The hippocampus and mechanisms of declarative memory

The hippocampus is critical to declarative memory in humans and spatial memory in rodents. This review attempts to bridge between these two characterizations of hippocampal dependent memory, and in doing so reveal fundamental cognitive and neural coding mechanisms that are common to both. Evidence is presented that the hippocampus and its connections are critical to the establishment of a systematic organization of memories and to flexible expression of memory outside repetition of the training experience. In addition, evidence is presented that hippocampal neurons encode a broad range of experience and that these codings may be organized as representations of episodes in memory. It is suggested that these episodic codings are linked by common elements to construct an organized representation of acquired knowledge. (C) 1999 Elsevier Science B.V. All rights reserved.