Context representations, context functions, and the parahippocampal-hippocampal system.

Psychologists and neurobiologists have a long-standing interest in understanding how the context surrounding the events of our lives is represented and how it influences our behavior. The hippocampal formation emerged very early as a major contributor to how context is represented and functions. There is a large literature examining its contribution that on the surface reveals an array of conflicting outcomes and controversy. This review reveals that these conflicts can be resolved by building Nadel and Willner's dual-process theory of context representations. Two general conclusions emerge: (1) There are two neural systems that can support context representations and functions-a neocortical system composed primarily of perirhinal and postrhinal cortices and a hippocampal system that includes perirhinal, postrhinal, entorhinal cortices, and the hippocampal formation. (2) These two systems are not equivalent-some context representations and functions are uniquely supported by the hippocampal system. These conclusions are discussed in the context of canonical ideas about the special properties of the hippocampal system that enable it to make unique contributions to memory.