High-valued seeds are remembered better: evidence for item-based spatial memory of scatter-hoarding rodents

Episodic memory of scatter-hoarding animals involves encoding and storage of memories of cached food items, in conjunction with subsequent retrieval or recovery. Although the reward values mediate the interaction of item memory and source memory, whether nonhuman animals divide their spatial memory resources between cached items of different values has never been tested. Here, we used a unique scatter-hoarder/seed system to test our ‘cache value hypothesis’, which proposes that scatter-hoarding animals will preferentially allocate spatial memory resources towards higher-valued caches. By making Edwards's long-tailed rats, Leopoldamys edwardsi, anosmic, using Triton X-100, we showed that L. edwardsi recovered more caches containing large nuts than those containing small ones, although the two kinds of nuts were equivalently cached. Our results therefore support the hypothesis that scatter-hoarding animals allocate more spatial memory resources to caches containing high-valued items. This is one of the few studies to investigate how item memory regulates source memory (order information) in the context of food storing and recovery by animals, especially by scatter-hoarding rodents. That high-valued items were remembered better than low-valued ones in our study suggests that item memory appears to be contextually associated with order information of items in animal memory processes, which is not in agreement with a previous suggestion that order information is independent of content or item information.