Organisation of the hyperstriatal projection to the ventral lateral geniculate nucleus in the chick (Gallus gallus).

In the chick forebrain, the hyperstriatum accessorium (HA), receives an orderly ascending projection from the dorsolateral thalamus, a primary visual centre. The study examines the topography of the descending projection from HA to the ventral lateral geniculate nucleus (GLv), another retino recipient region of the diencephalon. Discrete injections of horseradish peroxidase-labelled wheat germ agglutinin were placed in the HA, and reaction product was assessed in terminals within the GLv. The rostrocaudal axis of HA undergoes a 180 degrees rotation and is represented along the caudorostral axis of GLv. A comparison with other inputs to GLv, retina and optic tectum, shows that all inputs are in visuotopic register.