Progress in the neurobiology of learning and memory has benefitted recently by the discovery that the hippocampus and associated brain structures play an important role in "working memory," the type of memory that allows us to recall specific recent events. Major successes in creating animal models of working memory have come from the development of the delayed non- match to sample (DNMS) paradigm, a working memory test that involves three sequential phases: A cue phase when the memory cue is presented, a delay phase during which the animal must remember the cue, and a choice phase during which the animal must recognize and reject the memory cue in favor of an alternative. Investigators have shown that damage to the hippocampal system results in severe impairments on performance in DNMS, indicating that this system is critical to information processing for working memory. This research is aimed at determining what role the circuitry of the hippocampus plays in DNMS. Dr. Eichenbaum's strategy is to exploit the rats' striking learning and memory capacities with olfactory and spatial stimuli to describe the neural correlates of memory for these distinct types of information. He is recording the electrophysiological activity of single neurons in the hippocampus as rats perform DNMS tasks using either odors or places as the memory cues. By comparing the firing rates of neurons across the three phases of the task, he will be able to identify which component of memory activates hippocampal circuits, that is, whether the hippocampus is primarily involved in storage (cue phase), in holding (delay phase), or in recognition (choice phase). In addition, by comparing neuronal firing rates across the two categories of memory cues (odor and place), he will be able to determine the general, rather than stimulus-specific, qualities of cues that are processed by the hippocampus.
