Fig. 6. The central and dorsolateral SNS projection systems illustrating three components within the midbrain (cases 93 and 43, respectively). In schematics, black arrowheadsindicate labeled cells dorsal and medial to terminals, white arrowheads indicate labeled cells among labeled terminals, andarrows point to terminals ventral to labeled cells.Boxed regions represent the approximate location of each photomicrograph from individual cases. a, Schematic of the midbrain showing the combined distribution of labeled terminals (outline) and cells (diamonds; each = 4–6 cells) after all CS tracer injections. b–d, Dark-field photomicrographs of the three central SNS projection components after an individual LY injection into the CS.b, Labeled cells, not among terminals that project to the CS. c, Labeled cells among labeled CS efferent terminals. d, Labeled CS efferent terminals in a region devoid of cells that project to CS. e, Schematic of the midbrain showing the combined distribution of labeled terminals (outline) and cells (dots; each = 4–6 cells) after all DLS tracer injections. f–h, Photomicrographs of the three SNS projection components after an LY injection into the DLS. f, Labeled cells, not among labeled terminals that project to the DLS. Dark-field images of cells (g, arrows) among labeled DLS efferent terminals. h, DLS efferent terminals in a region devoid of retrogradely labeled cells. LGn, Lateral geniculate nucleus; RN, red nucleus;SNr, substantia nigra, pars reticulata;VTA, ventral tegmental area.