Strong evidence suggests that the ventral region of the lateral telencephalic pallium
of teleost fish, a structure involved in allocentric spatial cognition, is homologous
to the hippocampus of tetrapods. This homology was first proposed on basis of anatomical
data, and subsequently confirmed by developmental, functional and behavioural studies.
Nonetheless, Saito and Watanabe [30,32] claim that not the lateral but, rather, the
medial pallium participates in goldfish spatial navigation and should be considered
the homologue of the hippocampus. Here, we further investigate the effects of selective
pallial lesions on the spatial cognition abilities of goldfish, trained in a "hole-board"
analogue task, to find the baited feeder within a 5 x 5 feeder matrix surrounded by
visual cues. The task in the present experiment is similar to that used by Saito and
Watanabe, but including thorough probe tests that enabled to define clearly the spatial
strategies employed by the animals, and, therefore, the spatial deficits caused by
the pallial lesions. The results showed that the lateral, but not the medial pallium
lesions, produced a dramatic impairment in the implementation of allocentric spatial
strategies. Thus, only lateral pallium lesioned goldfish, like hippocampus lesioned
tetrapods, failed to reach the goal when the cues in its proximity were excluded,
indicating that they used a guidance strategy. These results do not replicate Saito
and Watanabe's, but are consistent to previous data indicating a close functional
similarity between the lateral pallium of teleost fish and the hippocampus of amniotes.
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