DescriptionThere are inconsistencies regarding the role of the hippocampus in many forms of spatial and nonspatial learning, including Pavlovian trace fear conditioning (McEchron et al., 1998, Quinn et al., 2002, Rogers et al.,2006; Otto & Yoon, 2007). Emerging evidence suggests the hippocampus can be functionally dissociated along its septotemporal axis into dorsal and ventral hippocampus, which may explain some of these inconsistencies (Moser & Moser, 1998; Pitkanen et al., 2000). Excitotoxic lesions of ventral, but not dorsal, hippocampus impair the acquisition of trace fear conditioning, while lesions of either dorsal or ventral hippocampus made after conditioning impair the expression of trace fear conditioning (Yoon & Otto, 2007). The present study examined the contributions of dorsal and ventral hippocampus to a delayed reinforced alternation task and trace fear conditioning by using inactivation with the GABAA agonist, muscimol. The findings demonstrate that there is a double dissociation of dorsal and ventral hippocampus: inactivation of dorsal, but not ventral, hippocampus, dramatically impaired performance in the delayed reinforced alternation task, while inactivation of ventral, but not dorsal hippocampus attenuated the acquisition and expression of trace fear conditioning.