Time or Place? Dissociation Between Object-in-Place and Relative Recency in Young APPswe/PS1dE9 Mice

This study tests the predictions of a novel analysis of recognition memory based on a theory of associative learning, according to which recognition comprises two independent underlying processes, one relying on the to-be-recognized item having been experienced recently (self-generated priming), and the other on it being predicted by some other stimulus (retrieval-generated priming). A single experiment examined recognition performance in the amyloid precursor protein (APP)swe/PS1dE9 (APP/PS1) mouse, a double-transgenic model of Alzheimer's disease (AD), and wild type (WT) littermates. Performance on two variants of the spontaneous object recognition (SOR) was compared in 5-month-old APPswe/PS1dE9 (APP/PS1) mice, a double-transgenic model of AD, and their WT littermates, using junk objects. In the relative recency task animals were exposed to object A, and then object B, followed by a test with both A and B. In the object-in-place task the mice were exposed to both A and B, and then tested with two copies of A, occupying the same positions as the preeexposed objects. The WT mice showed a preference for exploring the first-presented object A in the relative recency task, and the copy of A in the "wrong" position (i.e., the one placed where B had been during the preexposure phase) in the object-in-place task. The APP/PS1 mice performed like the WT mice in the relative recency task, but showed a selective impairment in the object-in-place task. We interpret these findings in terms of-Wagner's (Information processing in animals: Memory Mechanisms, 1981, Erlbaum) theory of associative learning, sometimes opponent process (SOP), as a selective deficit in retrieval-generated priming.