Fimbria-fornix transections disrupt the ontogeny of delayed alternation but not position discrimination in the rat.

In Experiment 1, Long-Evans rat pups received fimbria-fornix transections or sham surgery on Postnatal Day 10 (PND10) and were then trained on PND23 to perform either a discrete-trials delayed alternation (DA) or a simple position discrimination (PD) task in a T maze. Rat pups in both surgical conditions learned the PD task within five 12-trial blocks of training. However, only sham-operated pups learned the DA task. In Experiment 2, performance of DA emerged between PND19 and PND27 in sham-operated pups but failed entirely to develop in pups with early lesions. In Experiment 3, fornix-transected pups that were given extended DA training (132 trials) on PND23-PND24 showed some improvement in performance but remained impaired in relation to sham-operated controls. These findings implicate the limbic system in the postnatal development of DA but not PD and suggest that dual-process theories of memory may be relevant to the psychobiology of cognitive development.