Department of Epileptology, University of Bonn, Germany.
Cortex. 2010 Feb;46(2):256-63. doi: 10.1016/j.cortex.2009.05.012. Epub 2009 Jun 2.
Complex interactions between neocortex and hippocampus are the neural basis of memory formation. Two-step theories of memory formation suggest that initial encoding of novel information depends on the induction of rapid plasticity within the hippocampus, and is followed by a second sleep-dependent step of memory consolidation. These theories predict information flow from the neocortex into the hippocampus during waking state and in the reverse direction during sleep. However, experimental evidence that interactions between hippocampus and neocortex have a predominant direction which reverses during sleep rely on cross-correlation analysis of data from animal experiments and yielded inconsistent results. Here, we investigated directional coupling in intracranial EEG data from human subjects using a phase-modeling approach which is well suited to reveal functional interdependencies in oscillatory data. In general, we observed that the anterior hippocampus predominantly drives nearby and remote brain regions. Surprisingly, however, the influence of neocortical regions on the hippocampus significantly increased during sleep as compared to waking state. These results question the standard model of hippocampal-neocortical interactions and suggest that sleep-dependent consolidation is accomplished by an active retrieval of hippocampal information by the neocortex.
大脑新皮质和海马体之间的复杂相互作用是记忆形成的神经基础。记忆形成的两步理论表明，新信息的初步编码依赖于海马体中快速可塑性的诱导，随后是记忆巩固的第二个依赖睡眠的步骤。这些理论预测信息在清醒状态下从大脑新皮质流向海马体，而在睡眠中则相反。然而，关于海马体和大脑新皮质之间的相互作用在睡眠中具有相反主导方向的实验证据依赖于动物实验数据的互相关分析，并且产生了不一致的结果。在这里，我们使用相位建模方法研究了来自人类受试者的颅内 EEG 数据中的定向耦合，该方法非常适合揭示振荡数据中的功能相关性。一般来说，我们观察到前海马体主要驱动附近和远程脑区。然而，令人惊讶的是，与清醒状态相比，在睡眠期间，大脑新皮质区域对海马体的影响显著增加。这些结果对海马体-大脑新皮质相互作用的标准模型提出了质疑，并表明睡眠依赖性巩固是通过大脑新皮质主动检索海马体信息来完成的。
