The global record of memory in hippocampal neuronal activity

In humans the hippocampal region of the brain is crucial for declarative(1) or episodic(2) memory for a broad range of materials. In contrast, there has been controversy over whether the hippocampus mediates a similarly general memory function in other species, or whether it is dedicated to spatial memory processing(3-6). Evidence for the spatial view is derived principally from the observations of 'place cells'-hippocampal neurons that fire whenever the animal is in a particular location in its environment(7,8), or when it perceives a specific stimulus or per forms a specific behaviour in a particular place(3,4). We trained rats to perform the same recognition memory task in several distinct locations in a rich spatial environment and found that the activity of many hippocampal neurons was related consistently to perceptual, behavioural or cognitive events, regardless of the location where these events occurred. These results indicate that nonspatial events are fundamental elements of hippocampal representation, and support the view that, across species, the hippocampus has a broad role in information processing associated with memory.