Spatial discrimination in goldfish following bilateral tectal ablation

Goldfish were classically conditioned to discriminate between right and left or nasal and temporal presentations of a spot-of-light conditioned stimulus (CS). After the conditioning, the fish were administered bilateral optic tectum ablation followed by weekly sessions of conditioning trials to test for retention or relearning of the discrimination response. As their behavioral photosensitivity is greatly decreased, the ablates were dark-adapted prior to each session and trials were administered in darkness. Right x left discrimination was retained postoperatively but the nasal x temporal discrimination was blocked. Sham-operated controls discriminated between the nasal and temporal CS when dark-adapted and tested in darkness. Subsequent transection of the optic nerves obliterated response to the CS, indicating that tectum ablates detect and respond to the CS retinally and not extraretinally. We conclude that memory of visual spatial learning is mediated by non-tectal brain structures and that the ablate can discriminate between right- and left-eye input but sees the CS too diffusely to distinguish its location within the monocular field.