PL fiber pathways. A, 3D rendering of PL fiber pathways. To better visualize the fiber bundles, the 3D rendering is presented with the contralateral cortex and ipsilateral striatum after removal of the ipsilateral cortex from back coronal (top), lateral sagittal (middle), and dorsal horizontal (bottom) views. Note that axons traveling through the striatum divide into a medial thalamic and a lateral striatal and brainstem projection. B, Schematic illustration of PL bundle subdivisions. C, Photomicrograph showing how the fascicles of PL–thalamic fibers are segregated from the PL–striatal and PL–brainstem fibers within the striatum. Top right, Coronal section for orientation. D, Photomicrograph of the PL–thalamic and PL–brainstem labeled fibers. The corticothalamic bundle exits the striatum to enter the internal capsule, whereas the cortico–brainstem bundle first crosses the globus pallidus before joining the internal capsule. Top right, Coronal section for orientation. AP, Anterior–posterior distance from bregma; BS, brainstem; Cn, contralateral fibers; Inj, injection site; Str/BS, striatum/brainstem; Th, thalamus.