Findings from animals concerning when interactions between perirhinal cortex, hippocampus and medial prefrontal cortex are necessary for recognition memory.

Loss of recognition memory is a prominent feature of the human classical amnesic syndrome. Recognition memory requires judgments concerning prior occurrence. Such judgments can be made in a variety of ways using different types of information such as the relative familiarity of individual objects or locations, or the location of a previously encountered object, or when an object was previously encountered. We review findings of selective ablation studies which demonstrate that the perirhinal cortex, hippocampus and medial prefrontal cortex are differently involved in recognition memory processes involving these different types of information. This review also presents data from a series of disconnection analyses, which test whether the perirhinal cortex, hippocampus and medial prefrontal cortex form components of an integrated system for these recognition memory processes. These analyses reveal that it is necessary for the perirhinal cortex, medial prefrontal cortex and the hippocampus to interact, forming an integrated network, in recognition memory involving judgment of whether an object has been previously encountered in a particular place (object-in-place recognition memory) and in judging which of two objects was encountered longer ago (temporal order memory). In contrast, such interactions are not necessary when judgments are made concerning the prior occurrence of an individual item without positional information being necessary for the judgment (object memory) or concerning the prior occurrence of some item at a particular location without object information being necessary for the judgment (location memory).