Inhibitory and excitatory cFos engram neurons are preferentially reactivated by sharp wave ripples

Abstract

Sharp wave ripples (SWRs) reactivate hippocampal activity patterns during memory consolidation, but whether they recruit cFos engram cells is unclear. We tagged CA1 neurons activated during sequential exploration of two spatial contexts and later identified them in vivo by optotagging. We found that the cfos engram population is composed of place cells, non-place principal cells and inhibitory interneurons. cFos-tagged place cells were reused across context exposures while maintaining context specific maps. During post-behavior rest, cFos-tagged place cells and interneurons showed stronger SWR recruitment than untagged cells, with cFos identity being more closely associated with SWR modulation than firing rate features. cFos-tagged interneurons were speed- and theta-modulated, preferentially coupled to cFos-tagged place cells during SWRs, and preferentially recruited from parvalbumin and somatostatin expressing classes. After exposure to contexts outside the original tagging experience, enhanced interneuron recruitment was attenuated, whereas tagged place cells retained elevated SWR coupling. Thus, SWRs engage excitatory and inhibitory components of a cFos-tagged spatial ensemble, linking cellular engram identity to hippocampal network dynamics during memory consolidation.