The rhinal cortices: a wall of inhibition between the neocortex and the hippocampus

Anatomical data indicate that the parahippocampal region, comprised of the perirhinal (PRC), postrhinal (POR) and entorhinal (ERC) cortices, is an essential link between neocortex and hippocampus. Lesion studies demonstrated that memory functions previously ascribed to the hippocampus depend on the integrity of the rhinal cortices. This review will consider recent data suggesting that the ERC and PRC, far from being passive relay stations, actively gate impulse traffic between neocortex and hippocampus, because they are endowed with a powerful intrinsic inhibitory system. It is proposed that the cross-talk between PRC and ERC is not organized to unrestrictedly transfer information, but to select relevant inputs. The implication of these new evidences for the propagation of epileptiform activity will be considered.