An alternative possibility is that the observed dependencies also exist in wider and less homogeneous WM regions with higher inter-subject variability but may have remained undetected due to a decreased sensitivity of the method in regions with more widespread fiber orientations or crossing tracts.
The third level was selected at the trigeminal nerve origin from the pons and the regions of interest at the middle cerebellar peduncle, pontine crossing tract, and medial lemniscus were measured on two continuous sections).
Regions of interest were placed on the caudate, putamen, globus pallidum, anterior and posterior limbs of the internal capsule, thalamus, cerebral peduncles, superior and middle cerebellar peduncles, pontine crossing tract, medial lemniscus, and the genu, body, and splenium of the corpus callosum.
In patients with TBI, the FA was also reduced in most of the regions with abundant WM, including the posterior limb of the internal capsule, whole corpus callosum, right cerebral peduncle, middle cerebellar peduncle, pontine crossing tract, and medial lemniscus, although the differences were not significant (see Supplementary Material available online at http://dx.doi.org/10.1155/2014/340936).org/10.1155/2014/340936
In regions where the degenerated pathway crosses other tracts, such as in the rostral pons, paradoxically there is almost no change in diffusion anisotropy, but a significant change in the measured orientation of fibers.
Accordingly it can see intra-voxel diffusion heterogeneity caused by crossing neuronal tracts, which is essential for an accurate mapping of axonal trajectories.
For example, in a study reporting diffusion changes in Wallerian degeneration, Pierpaoli et al. [69] found large changes in diffusion anisotropy only in regions where fibers are arranged in isolated bundles of parallel fibers but not in regions where the degenerated pathway crosses other tracts.
This suggests that the contralesional basal ganglia network is crucial for bilateral pathological gait changes; it can influence the contralesional spinal motor system through ipsilateral connections (via MLR) and the ipsilesional motor system through contralateral connections (via the basal ganglia-thalamus-cortex loop and crossed corticospinal tract).
As an individual moves and explores the environment through bimanual and unimanual activity, the crossed corticospinal tract integrity gains strength.
In their descent through the lower portion of the medulla (immediately above the junction with the spinal cord), the vast majority (80 to 90 percent) of corticospinal tracts cross, forming the point known as the decussation of the pyramids.
