The hippocampus and contextual memory retrieval in Pavlovian conditioning.

Several theories of hippocampal function have suggested a role for the hippocampus in contextual memory retrieval. However, these theories are based on studies using permanent pretraining lesions, which confound the role of the hippocampus in learning with its role in retrieval. We argue that an alternative methodology is required to assess the role of the hippocampus in memory retrieval processes. This alternative methodology involves temporary inactivation of the hippocampus in Pavlovian paradigms that lend themselves to an examination of retrieval. An example of this approach is considered in a Pavlovian fear-conditioning paradigm. We examined the influence of hippocampal inactivation on the context-specific expression of latent inhibition, a response decrement displayed when excitatory conditioning is preceded by non-reinforced presentations of a to-be-conditioned stimulus. Reversible inactivation of the dorsal hippocampus prior to retrieval testing eliminated the context-specific expression of latent inhibition. The nature of the hippocampal role in retrieval processes is discussed in the light of these data.