Afferent and efferent projections of the central caudal nidopallium in the pigeon (Columba livia).

The central caudal nidopallium (NCC) is a large subdivision of the nidopallium in the pigeon brain, but its connectional anatomy is unknown. Here, we examined the connections of NCC by using tract-tracing methods. Injections of cholera toxin B-chain (CTB) in NCC labeled many neurons within NCC. Outside NCC, many labeled neurons were found in the dorsal intermediate mesopallium and medialmost part of the medial intermediate nidopallium, with a few in the intermediate (AI) and medial (AM) arcopallium. In the thalamus, labeled neurons were located in the subrotundal nucleus, the shell region of nucleus ovoidalis, and the caudal part of the dorsolateral posterior thalamic nucleus. Injections of biotinylated dextran amine (BDA) in NCC labeled many fibers running rostrocaudally within NCC. Some of these terminated in the dorsal intermediate mesopallium, but the size of the terminal field was smaller than the region of the dorsal intermediate mesopallium that provided the projection to NCC. NCC sent numerous efferents to AI and AM but few to the thalamus. In contrast, after CTB injections in the dorsal intermediate mesopallium, a few neurons were labeled in NCC, but, after BDA injections in the dorsal intermediate mesopallium, large numbers of labeled fibers were seen to project widely throughout NCC. These findings indicate that the flow of information is predominantly from the dorsal intermediate mesopallium to NCC and from there to the arcopallium (AI and AM). The arcopallial outflow to the medial hypothalamus could imply that NCC is involved in neuroendocrine and autonomic functions and is limbic in nature.