Effects of aspiration lesions of hippocampus or overlying neocortex on concurrent and configural object discriminations in rats

Rats with aspiration lesions of the hippocampus plus overlying neocortex or control lesions of this cortex alone were trained on five-pair concurrent object discriminations in an enclosed Y-maze and subsequently on an open maze. Acquisition of the former task was impaired only in rats with cortical lesions, but on the latter both groups were equally impaired. Recombining positive and negative stimuli into novel pairs did not disrupt performance. Acquisition of single-pair discriminations was normal or slightly impaired in lesion groups. The cortical, but not the hippocampal group, was impaired on the concurrent learning of a positive and a negative pattern configural task. Recombining stimuli did not impair performance of this task either. The study demonstrates that extensive damage to the hippocampal formation need not necessarily impair concurrent learning, and impairments seen in other studies may relate to details of experimental procedure.