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.

　　而另一組受控志愿者在早上學習，晚上測試，中間沒有睡眠，研究人員發現這種學習效果差強人意。而對睡眠人員的腦電波進行監測后發現，相較于睡眠淺的志愿者，睡眠較深的志愿者的新增記憶得到了更有效的鞏固。

　　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.

　　這些研究結果突出了睡眠的重要性，并解釋了擴充詞匯量的腦部機制。研究論文主要撰稿人Jakke Tamminen稱：“如果你能將新增記憶和自己已有的知識儲備聯系起來，新增記憶才算真正有用。”他還說他們的研究證實了人們在睡覺時大腦組織新記憶并將其與已有知識聯系起來。