The two most-influential theories for hippocampal function are related to space and memory. The spatial hypothesis was supported by the seminal discovery in 1971 of cells in the hippocampus that fired bursts of action potentials when a rat traversed specific locations in space, or “place fields.” That suggested that the hippocampus was a sort of device used by the brain for mapping layouts of the environment. Data supporting that idea came from later virtual navigation studies in humans, which suggested a strong association between the hippocampus and spatial navigation. The memory hypothesis originated in 1957 and was supported by studies and observations in which hippocampal removal resulted in a loss of the ability to form new memories, particularly fact- and event-related (declarative) memories.