Acquisition of conditional discriminations in hippocampal lesioned and decorticated rats: evidence for learning that is separate from both simple classical conditioning and configural learning.

This study examined whether hippocampal or neocortical lesions would impair acquisition of a discrimination task using taste aversions. Rats were injected with a drug 15 min before a flavored solution-lithium chloride pairing. On alternate days, vehicle injections preceded and followed access to the same flavored solution. Rats learned to consume significantly more of the flavored solution after vehicle injections than after drug injections. Rats with hippocampal lesions or neonatal decortication performed as well as controls. Rats with hippocampal lesions also learned a similar task in which visual and textural cues predicted whether access to a flavored solution would be followed by an injection of lithium chloride or vehicle. However, these hippocampal lesions did impair performance in the Morris water task. Occasion setting may involve a type of learning dissociated from both simple classical conditioning and configural learning.