This did not occur in a control group of volunteers who were trained in the morning and re-tested in the evening, with no sleep in between. An examination of the sleep volunteers' brainwaves showed that deep sleep (slow-wave sleep) rather than rapid eye movement (REM) sleep or light sleep helped in strengthening the new memories.

　　而另一组受控志愿者在早上学习，晚上测试，中间没有睡眠，研究人员发现这种学习效果差强人意。而对睡眠人员的脑电波进行监测后发现，相较于睡眠浅的志愿者，睡眠较深的志愿者的新增记忆得到了更有效的巩固。

　　These results highlight the importance of sleep and the underlying brain processes for expanding vocabulary. Lead author Jakke Tamminen, said: "New memories are only really useful if you can connect them to information you already know." he said their study identifies the brain activity during sleep that organizes new memories and makes those vital connections with existing knowledge.

　　这些研究结果突出了睡眠的重要性，并解释了扩充词汇量的脑部机制。研究论文主要撰稿人Jakke Tamminen称：“如果你能将新增记忆和自己已有的知识储备联系起来，新增记忆才算真正有用。”他还说他们的研究证实了人们在睡觉时大脑组织新记忆并将其与已有知识联系起来。