Memory is essential for the retention of learning. In the presence of memory deficits, new learning is impaired and performance of previously learned habits deteriorates. What is the nature of memory? Where does it reside in the brain? What biological events are associated with the formation and retrieval of memory? These questions are explored in the first chapter of this volume. The answers are not final, but we have learned a great deal about memory processes during the past few decades. Memory is influenced by most of the pathological processes that influ ence the brain such as infection,...