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(shí)開(kāi)始做夢(mèng)

    我們?yōu)槭裁醋鰤?mèng)的問(wèn)題一直難以解釋�？茖W(xué)家們已經(jīng)證明，我們需要做夢(mèng)。不讓老鼠做夢(mèng)，它們?cè)?周內(nèi)就會(huì)死亡。

    我們還知道7個(gè)月大小的胎兒也做夢(mèng)，胎兒的肌肉和眼動(dòng)能清清楚楚地反映出快速眼動(dòng)睡眠（REM）和非快速眼動(dòng)睡眠（non-REM）信號(hào)。但是，7個(gè)月之前是什么樣子呢？我們是何時(shí)開(kāi)始做夢(mèng)的？

    發(fā)表在美國(guó)物理學(xué)會(huì)《混沌》（Chaos）雜志上的研究試圖第一次給出這些問(wèn)題的答案。

    數(shù)學(xué)家分析了子宮內(nèi)15周的綿羊胎兒的腦波。對(duì)比那些難于減弱的噪音信號(hào)，這個(gè)時(shí)期的腦波信號(hào)已經(jīng)非常復(fù)雜。但是通過(guò)使用復(fù)雜的數(shù)學(xué)計(jì)算，科學(xué)家們發(fā)現(xiàn)了 一種皮質(zhì)激活和去活的模式，這種活動(dòng)每隔5到10分鐘循環(huán)一次�？茖W(xué)家們注意到，這種腦波活動(dòng)模式就是周期更長(zhǎng)的快速眼動(dòng)睡眠（REM）和非快速眼動(dòng)睡眠 （non-REM）的粗略前身。

    我們只能僅僅猜測(cè)夢(mèng)的內(nèi)容--睡夢(mèng)中會(huì)出現(xiàn)電子機(jī)器人么？但是該項(xiàng)研究表明，夢(mèng)一般的睡眠在快速眼動(dòng)之前就有了。而且該研究發(fā)現(xiàn)可能會(huì)對(duì)睡眠和夢(mèng)的目的給出新的見(jiàn)解。