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Neuroanatomical evidence indicates that the lateral pallium (LP) of ray-finned fishes could be homologous to the hippocampus of mammals and birds. Recent studies have found that hippocampus of mammals and birds is critical for learning geometric properties of space. In this work, we studied the effects of lesions to the lateral pallium of goldfish on the encoding of geometric spatial information. Goldfish with telencephalic lesions were trained to search for a goal in a rectangular-shaped arena containing one different wall that served as the only distinctive environmental feature. Although fish with lateral pallium lesions learned the task even faster than sham and medial pallium (MP)-lesioned animals, subsequent probe trials showed that they were insensitive to geometric information. Sham and medial pallium-lesioned animals could use both geometric and feature information to locate the goal. By contrast, fish with lateral palium lesions relied exclusively on the feature information provided by the wall of a different colour. These results indicate that lesions to the lateral pallium of goldfish, like hippocampal lesions in mammals and birds, selectively impair the encoding of geometric spatial information of environmental space. Thus, the forebrain structures of teleost fish that are neuroanatomically equivalent to the mammalian and avian hippocampus also share a central role in supporting spatial cognition. Present results suggest that the presence of a hippocampal-dependent memory system implicated in the processing of geometric spatial information is an ancient feature of the vertebrate forebrain that has been conserved during the divergent evolution of different vertebrate groups. [ABSTRACT FROM AUTHOR]

The geometric properties of bounded space have attracted considerable attention as a source of spatial information that can guide goal navigation. Although the use of geometric information to navigate has been observed in every species studied to date, the neural mechanisms that support the representation of geometric information are still debated. With the purpose of investigating this topic, we trained pigeons with lesion to the hippocampal formation to search for food in a rectangular-shaped arena containing one wall of a different color that served as the only distinctive environmental feature. Although lesioned pigeons learned the task even faster than control animals, probe trials showed that they were insensitive to geometric information. Control animals could encode and use both geometric and feature information to locate the goal. By contrast, lesioned pigeons relied exclusively on the feature information provided by the wall of a different color. The results indicate that the avian hippocampal formation is critical for learning the geometric properties of space in homing pigeons. [ABSTRACT FROM AUTHOR]