Topological relation of chick thalamofugal visual projections with hyper pallium revealed by three color tracers

In birds, there are two visual projections from retina to higher pallium, i.e., tectofugal and thalamofugal pathways. The latter one is lateralized in chick and suggested to be involved in visually evoked social behavior, like recognition of novelty, predator, and conspecific animals. We wanted to establish functionally relevant topological connection map between thalamic nuclei and hyperpallium apicale (HA) and carried out tracing study with three color fluorescent tracers. The tracers were serially injected in HA either along with the medial-lateral (M-L) or anterior-posterior (A-P) axis. We found that M-L axis and A-P axis in HA were transferred into the dorsal-ventral axis and the medial-lateral axis, respectively within the nucleus geniculatus lateralis pars dorsalis (GLd). In another word, the medial part of nucleus dorsolateralis anterior thalami pars lateralis (DLLv) projected to anterior part of HA and the ventral part of nucleus dorsolateralis anterior thalami pars lateralis pas ventralis (DLLd) projects to lateral HA. This result suggests that thalamus would process information in parallel through each subnuclei and elaborate coordination among them in relation to topological map presented in higher pallium.