Topography of the hyperstriatal visual projection area in the young domestic chicken

The extent and topography of the visual projection to the avian hyperstriatal complex are unresolved, results obtained from the pigeon being contradictory. The topography of this projection was mapped in 1- to 2-week-old chickens by recording electrically evoked field potentials from the hyperstriatum. Responses to stimulation of the contralateral eye extended 3 to 4 mm along the anterior-posterior axis of the Wulst. The anterior limit of the responsive area was situated approximately 1.0 mm posterior to the anterior pole of the Wulst. The responsive area included most of the lateral extent of the Wulst, to within 0.5 to 1.0 mm of the midline and 0.5 to 1.0 mm of the vallecula. Stimulation of the contralateral eye resulted in early field potentials located in the nucleus intercalatus hyperstriati accessorii, followed by later responses in the hyperstriatum accessorium. Stimulation of the ipsilateral eye resulted in a single response in the ventral hyperstriatum accessorium. No responses were recorded from the hyperstriatum intercalatus suprema, the hyperstriatum dorsale, or the hyperstriatum ventrale. A topographic relationship was found between the superior and inferior contralateral retina and the anterior and posterior regions of the visual Wulst. The nasal-temporal axis of the contralateral eye was found to be represented within a complex dorsoventral lamination of visual inputs to the hyperstriatal laminae.