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人類嬰兒相對于其他物種非常的弱小，必須依靠父母的照顧才能生存下來。然而這也使得父母能學(xué)習(xí)如何照料下一代。有人認(rèn)為正是這樣成就了人類的高智商。本文表明，其實(shí)在懷孕期間，母親的大腦已經(jīng)開始發(fā)生了變化，從而讓她更能勝任母親的角色。

正文

本文選自 The Economist

譯者：倪凌暉

校對：謝曉羽

策劃：唐可可

Neuroscience 

神經(jīng)科學(xué)

Grey mater 

一孕未必傻三年

Scanning reveals what pregnancy does to a mother’s brain 

腦部掃描圖顯示，懷孕對媽媽的大腦的影響

As any parent will tell you, once you have had children nothing is ever quite the same. Including, it seems, their mothers’ brains. In a paper just published in Nature Neuroscience, a team led by Elseline Hoekzema of the Universitat Autònoma de Barcelona, in Spain, describe for the first time how pregnancy alters women’s brains, rewiring them in ways that persist long after a child has been born. 

正如任何一個父母會告訴你的那樣，懷孕會改變你的一切。這其中似乎就包括孕婦們的大腦。一個來自西班牙公立巴塞羅那自治大學(xué)（the Universitat Autònoma de Barcelona），由Elseline Hoekzema帶領(lǐng)的團(tuán)隊(duì)近期在《自然-神經(jīng)科學(xué)》（Nature Neuroscience）上發(fā)表一篇論文，首次描述了懷孕是如何改變女性大腦的，而且這種改變甚至在孩子出生后還會繼續(xù)。

Dr Hoekzema and her colleagues performed detailed brain scans on 65 female volunteers, none of whom had been pregnant before, but hoped to be in the near future, and a further 20 who had no such desire. About 15 months later, by which time 25 of their volunteers had carried babies to term, they repeated the process. 

Hoekzema教授和她的同事們對65名女性志愿者做了詳細(xì)的腦部掃描。這些志愿者沒有一個懷過孕，但希望能在近期懷孕。另外，他們還找了20名沒有懷孕意向的志愿者。大約15個月后，其中 25名志愿者成為了準(zhǔn)媽媽，并重新做了腦部掃描。

Comparing the scans showed significant reductions in the volume of grey matter in the brains of the new mothers. (Grey matter contains the main bodies of nerve cells; white matter, the brain’s other component, consists mostly of the nerve fibres that link those cells together.) The effect was reliable enough that it could be used by itself to predict, with perfect accuracy, which of the women had been pregnant and which had not. And it was persistent, too. When the researchers retested the mothers two years later, most of the alterations were still present. 

對比發(fā)現(xiàn)，新媽媽們腦中的灰質(zhì)出現(xiàn)了明顯的減少（灰質(zhì)中含有神經(jīng)細(xì)胞的主要部分，而人類大腦的另一種組成元素——白質(zhì)則大部分由鏈接神經(jīng)細(xì)胞的神經(jīng)纖維組成）。這一懷孕對女性大腦的影響相當(dāng)可靠。通過觀察灰質(zhì)減少與否，我們甚至能判斷這位女性是否懷過孕，而且不會出現(xiàn)誤判。另外，這一影響是永久性的。兩年后，研究人員對這幾位媽媽又做了一次腦部掃描，她們腦中的灰質(zhì)變化依然存在。

Dr Hoekzema and her colleagues suspected that something in the biological process of pregnancy itself was causing the changes. To double-check, and to make sure that the experience of preparing for parenthood was not the true culprit, they also compared their women’s brains with those of some men—both fathers and those without children. The men’s brains, like those of the childless women, showed no such pattern of changes. And the results fit with studies on animals. Rats that have had pups, for instance, show notable and lasting changes in brain structure. They also tend to be less anxious, better able to cope with stress, and to have better memory than their pupless contemporaries. 

Hoekzema教授和她的同事們猜測是某種在孕期生物過程中產(chǎn)生的物質(zhì)造成了這一變化。為了做再一次的檢驗(yàn)，也為了確定造成灰質(zhì)減少的主要原因不是準(zhǔn)備當(dāng)父母的經(jīng)歷，研究人員將女性志愿者的大腦與一些男性做了對比（這些男性中，一部分已經(jīng)為人父，一部分則沒有）。男性的大腦和那些沒有生育的女性一樣，并沒有出現(xiàn)灰質(zhì)的減少。而且在動物中，懷孕也產(chǎn)生了同樣的影響。例如，產(chǎn)過仔的老鼠的腦部結(jié)構(gòu)發(fā)生了顯著且永久性的變化。這些老鼠往往不那么容易緊張，應(yīng)對壓力的能力更強(qiáng)，而且與那些沒有產(chǎn)過仔的老鼠相比有更好的記憶力。

Pregnancy, then, does indeed do things to a woman’s brain. But what exactly those things mean is hard to tease out. Neuroscientists do not really understand how the brain works. That makes it difficult to predict how a change in the organ’s structure will alter the way it functions. 

懷孕確實(shí)對女性大腦產(chǎn)生了影響。但是這種影響究竟意味著什么卻并不容易搞明白。神經(jīng)系統(tǒng)科學(xué)家并不真正明白大腦是如何運(yùn)作的。這就使得我們很難預(yù)測大腦解構(gòu)的變化會怎樣影響它的運(yùn)作機(jī)能。

Some of the changes took place in the hippocampi. These are a pair of small, banana-shaped structures buried deep in the brain, one in each hemisphere, that are known to be important for forming memories. Administering a few simple cognitive tests to the new mothers—including tests of memory—revealed no obvious changes in performance. And the hippocampi had partially regrown within two years. But Dr Hoekzema and her colleagues point out that most of the more permanent reductions in grey matter happened across several parts of the brain that, in other experiments, have been found to be associated with the processing of social information, and with reasoning about other people’s states of mind. 

一些變化出現(xiàn)在海馬體中。海馬體是一對在大腦深處，香蕉形狀的小組織，左右腦各一個，負(fù)責(zé)記憶的形成。在對新媽媽們做的幾項(xiàng)認(rèn)知測驗(yàn)中，其中包括記憶測驗(yàn)，測驗(yàn)結(jié)果發(fā)現(xiàn)懷孕前后并沒有顯著變化。兩年內(nèi)，海馬體出現(xiàn)了部分再生長現(xiàn)象。但是Hoekzema教授和她的同事們指出，大部分灰質(zhì)的永久性減少出現(xiàn)在數(shù)個大腦部位。實(shí)驗(yàn)顯示，這些部位都與社交信息的處理，以及對他人心理狀態(tài)的推測有關(guān)。

That would make sense from an evolutionary point of view. Human babies are helpless, and, in order to care for one, a mother must be good at inferring what it needs. The rewiring may also affect how well women bond with their infants. After the women in Dr Hoekzema’s study had given birth, the research team administered a standard psychological test designed to measure how attached those women had become to their babies. The ones with the greatest reductions in grey- matter volume were, on the whole, the most strongly bonded. 

這一結(jié)論從進(jìn)化的角度看很合理。人類寶寶是軟弱無助的，所以為了照顧孩子，母親必須善于推測孩子需要些什么。懷孕對女性大腦的改變或許也影響了媽媽們與她們的寶寶的親密度。在這項(xiàng)研究中的媽媽們生產(chǎn)后，研究人員對她們做了標(biāo)準(zhǔn)心理測驗(yàn)，測試她們與自己的寶寶的親密度。總體來看，那些灰質(zhì)數(shù)量減少最多的媽媽與寶寶最親密。

Efficient wiring 

Ascribing all this to a reduction in grey- matter volume, rather than an increase, sounds counter-intuitive. But Dr Hoekzema reckons it is probably evidence of a process called synaptic pruning, in which little-used connections between neurons are allowed to wither away, while the most-used become stronger. That is thought to make neural circuitry more efficient, not less so. She points out that the surge of sex hormones people experience during adolescence is thought to cause a great deal of synaptic pruning, moulding a child’s brain into an adult one. So it is reasonable to assume that the even greater hormonal surge experienced during pregnancy might have a similar effect. When it comes to the brain, after all, bigger is not necessarily better. 

把所有這些都?xì)w結(jié)于灰質(zhì)的減少，而非增加，聽上去與我們的直覺相違背。但是，Hoekzema博士認(rèn)為，這或許正是一個“突觸修剪”過程。在這一過程中，那些神經(jīng)細(xì)胞間很少使用的神經(jīng)連接會被修剪，同時那些常使用的神經(jīng)連接則會連接得更緊密。人們認(rèn)為，突觸修剪會使神經(jīng)元回路變得更高效，而非更低效。她指出：在青春期階段的性激素猛增會促發(fā)大量突出修剪，從而使大腦從孩童階段進(jìn)化到成人階段。所以一個合理的假設(shè)是：孕期荷爾蒙的猛增或許也會有相同的效果。畢竟，對大腦來說，更大并不一定意味著更好。

外媒簡介

《經(jīng)濟(jì)學(xué)人》是一份由倫敦經(jīng)濟(jì)學(xué)人報紙有限公司出版的雜志，風(fēng)格機(jī)智，幽默，有力度，嚴(yán)肅又不失詼諧，并且注重于如何在最小的篇幅內(nèi)告訴讀者最多的信息。

雜志關(guān)注的新聞廣泛涉及政治、商業(yè)、金融、科技和藝術(shù)等領(lǐng)域。雜志中所有文章都不署名，但又處處用事實(shí)說話。相比較于其他國內(nèi)外語報紙，它的態(tài)度更客觀，視角更寬，在全球范圍內(nèi)的精英人士中享有獨(dú)一無二的地位。

學(xué)習(xí)筆記

【知識拓展】

【ascribable】 adj. 可歸于…的

Ascribing all this to a reduction in grey- matter volume, rather than an increase, sounds counter-intuitive.

把所有這些都?xì)w結(jié)于灰質(zhì)的減少，而非增加，聽上去與我們的直覺相違背。

【Infer】 v. 推斷；推論；推理

Human babies are helpless, and, in order to care for one, a mother must be good at inferring what it needs.

人類寶寶是軟弱無助的，所以為了照顧孩子，母親必須善于推測孩子需要些什么。

【reason about 】 沉思;思考，反省，推理

Several parts of the brain that have been found to be associated with the processing of social information, and with reasoning about other people’s states of mind.

這些大腦部位都與社交信息的處理，以及對他人心理狀態(tài)的推測有關(guān)。

【知識拓展】

【灰質(zhì)】

灰質(zhì)是一種神經(jīng)組織，是中樞神經(jīng)系統(tǒng)的重要組成部分?；屹|(zhì)由神經(jīng)元，神經(jīng)膠質(zhì)細(xì)胞，微血管組成。灰質(zhì)的灰色源于神經(jīng)元的細(xì)胞體和微血管。中樞神經(jīng)系統(tǒng)的另一個重要組成部分為白質(zhì)。

【白質(zhì)】

白質(zhì)是中樞神經(jīng)系統(tǒng)中主要的三個組成元素之一，與灰質(zhì)、黑質(zhì)并列。大腦剖面中的白質(zhì)組織是由大量的髓磷脂（脂質(zhì)）組成，在裸視觀察下呈現(xiàn)白色。 白質(zhì)由被髓鞘包覆著的神經(jīng)軸突組成，控制著神經(jīng)元共享的訊號，協(xié)調(diào)腦區(qū)之間的正常運(yùn)作。