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Geometry, e.g., the shape of the environment, can be used by numerous animal species to orientate, but data concerning the mouse are lacking. We addressed the question of whether mice are capable of using geometry for navigating. To test whether aging could affect searching strategies, we compared adult (3-to 5-mo old) and aged (20-to 21-mo old) C57BL/6 male mice. We established a water maze task in which spatial information is provided by one landmark proximal to the target (featural information) and by the rectangular shape of the maze (geometric information). By means of probe trials in which we manipulated the presence of these two kinds of information, we show that adult mice can use both geometry and landmark to orientate. By contrast, aged mice do not use geometry and rely exclusively on the landmark to locate the platform. This study provides the first evidence that mice are capable of using geometric information for orientation and that this ability declines in aged animals.Place learning is one of the most common approaches to study mechanisms of memory in animals. Place learning assumes that an invisible target can be found by using allothetic navigation, namely by relying on the diverse information (visual, auditory, and olfactory cues) emerging from the milieu. Thus, specific features in the environment (featural information) can be used as landmarks to orientate. In addition to featural information, the shape of the environment (that is, geometry) can be important information used during allothetic navigation. The studies of Cheng (1986) and Margules and Gallistel (1988) were the first to demonstrate that rats can process geometry and even use it preferentially as compared with landmarks to orientate themselves in an enclosed environment. These studies have been followed by others showing that not only rats (Sakamoto and Okaichi 1996;Ramos 2000;Pearce et al. 2001;McGregor et al. 2004) but also fish (Sovrano et al. 2002(Sovrano et al. , 2003, birds (Vallortigara et al. 1990;Kelly et al. 1998;Vargas et al. 2004), and monkeys (Gouteux et al. 2001) are capable of relying on geometry to orientate.Various species have been studied for their ability to navigate by means of geometric information, but there are no data concerning the mouse, although it has become an important species in cognitive neuroscience due to the generation of transgenic lines. As pointed out by Frick et al. (2000b), "mice are not little rats," and differences have been found between the two species, notably in terms of the searching strategies used to solve the water maze task (Frick et al. 2000b;Whishaw et al. 2001). Therefore, information acquired from the rat cannot be applied to the mouse without previous experimental evidence.Similar to aged humans (Perlmutter et al. 1981;Sharps and Gollin 1987;Uttl and Graf 1993), aged mice exhibit memory deficits in spatial learning tasks (Lamberty and Gower 1993;Bach et al. 1999;Frick et al. 2000a). However, other studies showed that place learning is unaffected or only partially altered in...

Our understanding of the memory reconsolidation process is at an earlier stage than that of consolidation. For example, it is unclear if, as for memory consolidation, reconsolidation of a memory trace necessitates protein synthesis. In fact, conflicting results appear in the literature and this discrepancy may be due to differences in the experimental reactivation procedure. Here, we addressed the question of whether protein synthesis in the CA3 hippocampal region is crucial in memory consolidation and reconsolidation of allocentric knowledge after reactivation in different experimental conditions in the Morris water maze. We showed (1) that an injection of the protein synthesis inhibitor anisomycin in the CA3 region during consolidation or after a single reactivation trial disrupted performance and (2) that protein synthesis is required even after a simple contextual reactivation without any learning trial and independently of the presence of the reinforcement. This work demonstrates that a simple exposure to the spatial environment is sufficient to reactivate the memory trace, to make it labile, and that reconsolidation of this trace requires de novo protein synthesis.