entorhinalhippocampal

The entorhinal-hippocampal system is the functional and anatomical network connecting the entorhinal cortex with the hippocampus in the medial temporal lobe, together with related parahippocampal structures. It plays a central role in declarative memory and spatial navigation, linking perception and experience to long-term memory.

Anatomy and connectivity: The entorhinal cortex, located in the parahippocampal region, provides major input to the hippocampus. Layer II neurons project to the dentate gyrus and CA3 via the perforant path, while Layer III neurons project to CA1 and to the subiculum. The hippocampus comprises the dentate gyrus, CA1, CA3, and the subiculum, forming an intrinsic circuit that processes and relays information. Outputs travel back to the cortex through the subiculum and entorhinal projections, helping to integrate memory representations with cortical areas.

Function and dynamics: The entorhinal-hippocampal system supports encoding of episodic memories and the formation of spatial maps. EC contains grid cells that provide metric information for navigation, while hippocampal place cells encode discrete locations. The loop participates in rapid encoding followed by consolidation during sleep, with activity patterns such as theta oscillations and sharp-wave ripples that coordinate memory replay and stabilization across networks.

Clinical and research relevance: This network is sensitive to aging and neurodegenerative disease. The entorhinal cortex often shows early structural and functional changes in conditions like Alzheimer's disease, contributing to memory impairment. The entorhinal-hippocampal system remains a major focus in studies of memory formation, spatial cognition, and related disorders.