Intraretinal transfer of a learned visual shape discrimination in goldfish after section and regeneration of the optic nerve brachia

Abstract

In goldfish the optic nerve fibers which subserve dorsal and ventral halves of the retina separate anatomically into lateral and medial optic nerve brachia before projecting to different regions of the optic tectum. In this species it is known that surgical interruption of the optic nerve produces only temporary blindness since the optic nerve fibers are able to regenerate and in time re-establish proper connections within the tectum. By cutting one or the other of the brachia, vision was temporarily restricted to one half of the visual field. The fish were then trained to discriminate between a vertical and a horizontal rectangle using one half of the visual field of one eye. The fish were blinded in the other eye and in addition training was always discontinued long before vision was restored to the initially operated brachium. Finally, the initially unoperated brachium was cut. In subsequent behavioral tests all subjects displayed positive intraretinal transfer of the learned discrimination across the horizontal meridian.