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…
Understanding how the brain consolidates memories while preserving their distinctiveness remains a complex puzzle. Sharp-wave ripples, rhythmic neural oscillations primarily occurring in the hippocampus during rest, are crucial in this process. Recent research has also revealed functional variations among pyramidal neurons in specific layers of the hippocampus, which may contribute to the uniqueness of individual memories.
However, the exact mechanisms by which these ripple cycles reshape the activity of CA1 neurons to aid memory formation and how sub-layer differences contribute to this process are still unknown.
In this study, researchers examined the interactions between the anterior cingulate cortex (ACC) and hippocampal CA1 neurons during these ripple events. They discovered that learning leads to a reorganization of the communication between these two brain regions. Utilizing a statistical decoder, they confirmed that there was indeed pre-existing communication from the ACC to CA1 neurons, but this communication weakened during sleep following the learning process.
This suggests that the activity of the ACC realigns the role played by CA1 neurons in memory formation. Notably, this reorganization was unique for a subset of CA1 neurons in the superficial layer (CA1sup), which were not actively involved in the task, whereas communication between the ACC and CA1 neurons in the deeper layer remained relatively unchanged before and after training.
This selective reorganization was further evidenced by the fact that optogenetic stimulation of the ACC had different effects on these two types of CA1 neurons. It preferentially suppressed the activity of CA1sup neurons, while activating a distinct subset of CA1 interneurons that were not directly involved in the task. These findings underscore the ACC's crucial role in rebalancing the contributions of different CA1 neuronal subpopulations to the learning and consolidation of memories.
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