Role of CA3 and CA1 subregions of the dorsal hippocampus on temporal processing of objects.

Previous research in the dorsal CA1 and dorsal CA3 subregions of the hippocampus has been shown to play an important role in mediating temporal order memory for spatial location information. What is not known is whether the dorsal CA3 and dorsal CA1 subregions of the hippocampus are also involved in temporal order for visual object information. Rats with dorsal CA1, dorsal CA3 or control lesions were tested in a temporal order task for visual objects using an exploratory paradigm. The results indicated that the controls and the dorsal CA3 lesioned rats preferred the first rather then the last object they had explored previously, indicating good memory for temporal order of object presentation. In contrast, rats with dorsal CA1 lesions displayed a profound deficit in remembering the order of the visual object presentations in that they preferred the last object rather than the first. All three groups of rats preferred a novel object compared to a previously explored object suggesting normal detection of visual object novelty. The results suggest that only the dorsal CA1, but not dorsal CA3, region is critical for processing temporal information for visual objects without affecting the detection of new visual objects.