Abstract
In the latent cue preference (LCP) task, water‐deprived rats alternately drink a salt solution in one distinctive compartment of a conditioned cue preference (CCP) apparatus and water in the other compartment over 8 days (training trials). They are then given a choice between the two compartments with no solutions present (preference test). Previous findings showed that this training procedure results in two parallel forms of learning: conditioning to water‐paired cues (a water‐CCP) and latent learning of an association between salt and salt‐paired compartment cues (a salt‐LCP). Experiment 1 examined these two types of learning in isolation. Results showed that expression of the salt‐LCP required salt deprivation during testing, but expression of the water‐CCP did not require a deprivation state during testing. Other results showed that salt‐LCP learning itself involves two distinct components: (1) the latent association among neutral cues in the salt‐paired compartment, and (2) motivational information about salt deprivation during testing. Previous findings also demonstrated roles for the dorsal hippocampus (DH), ventral hippocampus (VH), and entorhinal cortex (EC) in salt‐LCP learning. Experiment 2 examined the involvement of these structures during acquisition or expression of salt‐LCP learning. Rats with cannulas aimed at DH, VH, or EC were given infusions of muscimol, either before exposure to the salt‐paired, but not the water‐paired, compartment during training or before the preference test. Inactivation of the DH or EC impaired both acquisition and expression of the association between salt and salt‐paired compartment cues, while inactivation of the VH disrupted the influence of motivational information about salt deprivation required to express the salt‐LCP. These results suggest unique roles for the EC‐DH circuit and VH in salt‐LCP learning, as well as a functional dissociation between the DH and VH. © 2006 Wiley‐Liss, Inc.