title: Functional connectivity of the entorhinal-hippocampal space circuit.
abstract: The mammalian space circuit is known to contain several functionally specialized cell types, such as place cells in the hippocampus and grid cells, head-direction cells and border cells in the medial entorhinal cortex (MEC). The interaction between the entorhinal and hippocampal spatial representations is poorly understood, however. We have developed an optogenetic strategy to identify functionally defined cell types in the MEC that project directly to the hippocampus. By expressing channelrhodopsin-2 (ChR2) selectively in the hippocampus-projecting subset of entorhinal projection neurons, we were able to use light-evoked discharge as an instrument to determine whether specific entorhinal cell groups--such as grid cells, border cells and head-direction cells--have direct hippocampal projections. Photoinduced firing was observed at fixed minimal latencies in all functional cell categories, with grid cells as the most abundant hippocampus-projecting spatial cell type. We discuss how photoexcitation experiments can be used to distinguish the subset of hippocampus-projecting entorhinal neurons from neurons that are activated indirectly through the network. The functional breadth of entorhinal input implied by this analysis opens up the potential for rich dynamic interactions between place cells in the hippocampus and different functional cell types in the entorhinal cortex (EC).
authors.affiliation: Centre for Neural Computation and Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, , 7489 Trondheim, Norway.
authors.forename: Sheng-Jia
authors.initials: SJ
authors.lastname: Zhang
authors.forename: Jing
authors.initials: J
authors.lastname: Ye
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Couey
authors.forename: Menno
authors.initials: M
authors.lastname: Witter
authors.forename: Edvard I
authors.initials: EI
authors.lastname: Moser
authors.forename: May-Britt
authors.initials: MB
authors.lastname: Moser
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D000075402:Channelrhodopsins; D018728:Entorhinal Cortex / Q000166:cytology / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D010777:Photochemistry / Q000379:methods; D051381:Rats
chemical_list: D000075402:Channelrhodopsins
keywords: border cells; entorhinal cortex; grid cells; hippocampus; optogenetics; place cells