Spatial and visual discrimination learning in CD1 mice: Partial analogy between the effect of lesions to the hippocampus and the amygdala

CD1 mice with dorsal hippocampal and central amygdaloid lesions were submitted to three radial eight-arm maze tasks requiring various degrees of spatial and nonspatial information processing. The results show that, on the standard version of the radial maze, only hippocampal lesions disrupted performance. In the spatial four-baited path task, both hippocampal and amygdaloid lesions increased the errors and modified the patterns of arm choice. Finally, on the visually cued four-baited path task, the two lesions did not affect any quantitative aspect of performance but a strong and unexpected effect of amygdaloid lesions on the patterns of arm choice was found. Taken together, the results indicate i) an effect of hippocampal lesions in all situations that require performing a spatial discrimination, and ii) an effect of amygdaloid lesions in all situations that require distinguishing between baited and unbaited arms, whatever the modality-spatial or visual-being relevant for discriminating the two sets of arms. The analogy between the effects of hippocampal and amygdaloid lesions specifically observed in the spatial four-baited path task suggests that these two limbic areas can exert a similar control on performance in tasks involving mapping operations based upon the discrimination of rewarded and nonrewarded reinforced locations.