Both aging and Alzheimer's disease target the hippocampal formation and can result in mild to devastating memory impairment depending on the severity of the condition. Understanding the normal mnemonic functions of the hippocampus and related structures of the medial temporal lobe is the first step toward the development of diagnostics and treatments designed to ameliorate these potentially devastating age-related memory deficits. Here I describe findings from behavioral neurophysiological studies in which we have investigated the patterns of dynamic neural activity seen in the macaque monkey hippocampus during the acquisition of new associative memories. We report that hippocampal neurons signal the formation of newassociations with dramatic changes in their firing rate. Because these learning-related signals can occur just before behavioral learning is expressed, this suggests that these signals play a role in driving the learning process. Implications of these findings for understanding the memory deficits associated with aging and Alzheimer's disease are discussed.