Partial EC outputs by degraded cues are amplified in hippocampal CA3 circuits for retrieving stored patterns.

Hippocampus is known to be important for episodic memories. Measuring of hippocampal neural ensembles is therefore important for observing hippocampal cognitive processes such as pattern completion. Previous studies on pattern completion had a limitation because the activities of CA3 were not simultaneously observed with the activities of the entorhinal cortex that project to the CA3. In addition, in previous research and modelling, distinct concepts such as pattern completion and pattern convergence have not been considered separately. Here, I used a molecular analysis technique that enables comparison of neural ensembles that evoked two successive events and evaluated neural ensembles in the hippocampal CA3 region and entorhinal cortex. By comparing neural ensembles in hippocampus and entorhinal cortex, I could obtain evidence that suggests pattern completion occurring in the CA3 region was induced by the partial input from EC. Use of the molecular-based ensemble measurement allows measuring two or more brain regions simultaneously, which can lead to insights into the cognitive functions of neural circuits.