Invited Paper

The Cortico-hippocampal Circuit: The Brain’s Center for Mapping and Declarative Memory


  • Güneş Ünal

Received Date: 11.09.2018 Accepted Date: 27.02.2019 J Ankara Univ Fac Med 2019;72(1):13-23

Perceived stimuli from the external world are relayed to various association cortices after they reach their respective primary cortices. Information to be encoded as long-term memory is relayed to the dentate gyrus via perirhinal/parahippocampal and entorhinal cortices. This cortico-hippocampal circuit connecting the association cortices to the hippocampus via 3-4 synapses, forms the neuronal basis of declarative memory. Hippocampus, the most distant structure of this neuronal system from the external world, carries out the acquisition and consolidation of long-term memories. In fact, hippocampus is a mapping station that associates various cortical information to produce meaningful wholes. Putting together the semantic information to be encoded as long-term memory, hippocampus works as a mnemonic navigation system. The neuronal mechanism underlying this wide-ranging mapping capacity has evolved for spatial navigation. Principal glutamatergic cells of the CA3 and CA1 regions of hippocampus have been identified to be place cells. Similar location-encoding cells have been found in the entorhinal cortex, which provides the bulk of input to the hippocampus. Accordingly, it is theorized that inputs relayed to the central parts of the brain from the external world through different sensory systems, start forming meaningful gestalts once at the entorhinal cortex. In contrary, the perirhinal/parahippocampal cortex, providing the densest input to the entorhinal region, has not been sufficiently investigated. An important reason is that in these regions, no neuronal types showing a direct relationship with the external world, such as location-encoding cells, have been discovered. However, it is understood that the perirhinal cortex, remaining very silent in in vivo recordings, is a critical filtering station determining the inputs to be relayed to the hippocampus. This review focuses on the neuroanatomical correlates, monosynaptic connections, unique electrophysiological properties and differential roles in memory processes of the structures that make up the cortico-hippocampal circuit-brain’s center for mapping and declarative memory.

Keywords: Hippocampus, Parahippocampal, Rhinal, Navigation, Declarative Memory

Full Text (Turkish)