Selective inhibition in CA3: A mechanism for stable pattern completion through heterosynaptic plasticity

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Memory engrams in the hippocampus (CA3) compete during retrieval, but formation mechanisms are unclear.
• Existing models use global inhibition, failing to explain sparse coding or engram competition.
• Hippocampal inhibitory neurons show feature-selective firing and plasticity, hinting at a key role.

Purpose of the Study:

• To propose and investigate a novel mechanism for engram formation and competition in the CA3 region.
• To model the role of selective inhibition mediated by excitatory-to-inhibitory (E-to-I) synapses.
• To explore how this mechanism impacts memory retrieval dynamics and accuracy.

Main Methods:

• Developed a spiking neural network model of the hippocampal CA3 region.
• Incorporated heterosynaptic plasticity at E-to-I synapses for assembly-specific inhibition.
• Simulated memory encoding and retrieval with varying degrees of engram overlap.

Main Results:

• The model generates sparse, distributed engrams in CA3, driven by a simplified dentate gyrus (DG).
• Selective inhibition significantly enhanced recall stability and accuracy compared to global inhibition.
• Model activity patterns across DG, CA3, and CA1 mimicked experimental signatures of pattern separation and completion.

Conclusions:

• Assembly-specific inhibition via heterosynaptic plasticity offers a parsimonious mechanism for CA3 engram formation and competition.
• This mechanism provides a framework for understanding how distinct memories are formed and retrieved.
• The findings yield testable predictions for future experimental research on memory mechanisms.