Episodic memories are thought to be stabilized through the coordination of cortico–hippocampal activity during sleep. However, the timing and mechanism of this coordination remain unknown. To investigate this, we studied the relationship between hippocampal reactivation and slow-wave sleep up and down states of the retrosplenial cortex (RTC) and prefrontal cortex (PFC). We found that hippocampal reactivations are strongly correlated with specific cortical states. Reactivation occurred during sustained cortical Up states or during the transition from up to down state. Interestingly, the most prevalent interaction with memory reactivation in the hippocampus occurred during sustained up states of the PFC and RTC, while hippocampal reactivation and cortical up-to-down state transition in the RTC showed the strongest coordination. Reactivation usually occurred within 150–200 msec of a cortical Up state onset, indicating that a buildup of excitation during cortical Up state activity influences the probability of memory reactivation in CA1. Conversely, CA1 reactivation occurred 30–50 msec before the onset of a cortical down state, suggesting that memory reactivation affects down state initiation in the RTC and PFC, but the effect in the RTC was more robust. Our findings provide evidence that supports and highlights the complexity of bidirectional communication between cortical regions and the hippocampus during sleep.

中文翻译：

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睡眠期间海马记忆的重新激活与压后皮质和前额叶皮质的特定皮质状态相关

情景记忆被认为是通过睡眠期间皮质-海马活动的协调来稳定的。然而，这种协调的时间和机制仍然未知。为了研究这一点，我们研究了海马重新激活与压后皮质（RTC）和前额叶皮质（PFC）的慢波睡眠上下状态之间的关系。我们发现海马的重新激活与特定的皮质状态密切相关。重新激活发生在皮质持续向上状态期间或从向上状态过渡到向下状态期间。有趣的是，海马体与记忆重新激活最普遍的相互作用发生在 PFC 和 RTC 持续上升状态期间，而海马体重新激活和 RTC 中皮质从上到下的状态转换表现出最强的协调性。重新激活通常发生在皮质 Up 状态开始后的 150-200 毫秒内，表明皮质 Up 状态活动期间兴奋的积累会影响 CA1 中记忆重新激活的概率。相反，CA1 重新激活发生在皮质下调状态开始前 30-50 毫秒，这表明记忆重新激活会影响 RTC 和 PFC 中下调状态的启动，但 RTC 中的影响更为强劲。我们的研究结果提供了证据，支持并强调了睡眠期间皮质区域和海马体之间双向通信的复杂性。