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Abstract: Recent studies have found that hippocampus of mammals and birds and the lateral pallium of the fish telencephalon are critical for learning the geometric properties of space. Nevertheless, other studies suggest that navigation based on geometric information is primarily supported by proximal cues near the target location. According to this hypothesis, animals could use a taxon strategy to navigate an environment where only geometric cues are available and the results from lesion studies could be masking other effects related to the use of featural information. In the present study, we examined the effects of lesions to the lateral pallium of goldfish in the encoding of geometric spatial information. Goldfish with telencephalic lesions were trained to search for a goal in a rectangular-shaped arena with either one or two possible goals. Lateral pallium lesions do not interfere with goal location when the geometric information defined the goal unambiguously. Present results suggest that the geometric information is sensitive to be encoded in taxon strategies and therefore it could not depend directly on the correct functioning of the hippocampal system. [Copyright &y& Elsevier]

Abstract: There is some experimental evidence that the pallial areas of a fish''s brain are involved in distincted learning functions. Recently published data suggest that the medial pallium is essential for avoidance learning and the lateral pallium is crucial for spatial learning and is also involved in temporal aspects of the learning processes. This data joined to the proposal of homologies between medial and lateral fish pallia and pallial amygdala and hippocampus respectively, suggest that the pallial areas could have preserved their functions throughout vertebrates’ evolution. However, the functional implication of dorsal pallium that has been proposed as homologous to mammalian isocortex and transition cortex is largely unknown. In this study we analyze the role of dorsal pallium in trace and non-trace avoidance learning. Our results show the implication of this area in trace conditioning, but not in non-trace conditioning. This result allows discussion of homology proposals among lateral, dorsal, and medial pallia and hippocampus, isocortex, and pallial amygdala respectively. [Copyright &y& Elsevier]

Abstract: The subiculum is the main structure linking the hippocampus with several cortical and subcortical areas. In particular, ventral subiculum might act as an interface between the hippocampus, a contextual information processor, and cortical and subcortical processing systems related to motivation, such as the ventral striatum. Electrophysiological studies have shown a relationship between ventral subiculum and ventral striatum, namely a strong influence on mesolimbic system and the activity of dopaminergic neurons in the ventral tegmental area. Dopamine activity in this system has received special attention for its role in the latent inhibition phenomenon. However, the functional relationship between mesolimbic system and this behavioral process remains unclear. Two experiments were performed to analyze the role of ventral subiculum on latent inhibition. The results showed that ventral subiculum is involved in contextual processing that modulates the expression of latent inhibition. These findings are consistent with electrophysiological studies revealing the ventral subiculum as a structure modulating the mesolimbic DA system and DA release in the nucleus accumbens. [ABSTRACT FROM AUTHOR]