I read an article in the July 2007 Scientific American titled The Memory Code by a Chinese researcher named Joe Tsien. His group did some studies on mice with implanted electrodes, and recorded synapse impulses while the mice were subjected to experiences that the researchers assumed would be frightening to the mice. One of them was a simulated earthquake. They found that the patterns of firings of the neurons repeated after the experiments were over, indicating apparently that the mice were remembering or re-experiencing their frightening experiences.