Figure 1 Visualization of motor fibers originating from the precentral gyrus and traveling through posterior limb of the internal capsule and pons

(A) The descending tracts differentiate into 2 different components in the pons with an anterior component corresponding to the pyramidal tract (PT) and a posterior component consisting of alternate or supplementary motor fibers (aMF). (B) Examples of regions of interest (ROIs), overlaid onto a normalized fractional anisotropy image. The cortical ROI encompassed the precentral gyrus and its underlying white matter (z = 50), which could have also included some corticospinal fibers originating from premotor cortex since there are no clear gross-anatomic markers to discriminate between primary motor cortex and premotor cortex. The ROI encompassing the posterior limb of the internal capsule was drawn at z = 8 and the pontine ROIs were drawn just below the superior cerebellar peduncle at approximately z = −24. (Coordinates are given in Talairach space.)