【经济学人】“一孕傻三年？”丨2016.12.24丨总第773期

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 ElselineHoekzema of the UniversitatAutònoma 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.

正如所有家长会告诉你的那样，一旦你有了孩子，一切都变得不一样了。似乎母亲的大脑也会发生变化。《自然-神经科学》杂志刚刚发表的一篇论文中，由Elseline Hoekzema带领的西班牙巴塞罗那自治大学的团队，首次描述了直到宝宝出生以后很久的一段时间内，怀孕是如何改变及重塑女性大脑的。

DrHoekzema 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博士和她的同事对65名女性志愿者进行详细的脑部扫描。这65名志愿者目前都没有受孕但都有近期怀孕的打算，另外还扫描了20位没有受孕打算的志愿者。大约15个月后又对已怀孕的25名志愿者进行了脑部扫描。

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. 

对比这些脑部扫描发现孕妇灰质体积明显减少。（灰质内包含神经细胞的主体；白质指大脑的其他构成成分，主要由连接神经细胞的神经纤维构成。）这一影响可以非常准确可靠地预测女性是否怀孕。并且这一影响比较持久，2年后研究人员对这些母亲进行了重新测试发现大多数孕期改变仍然存在。

• nerve fibre  神经纤维

• accuracy n.精确度

脑神经纤维束

DrHoekzema 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博士和她的同事们怀疑是怀孕的生物化过程引发了这些变化。为了复核并确保孕前准备并不是真正原因，他们还将这些女性的大脑与一些已为人父和尚未生育的男性进行了比较。这些男性的大脑同为受孕的女性一样，都没有这类变化。这个结果与动物实验的结果相吻合。例如有幼崽的白鼠的大脑结构发生了显著而持久的变化。与未受孕的白鼠相比，它们有焦虑度低，抗压力强，记忆力更好的倾向。

• Culprit  n.犯人，罪犯

• Contemporary n.当代的；同时代的人

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.

那么怀孕确实对母亲的大脑有影响。但是具体对大脑有什么影响很难弄清。神经系统科学家还未弄清大脑是如何工作的。这致使科学家很难预测器官结构的变化是如何改变其功能。

• tease out  梳理

• Neuroscientists 神经生物学家

• Structure  结构

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 DrHoekzema 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. （读者试译）

这些变化也包括海马体的变化。海马体是大脑深处分处两个半球的一对香蕉型的小组织。众所周知海马体在记忆形成方面有非常重要的作用。他们对一些新妈妈进行了一些包括记忆力测试在内的简单认知测试，测试显示她们的感知能力并没有明显的变化。并且海马体的某些部位在两年内会再生。（期待您的翻译，明天会有针对这句话的长难句解析哟~）

• Hippocampi  海马体

• Administering  执行

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 DrHoekzema’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. 

从进化的角度来看，这是有道理的。人类的婴儿是弱小的，为了照顾他们，母亲必须善于判断他们的需要。神经的重塑也可能影响母亲与新生儿的联系。参与DrHoekzema研究的女性分娩后，研究团队进行了一项标准心理测试，旨在测量这些女性对其婴儿的依恋程度。总体上，脑灰质体积减少最大的对婴儿的依恋程度最强。

Efficient wiring

高效的脑神经连接

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

将所有这一切归因于脑灰质体积的减少而不是增加听起来好像不对。但是DrHoekzema猜想这可能是突触修剪过程的证据。在突触修剪过程中神经元之间很少使用的连接逐渐萎缩，而最常用的连接则变得更强。这样可以提高而非降低脑回路的效率。她指出青少年期间性激素的激增会造成大规模的突触修剪从而将儿童的大脑塑造成成人的。因此推测怀孕期间更强的激素激增可能具有类似的效果是合理的。毕竟当谈到大脑，更大不一定意味着更好。

• synaptic pruning  突出修剪

• neurons  神经元

• hormones  荷尔蒙

翻译 ▍栏目二第五组

审核 ▍椰子

编辑 ▍毛毛