Impairment of Figure-Ground and Shape Discrimination After Lesion of Nucleus Subpretectalis in Pigeons

Abstract

Our earlier research has shown that nucleus rotundus, a thalamic nucleus processing visual information in pigeons, together with its inhibitory complex, is differentially activated in birds performing figure-ground discrimination, color discrimination, and shape discrimination (Acerbo, McInnerney, et al., in preparation). In this study, we conducted bilateral chemical lesions of nucleus subpretectalis, a major inhibitory nucleus that regulates activity of nucleus rotundus but does not process visual information directly. We trained pigeons to simultaneously perform three visual discriminations (figureground, color, and shape) using the same displays. When birds learned to perform all three tasks at high levels of accuracy, we conducted the bilateral lesions of n. subpretectalis using ibotenic acid. After a period of recovery, the birds were retrained on the same tasks to evaluate the effect of lesion on maintenance of discriminations. Preliminary results indicate that lesion of nucleus subpretectalis has no effect on color discrimination, and impairs both shape and figure-ground discrimination. These results suggest that figure-ground segregation in avian brain may occur at the level of thalamus, rather than at the cortical level as it does in primates.