[Verse 1] Picture the hippocampus, a vault built from waves, CA1 the courier, subiculum paves the road back out — this ain't a one-way street, what enters through layer two comes home through five and six, complete. Deep EC layers, five and six, the exit gate, gathering compressed stories the cortex has to wait for, no more spiral through the trisynaptic maze, straight shot output — different pathway, different days. [Chorus] Deep layers callin' — five and six, the send, CA1 and sub hand it off, that's how the circuit bends, Hippocampus to EC deep, EC deep to cortex wide, that's the return loop, baby, ride the reverse tide. Five and six, five and six, watch the message flow, out the hippocampal gate, into the cortex, go. [Verse 2] Now the clock strikes slow-wave sleep, the theta rhythm's gone, sharp-wave ripples fire off, compressed and racing on, CA3 dumps into CA1, the fast rewind machine, the day's whole afternoon replayed in a blink unseen. Chrobak and Buzsáki watched in ninety-four, ripples in the hippocampus knockin' on the deep layer door, EC neurons catch the spike train, pass it up the line, cortex gets the postcard — memory starts to align. [Chorus] Deep layers callin' — five and six, the send, CA1 and sub hand it off, that's how the circuit bends, Hippocampus to EC deep, EC deep to cortex wide, that's the return loop, baby, ride the reverse tide. Five and six, five and six, watch the message flow, out the hippocampal gate, into the cortex, go. [Verse 3] But deep EC ain't loyal to the cortex alone, it keeps a second wire, a hidden telephone, nucleus reuniens, a thalamic little hub, ferries the signal onward to the prefrontal club. Prefrontal's fishing for the context, for the schema's frame, deep EC's the go-between that carries both their names, so when you're plannin', reasonin', pulling facts to light, that reuniens relay is what's wiring the flight. [Bridge] Now test it — how you prove deep EC's really required? Silence layer five during ripples, keep it wired with an optogenetic switch, timed to the ripple's crest, knock it out mid-replay, then run the memory test. Compare the silenced night to a night that stayed intact — if consolidation drops, deep EC's the missing act. [Chorus] Deep layers callin' — five and six, the send, CA1 and sub hand it off, that's how the circuit bends, Hippocampus to EC deep, EC deep to cortex wide, that's the return loop, baby, ride the reverse tide. Five and six, five and six, watch the message flow, out the hippocampal gate, into the cortex, go. [Outro] CA1, subiculum, deep layers, cortex, done, reuniens on the side road, prefrontal is the run, the loop returns the treasure that the hippocampus found, ripple after ripple, laying memory to ground.
← C1 — The Perforant Path (Superficial EC → Hippocampus) | C3 — The Deep-to-Superficial Intrinsic Loop →