Effects of the lateral septum and latent inhibition on successive discrimination learning.

Damage to the lateral nucleus of the septum in the rat resulted in atypical learning to a previously meaningless stimulus. Nonreinforced preexposure to a stimulus normally makes more difficult subsequent use of that stimulus for learning. The effect of this preexposure on learning is termed latent inhibition and was demonstrated in sham operated animals. Rats in which the lateral septum was damaged demonstrated a paradoxically smaller learning deficit in the presence of a conditioned stimulus that was previously presented without reinforcement, when compared to the performance of both septal lesioned rats no receiving nonreinforced preexposure and sham operates receiving preexposure. The interaction of nonreinforced preexposure and lateral septal lesions can be explained using a proposed sensitization hypothesis.