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.