Mutant mice that express the R (AB) gene in the hippocampus, blocking the action of PKA, have a selective defect for long-term contextual memory (A). Mice that express R(AP) were conditioned to freeze to the context in the form of a box illustrated in figure. The mice first walked around for a brief period of time and became familiar with the context in which they walked. They then heard a sound and received a shock delivered through the electrified grid in the floor. As a result the animals learned to associate the context of the space with shock and to freeze when placed in the box at a future time. These mice learned well and had good short-term memory at one hour for freezing to context. However, they no longer froze to context at 24 hours after conditioning, indicating a defect in a form of long-term explicit (declarative) memory that requires the hippocampus. Wild-type mice exposed to anisomycin, an inhibitor of protein synthesis, during training show a similar defect for long-term memory when tested 24 hours after conditioning (B), indicating that the same phenotype is obtained with R (AB) mutation as with inhibition of protein synthesis.