Brightness and pattern discrimination deficits in the pigeon after lesions of nucleus rotundus

Summary

Pigeons were trained to peck one of two discs on which were projected visual stimuli. One brightness and three pattern discrimination problems were presented. Correct responses were rewarded with grain. After the discriminations were learned, bilateral electrolytic lesions were placed stereotaxically in 13 birds, and sham operations were performed in three birds. Those birds with lesions in nucleus rotundus demonstrated severe deficits in performance of the visual discriminations. Following prolonged post-operative retraining, a gradual return to pre-operative levels of performance was observed. The post-operative relearning proceeded at a much slower rate than the pre-operative learning. Control birds with lesions in dorsal thalamus, telencephalon and mesencephalon, or sham operations, all showed considerable post-operative savings. On the basis of the anatomical, electrophysiological and behavioral data available at present, nucleus rotundus appears to be a thalamic relay of visual information from optic tectum to telencephalon in the bird.