Interocular transfer of shape discrimination in the goldfish--a reassessment of the role of the posterior commissure.

Previous work has implicated the hypothalamic horizontal commissure in the interocular transfer of learned shape information in the goldfish. In the experiments reported here, goldfish were classically conditioned to show a differential cardiac response. Fish with transection of this commissure acquired and transferred a circle/square discrimination, whereas animals with transection of the mesencephalic posterior commissure showed acquisition but not transfer of the same task. Other fish were trained on an orientation discrimination. Although all fish acquired the task, those with transection of the horizontal commissure showed transfer failure, whereas those with transection of the posterior commissure demonstrated transfer. We therefore suggest that information relating to shape is transferred via the posterior commissure, but that information relating to rotation transfers through the horizontal commissure.