Deficits in acquisition of spatial learning after dorsomedial telencephalon lesions in goldfish

Acquisition of spatial learning is an important function of mammalian hippocampus. In order to identify the brain areas in teleost fish that are homologous to mammalian hippocampus, the present study examined the effects of lesions in the dorsal area of the caudal telencephalon of goldfish (Carassius auratus) on the acquisition of spatial learning. An open-field maze that was similar to the dry version of the Morris water maze was used. The task consisted of habituation and postoperative training to reach the position of the bait. Extramaze cues were visible in the habituation sessions in experiment 1, while they were blocked and not visible in the habituation sessions in experiment 2. Only in experiment 2, there was a significant deficit in the performance in the training sessions in the goldfish with damage to the dorsomedial area of the caudal telencephalon (DM). These data showed that blocking of the extramaze cues in the habituation sessions caused deficits in postoperative acquisition of spatial learning in the training sessions in the goldfish with DM lesions. Latent learning in the habituation sessions, however, eliminated the effects of the DM lesions on spatial learning. The present study suggests that the DM plays a critical role in acquisition of spatial learning.