Figure 1.
Song system schematic and tyrosine hydroxylase staining in NIf. A, Schematic diagram of the three major song system pathways: premotor, anterior forebrain, and ascending auditory. HVC, which is part of all three pathways, receives auditory input indirectly from Field L via NIf. Field L is the primary forebrain structure that receives auditory input from the thalamic nucleus Ovoidalis. NIf provides the major auditory input to HVC. The anterior forebrain pathway includes HVC, Area X, DLM, LMAN, and RA. The premotor pathway includes HVC and RA. Area X, Song-related region of the basal ganglia; DLM, medial portion of the dorsolateral nucleus of the anterior thalamus; Field L, primary thalamorecipient auditory area of the telencephalon; LMAN, lateral portion of the magnocellular nucleus of the anterior nidopallium; Ov, nucleus Ovoidalis of the thalamus; Resp., respiratory areas of the brainstem; Syrinx, avian vocal organ. B, Parasaggital brain section labeled with an antibody to tyrosine hydroxylase (TH). NIf is densely innervated with TH-positive fibers. Arrowheads indicate borders of NIf.