Deterioration in learning and memory of inferential tasks for evaluation of transitivity and symmetry in aged SAMP8 mice

This study examined age‐dependent deficits in the learning and memory of inferential tasks, using an established senescence‐accelerated mouse model in age‐related brain dysfunction (SAMP8) and its genetically related inbred strain (SAMR1). The mice learned two sets of nonspatial odor‐odor pairs by association learning successively (i.e., A→B, X→Y, then B→C, Y→Z). They were tested in transitive inference (i.e., A→C, X→Z) and symmetrical inference (i.e., C→B, Z→Y). In the probe test of A→C, X→Z transitive inference, 1‐month‐old SAMP8 and control SAMR1 at the same age significantly chose the alternative based on transitive inference, but 4‐ and 7‐month‐old SAMP8 performed at a random chance level, in comparison with unambiguous inference by control SAMR1 at the same ages. During the test of C→B, Z→Y symmetrical inference, SAMP8 at 1 month of age made errors as frequently as control SAMR1 at the same age, but SAMP8 at 4 and 7 months of age made more errors than SAMR1 at the same ages. At 4 and 7 months of age, SAMP8 made more errors than 1‐month‐old SAMP8. Control SAMR1 did not show such an age‐related deficient. These results indicate that SAMP8 mice have age‐related learning and memory deficits in the ability to perform inferential tasks. Age‐related hippocampal dysfunction is suggested to be the cause of these age‐related deficits in old SAMP8 mice during the performance of inferential tasks mediated by declarative memory. Hippocampus 2002;12:803–810. © 2002 Wiley‐Liss, Inc.