Lesions of the medial pallium, but not of the lateral pallium, disrupt spaced-trial avoidance learning in goldfish (Carassius auratus).

The effects of telencephalic lesions of the medial pallium (MP) and lateral pallium (LP) of goldfish on avoidance learning were studied in a two-way, shuttle response, spaced-trial avoidance conditioning situation. Animals received one trial per day, a training regime that permits the assessment of avoidance learning in the absence of stimulus carry-over effects from prior trials. Control and LP-lesioned goldfish exhibited significantly faster avoidance learning than MP-lesioned animals. These results suggest that the MP, but not the LP, is responsible for the widely described deficits in avoidance learning after lesions of the entire telencephalon. The proposal of a functional similarity between the fish MP and the mammalian amygdala, known to be involved in fear conditioning, suggests a conservative phylogenetic role of this area in avoidance learning.