Hyperstriatal-tectal projections in the pigeon (Columba livia) as demonstrated by the retrograde double-label fluorescence technique.

Hyperstriatal-tectal connections were investigated in the pigeon by mapping retrogradely labeled neurons in the hyperstriatum following the injection of different fluorescent tracers (Fast Blue, Nuclear Yellow, Evans Blue) either bilaterally or unilaterally into distinct portions of the tectum. The projections were found to arise from the hyperstriatum accessorium (HA) of the Wulst, were essentially ipsilateral and topographically organized with respect to the dorsoventral and lateromedial plane of HA. No double-labeled neurons which would indicate bilateral axon branching via collaterals were observed. Some interspecies differences in the organization of the avian hyperstriatal-tectal pathways are discussed.