Ample evidence has indicated a beneficial role of sleep, and particularly of slow wave sleep (SWS) in memory consolidation. However, how basic features of sleep, its depth and duration, contribute to this process remained elusive. Here, we investigated spatial object-place recognition (OPR) memory in rats, to systematically dissociate effects of sleep depth and duration on the formation of recent and remote hippocampus-dependent memory. Encoding of the spatial configuration was followed by an experimental post-encoding period of either 2 or 4 hours, during which the rats had either "regular sleep", "deeper sleep", or were kept awake. A deeper sleep was achieved by an extended habituation of the rats to the sleep environment. Retrieval was tested either immediately after the 2-hour post-encoding period (recent memory test) or 1 week later (remote memory test). Deeper sleep expressed itself in a selective increase in the time spent in SWS, and in numbers of slow oscillations, spindles, and hippocampal ripples during SWS, whereas preREM and REM sleep were not affected. At the recent test, OPR memory was preserved only after sleep, but independent of its depth. At the remote test, however, OPR memory was preserved only after deeper sleep, whereas the wake and the regularly sleeping rats did not show remote OPR memory, even with the longer 4-h post-encoding period. Our results indicate that, rather than a longer duration, deeper sleep, i.e., a longer time in SWS together with enhanced oscillatory signatures of mnemonic processing during this sleep stage, occurring within a 2-hour window after encoding, is the factor that makes hippocampus-dependent memory more persistent.

中文翻译：

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深度睡眠使海马空间记忆更加持久。

大量证据表明睡眠，尤其是慢波睡眠（SWS）在记忆巩固中的有益作用。但是，睡眠的基本特征，深度和持续时间如何影响该过程仍然难以捉摸。在这里，我们调查了大鼠的空间对象位置识别（OPR）记忆，以系统地分离睡眠深度和持续时间对近期和远程海马依赖性记忆形成的影响。在对空间配置进行编码之后，进行2或4个小时的实验性编码后阶段，在此期间，大鼠具有“正常睡眠”，“深度睡眠”或保持清醒状态。通过使大鼠长期适应睡眠环境，可以实现更深的睡眠。在编码后2小时之后立即进行检索（近期记忆体测试），或者在1周后（远程记忆体测试）进行检索。更深的睡眠表现为选择性地增加了在SWS中所花费的时间，并增加了SWS期间的缓慢振荡，纺锤体和海马波纹的数量，而REM前和REM睡眠并未受到影响。在最近的测试中，OPR内存仅在睡眠后才保留，但与深度无关。然而，在远程测试中，仅在更深的睡眠后才保留OPR记忆，而即使在较长的4小时后编码时间内，唤醒和定期睡眠的大鼠也未显示出远程OPR记忆。我们的结果表明，不是更长的睡眠时间，而是更深的睡眠，即SWS中更长的时间，以及在此睡眠阶段中助记符处理的振荡信号增强，