A hypothalamo-septo-hippocampal circuit for REM sleep-dependent consolidation of social memory

REM sleep selectively activates lateral supramammillary nucleus (SuM) to medial septum (MS) projecting neurons, and REM-specific silencing of this pathway impairs hippocampal memory consolidation.

• Why it matters: REM sleep is a key consolidation window, but the specific circuits that coordinate hippocampal memory stabilization—especially for social memory—are not well defined.
• What they did: Using fiber photometry and optrode recordings, they measured REM-selective activity in lateral SuM-MS neurons, then optogenetically silenced the projection during REM sleep. They further silenced the MS-CA2 downstream pathway during REM to dissociate memory types.
• The result: REM silencing of lateral SuM-MS impaired consolidation of both social and contextual fear memories, while REM silencing of MS-CA2 selectively disrupted social memory while sparing contextual fear memory. This defines a lateral SuM-MS-CA2 circuit for social memory alongside a direct SuM-CA2 pathway.

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