posterior limb of the internal capsule (Saadani-Makki F et al., 2019). Previous studies have suggested a correlation between the early organization and WM maturation of CST and the development of later functional lateralization (Dubois J et al., 2009).
Rightward asymmetry at the levels of CST-cerebral peduncle and CST-posterior limb of the internal capsule were observed in male infants but not in females. However, female infants only displayed a CST asymmetry at the level of the posterior limb of the internal capsule, supporting the existence of different organization between the sexes (alignment, direction, and fiber crossing) and stronger coherence of these fibers in the right side of CST (Saadani-Makki F et al., 2019). Leftward asymmetry in the CST-cerebral peduncle and CST-posterior limb of the internal capsule was also reported in preterm neonates scanned at term equivalent age (Liu Y, et al., 2010). The sex-related spatial microstructure differences of CST that can be detected after birth are of great interest for a better understanding of the developmental changes in the motor pathway which can later predict early possible motor dysfunctions.