Introduction: A neural systems approach to space, time, and memory in the hippocampal formation

In the span of 19 years between 1957 and 1976, three discoveries catapulted the hippocampus and medial temporal lobe to the forefront of research on the neural mechanisms of learning and memory. In 1957, Scoville and Milner (1957) reported the fascinating case study of the famous patient H.M., who lost the ability to form new declarative memories after undergoing bilateral removal of the hippocampus and adjacent cortical structures. In 1973, Bliss and Lomo (1973) discovered long-term potentiation (LTP) in the hippocampus of rabbits, providing a putative cellular mechanism for the storage of memories. And in 1976, following up on a short communication published a few years earlier (O'Keefe and Dostrovsky 1971), John O'Keefe described neurons in the hippocampus that were selectively active when a rat occupied a specific location in its environment (O'Keefe and Dostrovsky 1971; O'Keefe 1976). The discovery of these place cells and the subsequent publication of O'Keefe and Lynn Nadel's (1978) extraordinarily influential book, The Hippocampus as a Cognitive Map, generated a new field of research that has blossomed into one of the most important systems for understanding cognition at the level of neural circuitry and systems.