Mouse hippocampus CA1 place-cell discharge typically encodes current location but during slow gamma dominance (SGdom), when slow gamma oscillations (30-60 Hz) dominate mid-frequency gamma oscillations (60-90 Hz) in CA1 local field potentials, CA1 discharge switches to represent distant recollected locations. We now report that dentate spike type 2 (DSM) events initiated by MECII-DG inputs promote SGdom and change CA1 discharge, whereas type 1 (DSL) events initiated by LECII-DG inputs do not. Just before SGdom, LECII-originating slow gamma oscillations in dentate gyrus and CA3-originating slow gamma oscillations in CA1 become optimally phase and frequency synchronized at the DSM peak when the firing rates of DG, CA3, and CA1 principal cells increase to promote DG-CA3-CA1 cofiring optimized for the 5-10 ms DG-to-CA1 neuro-transmission that coincides with SGdom. Several properties and consequences of DSM demonstrate extrahippocampal control of SGdom, identifying a cortico-hippocampal mechanism that switches between memory-related hippocampal information processing modes.
bioRxiv Subject Collection: Neuroscience