文章来源：Science

【翻译】

怀孕能重塑女性的大脑至少两年

第一个类似研究显示，在第一次怀孕期间，妇女的大脑结构发生显著变化，这种变化至少持续2年，尤其是在涉及处理和回应社交信号区域中的灰质会收缩。这可能意味着，新妈妈的大脑在，例如回应婴儿需求或检测环境中危险人物方面更有效。这些变化与母亲对婴儿依恋程度的标准测试相关联。不管是自然怀孕还是体外受精，都有这种变化。

该研究的首席作者、荷兰莱顿大学的神经科学家Elseline Hoekzema说：“我们当然不希望在你怀孕的时候发出‘怀孕使你失去了你的大脑’这类信息。灰质体积减少也可以代表成熟或专业化的有益过程”。她同时也是一个有两岁孩子的怀孕母亲。

怀孕期是一个戏剧性的、激素驱动生理和身体变化的时期。血容量、激素水平、营养吸收和其他生理能力显着增长。根据怀孕妇女的轶事报告，一些变化没有那么有益，比如健忘和难于专注。然而对动物的研究表明，怀孕与明显的大脑结构长期变化相关联，并伴随着适应性变化，例如雌性啮齿动物变得更擅长觅食。实际上，还没有深度探讨怀孕期间人类大脑的结构变化的研究。

Hoekzema和她的同事开始着手做出改变。他们在西班牙与巴塞罗那自治大学联盟，使用磁共振成像扫描检查了未曾孕育过孩子的25名妇女的大脑。再她们分娩后3个星期到几个月内再次检查。该研究组还以相同的间隔扫描检查了19名新爸爸、17名没有孩子的男性和20名没孩子同时在研究期间也未怀孕的女性的大脑。然后，他们基于计算机的分析来测量灰质体积的变化。

研究结果高度一致显示，只在妈妈们的大脑中灰质体积减少了，这一结果报道在了今天的《自然神经科学》上。这些变化主要发生在参与社会任务的大脑区域，例如从面部和行动中读取他人的欲望和意图。与记忆相关的海马体积也减少了。另外，该小组发现，衡量妈妈对婴儿依恋程度的标准测试得分，在很大程度上可以根据怀孕期间灰质体积的变化来预测。

科学家也用MRI扫描观察了当女性看到自己婴儿和其他婴儿照片时大脑实时工作情况。相比其他婴儿照片，在怀孕期间灰质减少的几个脑区域对自己的婴儿最强烈的神经活动回应。（母亲大脑对自己的婴儿照片和其他婴儿的照片的反应比较，是研究人员用来测量对婴儿神经反应的常用方法。）

两年后，25个母亲中有11个没有再怀孕的母亲回来再进行MRI扫描。扫描结果显示，除了海马中大部分灰质体积已经恢复，其他仍保持减少后的状态。这种变化如此一致，以致计算机算法能够根据MRI扫描结果100％准确地预测一个女人是否怀孕。研究人员不能确定地解释这一结果意味着什么，因为他们不能像科学家接触啮齿类动物大脑那样研究女性大脑，但是他们推测灰质减少可能会带来适应性优势，Hoekzema说。她指出，在青春期，灰质体积的类似下降发生在当神经网络被微调以提高效率和更专业的功能时。

没有参与这项研究的科学家们指出，这项研究不仅第一次证明了怀孕人类大脑中普遍的结构变化，并且进一步表明这一变化至少持续2年。加拿大哈密尔顿的麦克马斯特大学的进化心理学家Mel Rutherford说：“它打开了可能导致育儿方式改变的可能性之门，这一改变可能对以后生活中决策和行为有潜在影响。”

他补充说，他希望在养父母和放弃子女养育的母亲中看到类似的研究。这可能增强当前研究的证据：这些变化仅仅来自怀孕这一物理事实，而不是，例如所有父母在婴儿生命早期所经历的压力和睡眠剥夺。（在目前的研究中，新父亲的大脑没有改变，尽管有这些压力。）

Abbe Macbeth是Noldus信息技术（弗吉尼亚州利斯堡的行为研究咨询公司）的神经科学家，她自己也是6岁和9岁孩子的母亲，她说：“当大脑重新构建自身以应对生活变化时，越少就是越多。”“有关于孕妇健忘的所有这些轶事，可能发生在与照顾我们的后代不需要有任何关系的区域”，她说：“这就是大自然想要我们关注的，如本文表明。”

【原文】：

Pregnancy resculpts women’s brains for atleast 2 years

A first-of-its-kind study hasrevealed that the architecture of women’s brains changes strikingly duringtheir first pregnancies, in ways that last for at least 2 years. In particular,gray matter shrinks in areas involved in processing and responding to socialsignals. This may mean that new mothers’ brains are more efficiently wired inareas that allow them, for instance, to respond to their infant’s needs or todetect threatening people in their environments. The changes correlated withstandard tests of a mother’s attachment to her infant—and they occurredwhether a woman conceived naturally or using in vitro fertilization.

“We certainly don’t want to put a messageout there along the lines of ‘pregnancy makes you lose your brain,’” says thestudy's lead author Elseline Hoekzema, a neuroscientist at Leiden Universitythe Netherlands who is also the pregnant mother of a 2-year-old. “Gray mattervolume loss can also represent a beneficial process of maturation orspecialization.”

Pregnancy is a time of dramatic,hormone-driven physiological and physical changes. Blood volume, hormonelevels, absorption of nutrients, and other physiological capabilities growdramatically. Other changes, according to anecdotal reports from pregnantwomen, are not so salubrious, like forgetfulness and difficulty concentrating.Whereas animal studies have shown that pregnancy is associated with apparentlylong-lasting anatomical brain changes—accompanied by adaptive changes, such asrodent mothers becoming better at foraging for food—virtually no studies havedrilled down on anatomical changes in the human brain during pregnancy.

Hoekzema and her colleagues set out tochange that. Working in Spain, in affiliation with the Autonomous University ofBarcelona, they used MRI scanning to examine the brains of 25 women who hadnever had children, both before they became pregnant and again from 3weeks to a few months after they gave birth. The team also scanned 19first-time fathers at the same intervals, 17 men without children, and 20 womenwithout children who did not become pregnant during the study. Then, they usedcomputer-based analyses to measure changes in gray matter volume.

The findings showed highly consistent graymatter volume losses in the mothers and not in the other groups, theteam reports today in Nature Neuroscience. The changes occurred primarilyin areas of the brain involved in social tasks like reading the desires andintentions of others from their faces and actions. The hippocampus, a regionassociated with memory, also lost volume. What’s more, the team found that themothers’ scores on a standard test that gauges the degree of a mom’s attachmentto her infant could be predicted to a significant degree based on the changesin their gray matter volume during pregnancy.

The scientists also used MRI scans to watchthe women’s brains work in real time, as they looked at photos of their owninfants and of other babies. Several of the brain areas that had lost graymatter during pregnancy responded with the strongest neural activity to theirown babies as opposed to the photos of other infants.(Comparisons between thebrain’s response to photos of a mother’s own infant and to photos of otherinfants is a common measure researchers use to gauge neural responses tobabies.)

Two years later, 11 of the 25 mothers—thosewho had not become pregnant again—returned for MRI scans. The scans showed thatgray matter loss remained—except in the hippocampus, where most volume had beenrestored. The changes were so consistent that a computer algorithm couldpredict with 100% accuracy whether a woman had been pregnant from her MRIscan.

The researchers could not explain withcertainty what the findings mean–they do not have the kind of access to thewomen’s brains that scietists have to rodents’, for instance—but they speculatethat the gray matter losses might confer an adaptive advantage, Hoekzemasays. She notes that a similar decline in gray matter volume occurs duringadolescence, when neural networks are fine-tuned for more efficiency and morespecialized functions.

Scientists not involved in the study notedthat not only is it the first to demonstrate widespread anatomical changes inthe pregnant human brain, but that it goes further by showing that the changeslast for at least 2 years. “It opens the door to the possibility that it mightcause changes in parenting that might have implications in decision-making andbehavior later in life,” says Mel Rutherford, an evolutionary psychologist atMcMaster University in Hamilton, Canada.

He adds that he would like to see similarstudies in adoptive parents and in mothers who give up their children foradoption. That might strengthen the evidence from the current study that thechanges arise solely from the physical fact of pregnancy and not, for instance,from the stress and sleep deprivation that all parents experience early in aninfant’s life. (In the current study, the brains of the new fathers did notchange despite these stresses.)

Abbe Macbeth, a neuroscientist with NoldusInformation Technology, a behavioral research consultancy in Leesburg,Virginia, and herself the mother of 6- and 9-year-olds, says that less can bemore when the brain restructures itself to respond to life changes. “There isall this anecdotal talk about pregnant women forgetting things, but that canoccur in areas that don’t necessarily have anything to do with caring for ouroffspring,” she says. “That’s what nature wants us to focus on. This papershows that.”