Episode-specific change in hippocampal CA1 neurons: real-time temporal dynamics in multi-unit firings

Abstract Episodic memory contains “what-where-when” information of personal experience. There are innumerable episodes, but how the brain processes each episode remains unknown. We discovered episode-specific synchronized activities by multiple neurons in the hippocampal CA1, which were characterized by super burst, ripple-firing, and no-firing silent periods. Since CA1 neurons exhibited episode-specific and cell-dependent diversification of plasticity at excitatory/inhibitory synapses, super burst may be a trigger event for synaptic plasticity induction, contributing to episode encoding by ripple-firings. This study demonstrated the spatiotemporal coding of episodes by multiple-CA1 neurons and the synaptic mechanisms that underpin them. These findings revealed the existence of variety of episode-specific mechanisms of CA1 neurons; episode-specific super bursts that promote diversity at excitatory/inhibitory synapses could generate thousands of ripple-firings including past memory.