A cortical-hippocampal communication undergoes rebalancing after new learning

The brain's ability to consolidate a wide range of memories while maintaining their distinctiveness across experiences remains poorly understood. Sharp-wave ripples, neural oscillations that occur predominantly within CA1 of the hippocampus during immobility and sleep, have been shown to play a critical role in the consolidation process. More recently, evidence has uncovered functional heterogeneity of pyramidal neurons within distinct sublayers of CA1 that display unique properties during ripples, potentially contributing to memory specificity. Despite this, it remains unclear exactly how ripples shift the activity of CA1 neuronal populations to accommodate the consolidation of specific memories and how sublayer differences manifest. Here, we studied interactions between the anterior cingulate cortex (ACC) and CA1 neurons during ripples and discovered a reorganization of their communication following learning. Specifically, using a generalized linear model decoder, we demonstrated the pre-existence of ACC-to-CA1 communication, which is weakened during post-training sleep following learning, suggesting that ACC activity reallocates the contribution of CA1 neurons during memory formation. Interestingly, the reorganization appeared unique for a subset of CA1 superficial (CA1sup) neurons that were task inactive, whereas communication between the ACC and CA1deep neurons remained largely stable across pre- and post-training sleep. Consistent with this sublayer-selective reorganization, we found that optogenetic stimulations of the ACC preferentially suppressed CA1sup neurons while activating a unique subset of CA1 interneurons. Overall, these findings highlight an important role of the ACC in rebalancing CA1 neuronal populations' contribution in learning and memory consolidation.