Department of Psychology, Sapienza University of Rome, Roma, Italy.
Neuroimage. 2012 Mar;60(1):497-504. doi: 10.1016/j.neuroimage.2011.11.093. Epub 2011 Dec 8.
Converging data that attribute a central role to sleep in memory consolidation have increased the interest to understand the characteristics of the hippocampal sleep and their relations with the processing of new information. Neural synchronization between different brain regions is thought to be implicated in long-term memory consolidation by facilitating neural communication and by promoting neural plasticity. However, the majority of studies have focused their interest on intra-hippocampal, rhinal-hippocampal or cortico-hippocampal synchronization, while inter-hemispheric synchronization has been so far neglected. To clarify the features of spontaneous human hippocampal activity and to investigate inter-hemispheric hippocampal synchronization across vigilance states, pre-sleep wakefulness and nighttime sleep were recorded from right and left homologous hippocampal loci using stereo-EEG techniques. Hence, quantitative and inter-hemispheric coherence analyses of hippocampal activity across sleep and waking states were carried out. The results showed the presence of delta activity in human hippocampal spontaneous EEG also during wakefulness. The activity in the delta range exhibited a peculiar bimodal distribution, namely a low frequency non-oscillatory activity (up to 2 Hz) synchronized between hemispheres mainly during wake and REM sleep, and a faster oscillatory rhythm (2-4 Hz). The latter was less synchronized between the hippocampi and seemed reminiscent of animal RSA (rhythmic slow activity). Notably, the low-delta activity showed high inter-hemispheric hippocampal coherence during REM sleep and, to a lesser extent, during wakefulness, paralleled by a (unexpected) decrease of coherence during NREM sleep. Therefore, low-delta hippocampal state-dependent synchronization starkly contrasts with neocortical behavior in the same frequency range. Further studies might shed light on the role of these low frequency rhythms in the encoding processes during wakefulness and in the consolidation processes during subsequent sleep.
将睡眠在记忆巩固中起核心作用的数据汇集在一起，增加了人们理解海马睡眠特征及其与新信息处理关系的兴趣。不同脑区之间的神经同步被认为通过促进神经通讯和促进神经可塑性而参与长期记忆巩固。然而，大多数研究都集中在海马内、海洛因海马或皮质海马同步上，而半球间同步至今仍被忽视。为了阐明人类海马自发活动的特征，并研究睡眠和清醒状态下半球间海马同步，使用立体脑电图技术从右和左同源海马位置记录了预睡眠觉醒和夜间睡眠的海马活动。因此，对睡眠和清醒状态下海马活动进行了定量和半球间相干性分析。结果表明，在清醒状态下，人类海马自发脑电图中也存在δ 活动。δ 频段的活动表现出一种特殊的双峰分布，即半球间同步的低频非振荡活动（最高 2 Hz）主要发生在清醒和 REM 睡眠期间，以及更快的振荡节律（2-4 Hz）。后者在海马之间的同步性较低，类似于动物 RSA（节律性慢波活动）。值得注意的是，在 REM 睡眠期间，低 δ 活动表现出高半球间海马相干性，在清醒时则较低，但在 NREM 睡眠期间相干性下降（出乎意料）。因此，低 δ 海马状态依赖性同步与同一频率范围内的新皮层行为形成鲜明对比。进一步的研究可能会揭示这些低频节律在清醒时的编码过程和随后睡眠时的巩固过程中的作用。
