The authors draw together the results of a series of detailed computational studies and show how they are contributing to the development of a theory of hippocampal function. A new part of the theory introduced here is a quantitative analysis of how backprojections from the hippocampus to the neocortex could lead to the recall of recent memories. The theory is then compared with other theories of hippocampal function. First, what is computed by the hippocampus is considered. The hypothesis the authors advocate, on the basis of the effects of damage to the hippocampus and neuronal activity recorded in it, is that it is involved in the formation of new memories by acting as an intermediate-term buffer store for information about episodes, particularly for spatial, but probably also for some nonspatial, information. The authors analyze how the hippocampus could perform this function, by producing a computational theory of how it operates, based on neuroanatomical and neurophysiological information about the different neuronal systems con-tained within the hippocampus. Key hypotheses are that the CA3 pyramidal cells operate as a single autoassociation network to store new episodic information as it arrives via a number of specialized preprocessing stages from many association areas of the cerebral cortex, and that the dentate

1. To analyze the selectivity and the sparseness of firing to visual stimuli of single neurons in the primate temporal cortical visual area, neuronal responses were measured to a set of 68 visual stimuli in macaques performing a visual fixation task. The popula-tion of neurons analyzed had responses that occurred primarily to faces. The stimuli included 23 faces, and 45 nonface images of real-world scenes, so that the function of this brain region could be analyzed when it was processing natural scenes. 2. The neurons were selected to meet the previously used crite-ria of face selectivity by responding more than twice as much to the optimal face as to the optimal nonface stimulus in the set. Application of information theoretic analyses to the responses of these neurons confirmed that their responses contained much more information about which of 20 face stimuli had been seen (on average 0.4 bits) than about which (of 20) nonface stimuli had

The information represented in the primate hippocampus is being analysed by making recordings in monkeys actively walking in the laboratory. In a sample of 352 cells recorded in this situation, no "place" cells have so far been found. Instead, we have found a considerable population of "spatial view" cells tuned to respond when the monkey looks at small parts of the environment. We have been able to demonstrate (1) that these hippocampal neurons respond to a view of space "out there," not to the place where the monkey is; (2) that the responses depend on where the monkey is looking, by measuring eye position; (3) that the responses in some cases (e.g., CA1 but not CA3) still occur if the view details are obscured with curtains; (4) that the cells (in, e.g., CA1) retain part of their "space" tuning even in complete darkness, for several minutes; and (5) that the spatial representation is allocentric. The spatial representation is, thus, different from that in the rat hippocampus, in which place cells respond based on where the rat is located. The representation is also different from that described in the parietal cortex, where neurons respond in egocentric coordinates. This representation of space "out there" provided by primate spatial view cells would be an appropriate part of a memory system involved in memories of particular events or episodes, for example, of where in an environment an object was seen. Spatial view cells (in conjunction with whole body motion cells in the primate hippocampus, and head direction cells in the primate presubiculum) would also be useful as part of a spatial navigation system, for which they would provide a memory component. Hippocampus 1999;9:467--480. # 1999 Wiley-Liss, Inc.

We describe here hippocampal cells that respond during whole-body motion when a monkey is moved on a remote-controlled robot-mounted platform in a cue-controlled test chamber (2 x 2 x 2 m). Some of these cells responded to linear motion, and others to axial rotation. Some of these cells responded when the same motion occurred without a view of the visual field. Such cells appeared to be driven by vestibular inputs. Other cells required a view of the visual field for their response, and these cells appeared to be driv-en by the visual motion relative to the monkey of the test chamber. Further evidence that this was the case was that some of the cells responded to rotation and linear motion of the test chamber while the monkey remained stationary. Oth-er cells responded to combinations of whole-body motion and a view of the environment.