For all individuals, the caudate and putamen were identified on fresh-frozen coronal tissue blocks using anatomical landmarks and tissue was collected via cryostat, using an approach that minimizes contamination from white matter and other striatal subregions and ensures RNA preservation. Fresh-frozen, right hemisphere coronal tissue blocks containing the body of the caudate and putamen, inclusive of plates 24–30 in the rostro-caudal axis, were included for analysis. The rostral face of each block was scored using a #11 scalpel blade while mounted in the cryostat. Sections were cut at 40 µm thickness, and each striatal subregion from an individual section was placed into its respective collection tube until a total of volume of ~50 mm3 was collected from each region. This approach minimizes contamination from white matter and other striatal subregions and ensures RNA preservation. The medial-lateral border between the caudate and putamen was scored to exclude the internal capsule. The lateral border of the putamen was defined by the external capsule. The ventral border of the caudate and putamen was defined by the anterior thalamic radiation of the internal capsule or the anterior commissure.
