At the end of the terminal microelectrode mapping session, each monkey was given a lethal dose of anesthetic (sodium pentobarbital), and when areflexive, perfused transcardially with phosphate buffered 0.9% saline (PBS, pH 7.4) followed by 2-4 % paraformaldehyde in PB, followed by 2-4% paraformaldehyde with 10% sucrose in PB. The brain and spinal cord were removed separately. Cortex was separated from subcortical structures, manually flattened, and kept flat between glass slides (see Gharbawie et al, 2011 for progressive steps in flattening squirrel monkey cortex). The cortex, brainstem, and spinal cord were stored overnight in 30% sucrose in PB for cryoprotection. The cortex was cut parallel to the surface into 40 μm sections on a freezing microtome, and the sections were stained for myelin (Gallyas, 1979 (link)) to reveal the cortical locations of the lesions tracks along electrode penetrations. The brainstem was sectioned in the coronal plane and the spinal cord in the horizontal plane, both at 40 μm. Every fourth section of the brainstem and every second section of the spinal cord was processed with immunohistochemistry to reveal CTB (Qi and Kaas, 2006 (link)). Another series of brainstem and spinal cord sections was processed for cytochrome oxidase (Wong-Riley, 1979 (link)) to reveal brainstem and spinal cord architecture (Qi and Kaas, 2006 (link)).