Why we dream continues to elude us. Scientists have proven we need to dream. When robbed of their dreams, rats die within four weeks.

    We also know that at seven months a fetus is dreaming, its muscles and eye movements giving the tell-tale signs of REM （or rapid eye movement） sleep and non-REM sleep. But what happens before seven months? When do our dreams begin?

    Research published in Chaos, a journal of The American Institute of Physics, provides the first attempt at an answer.

    Mathematicians analyzed the brainwaves of a fetal sheep in utero, at 15-weeks. The brain signals at that stage are quite complex, set against noise that is difficult to dampen. But using sophisticated mathematics, scientists discerned a pattern of cortical activation and deactivation, cycling every five to ten minutes - this, the scientists note, is a crude precursor to the longer cycles of REM and non-REM sleep.

    We can only guess at the content-do sleep dream of electric androids? But the study shows that dreamlike sleep develops before rapid eye movements. And the discovery may give researchers new insight into the purpose of sleep and dreams.

    我們何時開始做夢

    我們為什么做夢的問題一直難以解釋。科學家們已經證明，我們需要做夢。不讓老鼠做夢，它們在4周內就會死亡。

    我們還知道7個月大小的胎兒也做夢，胎兒的肌肉和眼動能清清楚楚地反映出快速眼動睡眠（REM）和非快速眼動睡眠（non-REM）信號。但是，7個月之前是什么樣子呢？我們是何時開始做夢的？

    發表在美國物理學會《混沌》（Chaos）雜志上的研究試圖第一次給出這些問題的答案。

    數學家分析了子宮內15周的綿羊胎兒的腦波。對比那些難于減弱的噪音信號，這個時期的腦波信號已經非常復雜。但是通過使用復雜的數學計算，科學家們發現了 一種皮質激活和去活的模式，這種活動每隔5到10分鐘循環一次。科學家們注意到，這種腦波活動模式就是周期更長的快速眼動睡眠（REM）和非快速眼動睡眠 （non-REM）的粗略前身。

    我們只能僅僅猜測夢的內容--睡夢中會出現電子機器人么？但是該項研究表明，夢一般的睡眠在快速眼動之前就有了。而且該研究發現可能會對睡眠和夢的目的給出新的見解。