Rats' object-in-place encoding and the effect of fornix transection

Abstract

We studied the perception of simple computer-generated scenes by normal and fornix-transected Dark Agouti rats. In Experiment 1, the rats were rewarded for approaching trial-unique variable scenes differing from a constant scene that was the same across trials (constant-negative paradigm). The groups performed equivalently when scenes differed only in their objects or only in the occupied positions; however, when two scenes shared an object- place combination, the normal rats were more likely to see them as similar than were the fornix-transected rats. In Experiment 2, the rats learned to discriminate pairs of scenes. Again, there was no lesion effect when scenes differed by a single cue, object or position, but when the two scenes comprised the same objects interchanged in position, fornix-transected rats learned relatively easily. Fornix transection reduces rats' sensitivity to object-place combinations within scenes, consistent with D. Gaffan's account of scene memory as an animal analogue of episodic memory deficits in amnesia.