Delayed maturation of hippocampal trisynaptic circuitry underlies the protracted development of episodic-like memory
The ability to form high-resolution episodic memories emerges relatively late in development, but the circuit mechanisms underlying this transition are unknown. CA1 receives entorhinal input through a direct monosynaptic pathway and an indirect trisynaptic pathway via the dentate gyrus and CA3. In mice, CA3[->]CA1 innervation matured later than MEC[->]CA1 innervation, with pronounced maturation…
The development of high-resolution episodic memories is a relatively late occurrence, but the underlying circuit mechanisms remain a mystery. In mice, research has shown that the CA3 to CA1 innervation in the hippocampal circuit matures later than the MEC to CA1 connection, with the most significant maturation taking place between P20 and P24. This maturation of the trisynaptic pathway is crucial for high-resolution memory formation and is influenced by both neuronal activity and early-life experiences.
Interestingly, the mechanism by which trisynaptic pathway maturation facilitates memory is linked to the assembly of perineuronal nets around downstream parvalbumin-expressing interneurons. This process helps to mature these interneurons and integrate them into CA1 encoding ensembles during learning. In essence, activity-dependent maturation of trisynaptic circuitry offers a comprehensive explanation for the sensitive period during which high-resolution episodic memories emerge.
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