The hippocampus, memory, and spatial function

AbstractThe hippocampal system provides a beautiful example of how different classes of neuronal network in the brain work together as a system to implement episodic memory, the memory for particular recent events. The hippocampus contains spatial view neurons in primates including humans, which provide a representation of locations in viewed space, built in a ventromedial visual stream that reaches the parahippocampal scene or place area. These representations can be combined with object and temporal representations to provide an episodic memory about what happened where and when. A key part of the system is the CA3 system with its recurrent collateral connections that provide a single attractor network for these associations to be learned. The computational generation of time, encoded by time cells in the hippocampus, is described, and this leads to a theory of hippocampal replay and reverse replay. The computational operation of a key part of the architecture, the recall of memories to the neocortex, which takes part in memory consolidation, is described. Reward signals from the orbitofrontal are incorporated into hippocampal episodic memory, and in addition influence cholinergic neurons, so are involved in memory consolidation.