CA3-CA1 network: how memory decay shapes consolidation and forgetting

The hippocampus is the core brain region for long-term memory encoding, consolidation, and forgetting, yet the dynamic mechanisms underlying memory engram consolidation and forgetting remain unclear. Based on the existing hippocampal CA3-CA1 synaptic network model, combined with sparse coding and discretized synaptic plasticity, this study introduces memory strength and lifetime to investigate the processes of hippocampal memory consolidation and forgetting. The initial memory stored in a local synaptic network forms a durable engram, while subsequent memories stored in non-overlapping CA1 pyramidal neurons induce its decay. Numerical results show that memory strength depends on the efficiency of signaling cascades in regulating AMPA receptor efficacy during encoding, is further enhanced by decay-initiated consolidation, and is modulated by information complexity, synaptic input count, and excitatory-inhibitory balance. Long-term memory forgetting is driven by the decay effect, while learning efficiency and various neurodegenerative disorders modulate the initial memory lifetime by regulating this decay effect.