Functional differentiation in the transverse plane of the hippocampus: An update on activity segregation within the DG and CA3 subfields

•Functionally dissociable dorsal hippocampus transverse subnetworks generate asymmetrical activity patterns in distinct subfields.•Functionally dissociable dorsal hippocampus transverse subnetworks generate asymmetrical activity patterns in distinct subfields.•Some functional modalities retain transverse segregation as information is propagated through the transverse axis of the trisynaptic circuit (DG, CA1), whilst others are integrated (CA3).•These features could provide a basis for the pattern separation and completion functions of distinct hippocampal subfields. Decades of neuroscience research in rodents have established an essential role of the hippocampus in the processing of episodic memories. Based on accumulating evidence of functional segregation in the hippocampus along the longitudinal axis, this role has been primarily ascribed to the dorsal hippocampus. More recent findings, however, demonstrate that functional segregation also occurs along transverse axis of the hippocampus, within the hippocampal subfields CA1, CA2, CA3, and the dentate gyrus (DG). Because the functional heterogeneity within CA1 has been addressed in several recent articles, here we discuss behavioral findings and putative mechanisms supporting generation of asymmetrical activity patterns along the transverse axis of DG and CA3. While transverse subnetworks appear to discretely contribute to the processing of spatial, non-spatial, temporal, and social components of episodic memories, integration of these components also occurs, especially in the CA3 subfield and possibly downstream, in the cortical targets of the hippocampus.