Kyra DeBlaker-Gebhard is normally an ace at keeping track of special occasions. But since she's been pregnant, "I can't remember a birthday, a graduation or an anniversary," laments the 30-year-old Washington, D.C., writer.

Her communication skills have also taken a plunge: "Especially in my first trimester, I had a very difficult time speaking coherently and writing clearly," she says.

DeBlaker-Gebhard is far from alone: Between 50 percent and 80 percent of pregnant women report memory and thinking problems during this time.

"Until I finally talked to a friend about it, I thought it was just me," DeBlaker-Gebhard says.

Recently, researchers have been examining whether this phenomenon—dubbed "baby brain"—has an objective basis. It's part of a recent wave of research looking at how pregnancy and motherhood affect women cognitively, a different slant from previous research that has focused on brain areas and processes that more directly influence females' propensity to nurture their young.

The findings suggest an intriguing picture that is good news for anyone embarking on the adventure of motherhood, notes University of Richmond neuroscientist Craig Kinsley, PhD, a main researcher in the area. Pregnant women do in fact experience a physiologically based baby brain, the likely result of a hormone flood that peaks in the third trimester as well as possible external factors, such as a more chaotic life during pregnancy, studies are showing. But related research finds that once the women give birth, other brain mechanisms kick in that help them protect their young by bolstering their cognitive abilities, and these benefits may last into old age.

"There is a tendency to see pregnancy and lactation as somewhat debilitating conditions," says Kinsley. "However, when it comes to motherhood, we're looking at changes that are beneficial to the female, and for the majority of her life."

Support for 'baby brain'

In the most stark evidence that the baby brain phenomenon is real, research has found that the brain actually shrinks a little during pregnancy. In a study reported in the January 2002 American Journal of Neuroradiology, Angela Oatridge, PhD, of Hammersmith Hospital in London, and colleagues found that women's brain volume diminished by about 4 percent during pregnancy, then returned to normal after delivery. Similarly, a study reported in the February 2000 Hormones and Behavior (Vol. 37, No. 1) by neuroscientist Liisa Galea, PhD, of the University of British Columbia, found that the volume of the hippocampus—a key center for memory and spatial learning—was smaller in pregnant rats than in nonpregnant rats.

In other studies, Galea showed that rats in their third week of pregnancy—the equivalent of the first human trimester, when levels of progesterone, estradiol, prolactin and related hormones are at their peak—showed decreased spatial learning ability compared with nonpregnant rats, an effect others have found during the early postpartum period as well.

Galea also has been studying new nerve growth in the hippocampus, both in pregnant rats and in rat mothers, known as dams. It's an intriguing area of study, she says, because the hippocampus is noted for its ability to generate new nerve cells throughout adulthood. Interestingly, she found no differences in nerve-cell growth in pregnant rats compared with virgin rats, and much lower levels in rat dams during the early postpartum period.

The findings suggest that on the biological level, pregnancy and the early postpartum period "are almost like a down time," Galea says. "Given that hormone levels rise to at least 1,000 times their normal levels during the third trimester, then plunge around birth, it's not surprising that some things get muddled in that hormonal soup."

In humans, it is difficult to study such brain and nerve-cell changes. As a result, researchers who study pregnant women generally focus on the women's performance on cognitive and memory tasks—important, they say because people are often notoriously inaccurate when it comes to assessing their memory abilities. So far, they've found that just as in rats, pregnant women perform worse on some learning and memory tasks than nonpregnant controls.

For example, in a meta-analysis of studies on pregnant women and memory functioning reported in the November 2007 Journal of Clinical and Experimental Neuropsychology (Vol. 29, No. 8), psychologists Julie Henry, PhD, of the University of New South Wales, and Peter G. Rendell, PhD, of Australian Catholic University, found a pattern: Pregnant women across all trimesters performed slightly worse than matched nonpregnant controls on memory tasks that impose particular demands on executive functioning, which encompasses higher-level thinking processes for creating and actualizing goals. Those effects lasted up to a year postpartum, they found.

In another study, the team examined how pregnancy affects prospective memory—our ability to remember to perform intended future actions, such as taking medicine at a particular time—known to be highly sensitive to failures in executive control. Pregnancy researchers are particularly interested in studying prospective memory because it is susceptible to real-life distractions, to which pregnant women and new mothers are especially vulnerable to, the researchers note.

In the study, published online March 14 and now in press at the Journal of Clinical and Experimental Neuropsychology, Rendell and Henry compared women in their third trimesters with controls on two types of prospective memory tasks, one in the lab and one in the field. The tasks were similar in that each combined aspects of real-life functioning and a lab-test paradigm. The lab test was a board game called "Virtual Life," which required participants to make choices about daily activities and remember to carry out lifelike tasks, while the field task required women to remember from home to push a button and log in the time at prescribed times over seven days.

Although the two groups performed equally well on the lab tests, pregnant women did significantly worse than controls on remembering to follow through on the field task.

In a related, as-yet-unpublished study, University of British Columbia doctoral student Carrie Cuttler, UBC Psychology Professor Peter Graf, Galea and UBC postdoctoral fellow Jodi Pawluski, PhD, compared 61 women in all three trimesters of pregnancy and 24 nonpregnant controls on lab and field measures of prospective memory. Again, the women did equally well on the lab tests, but women in the first trimester did significantly worse than others on the field-based prospective memory task.

Though it's unclear why the two studies found differences in the stage at which women were most affected, both suggest that lifestyle factors may be exacerbating a subtle underlying deficit, the researchers agree.

"We have a hard time finding these problems when pregnant women are in a distraction-free, sterile lab environment," says Cuttler. "But when women are in their everyday lives and they're dealing with all of these competing demands—their husbands and children pulling them this way, their work pulling them another way—that's when you see these deficits."

Findings on older adults underscore the point, notes Rendell. In other studies, he has found that older adults—who often have more structured, familiar routines compared to younger adults—tend to perform well on real-life prospective-memory tasks, but worse on lab tests.

"These differences suggest that lifestyle is working to support older adults and challenge the pregnant women," he says.

Motherhood as the fix?

After delivery, though, these deficits appear to reverse, at least in animals. In a paper in the February Archives of Sexual Behavior, (Vol. 37, No. 1), the University of Richmond's Kinsley summarizes a decade of work that he, his students and others have done showing that mother rats, monkeys and even beetles perform better on learning, memory and cognition tasks than nonmothers. His lab also has found brain and nerve-growth correlates for some of these phenomena. (Kinsley was the first to show that motherhood enhances spatial learning and memory in rat dams.)

Over time, Kinsley and others have tested two evolution-based hypotheses on why mothers may develop new cognitive and memory skills. One is that their brains and hormones change to enhance their abilities to fend off predators, leave the nest to find food and return quickly so their young aren't attacked. The other theory is that these changes reduce the mothers' fear and anxiety so they can better face such challenges.

"We and other labs have found a lot of support for both," Kinsley says. As a recent example bolstering the first hypothesis, an unpublished study by Kinsley's students Naomi Hester, Nathalie Karp and Angela Orthmeyer found that over three trials, mother rats were five times faster than virgin rats at catching crickets. Meanwhile, researchers including Inga Neumann, PhD, of the University of Regensburg in Germany have shown that pregnant and lactating rats are less prone to fear and anxiety in the face of stress than virgin rats, as measured by fewer stress hormones in the blood.

Kinsley's team is now looking into other ways animals' physiology may change to accommodate motherhood, such as improved blood flow and motor skills. Like Galea, Kinsley has also looked at nerve growth in the hippocampus of pregnant, mother and virgin rats. He found an increase in dendritic spines on neurons in an area that regulates some types of learning in pregnant and mother rats compared with virgin rats, he says.

Pawluski and Galea are seeing a more mixed picture. They find decreased dendritic branching in the hippocampus in first-time dams at the time of weaning and more dendritic spines in second-time moms. But on behavioral measures, rat moms perform significantly better on spatial working memory tests than nonpregnant rats, with first-time moms performing the best of all.

One potential explanation for those contradictory findings is that the enhanced learning in first-time dams may be partially caused by stress hormones, which tend to be higher in pregnancy and especially in first-time mothers. In addition, the team has not yet looked at nerve-cell growth in dams that have had more than one pup, Galea says. It is also possible that the "nerve pruning" that takes place during motherhood actually benefits spatial learning, she speculates.

Later rewards

Meanwhile, Kinsley's lab is also looking at the brains of rat moms that are past bearing age to see if earlier benefits accrue into older age. In a study headed by Kinsley's student Jessica D. Gatewood, reported in the July 2005 Brain Research Bulletin (Vol. 66, No. 2), the team found that at 24 months—the equivalent of a person's mid-80s—mother rats were better at learning spatial tasks and showed less memory decline than age-matched rats that were never pregnant.

In examining the older dams' brains on autopsy, the team also found significantly reduced levels of immunoreactive amyloid precursor protein, a marker of neurodegeneration and age-related cognitive decline, including Alzheimer's disease, Kinsley says.

For him, such changes suggest a place for motherhood alongside other natural developmental periods such as sexual differentiation, puberty and menopause.

"This is another epoch in a female's life," he says. "The brain changes are as dramatic as what you see during the other phases."

来自华盛顿的Kyra DeBlaker-Gebhard是个30岁的作家，她总是能记住一些特别的日子。不过从她怀孕之后，就再也不记得任何生日、毕业或者结婚纪念日了。

她的沟通能力也受到了影响：“尤其是头三个月，我很难有条理地说清楚一件事或者写东西。”

DeBlaker-Gebhard的问题并不少见：50-80%的孕妇报告说自己会在怀孕期间记不住事情或者反应迟钝。

“在我和一个朋友说起这件事情之前，我一直以为就我是这样。”DeBlaker-Gebhard说。

最近，研究者们正在研究这个被称之为“婴儿脑”的现象，是否有着生理基础。最近这股研究养儿育女如何从认知上对女性产生影响的热潮有别于之前的研究，之前的研究更着重在脑区和大脑思维过程，那些能够更直接影响女性哺育幼儿行为的因素上。

雷蒙德大学的神经学家Graig Kinsley博士是这一研究领域的重要人物，他说这些研究发现对于那些即将成为母亲的女性来说，无疑是个好消息。研究显示，孕妇的确会经历一段有着生理基础的“婴儿脑”时期，这很可能是由于在最后三个月荷尔蒙的急剧攀升，或者潜在的外在因素，比如孕期混乱的生活状态造成的。不过相关的研究还发现，在分娩之后，为了保护新生儿，脑机制也调动起来支持辅助认知能力，而这些益处会一直持续到很久之后。

“有人将怀孕和哺乳是一个虚弱的情况，”Kinsley说，“不过，说道当母亲，我们在寻找那些有益于女性、并对她以后的生活有帮助的变化。”

“婴儿脑”的支持者

支持“婴儿脑”现象最有力的证据是，研究发现大脑的确会在怀孕期间有所变化。一项在2002年一月的《美国神经放射学杂志》上发表的研究中，伦敦Hammersmith医院的Angela Oatridge博士和同事们发现，妇女的脑容量在怀孕期间会降低4%，并在分娩之后恢复原有水平。而在一项2000年2月《荷尔蒙与行为》杂志上发表的研究中，UBC的神经学家Liisa Galea博士则发现，怀孕的大鼠的海马体（记忆和空间认知的中心区域）的体积比没有怀孕的大鼠的小。

在另外一些研究中，Galea发现大鼠在怀孕的第三周（相当于人类怀孕的前三个月），也就是孕酮、雌二醇、催乳素和其他相关激素到达峰值的时候，它们在空间学习能力上出现衰退，这一现象也曾在产后早期被发现。

Gelea还研究了怀孕的大鼠和生产过的大鼠海马体中新神经的发育情况。她说这是一项很有深意的研究，因为海马体对于成年期新神经细胞的生长很重要。有趣的，她并没有发现怀孕的大鼠和没有交配过的大鼠之间神经细胞的发育有什么不同，但是生产后的大鼠在分娩后早期，神经细胞的发育水平却非常低。

这些研究结果说明在生理层面，怀孕及产后早期是“最低潮的”。Galea说：“由于荷尔蒙水平在怀孕最后三个月会飙升到正常的1000倍以上，而在分娩前后出现暴跌，那么有些事情在荷尔蒙的过分冲击被扰乱就不让人奇怪了。”

我们很难在人类身上研究这样的大脑和神经细胞变化。因此，对于孕妇的研究一般集中在女性在认知和记忆任务的表现上，这很重要，因为众所周知，如果测试记忆能力，人们的反映往往并不可靠。到目前位置，他们发现，就和大鼠一样，和没有怀孕的对照组相比，怀孕的女性在某些学习和记忆任务中的表象更糟。

比如，在2007年《临床和实验神经心理学》杂志上发表的一项孕妇和记忆的综述分析中，新南威尔士大学的心理学家Julie Henry博士和澳大利亚天主教大学的Peter Rendell博士发现了这样一个规律：处于不同怀孕阶段的女性在记忆任务中都比没有怀孕的控制组表现稍差，尤其是那些执行性任务。包括了创立和达成目标这样的高级思维过程。他们发现，这些影响一直会持续到产后一年。

在另一项研究中，这个研究团队还检查了怀孕对于预测性记忆的关系，预测性记忆也就是我们能不能记住以后将要做哪些事情的能力，比方说能否准时吃药，这种记忆被认为对于执行任务操控非常敏感。对于怀孕的研究游戏对于执行性记忆感兴趣的原因在于这与现实生活的心不在焉极为相似，而这是怀孕的女性和新妈妈们最容易面对的问题。

3月14日在线发表的《临床与实验神经心理学杂志》的一项研究中，Rendell和Henry让怀孕末三个月的女性和对照组进行了两项执行性记忆任务，一项是在实验室内进行，另外一项则是实际生活的场景。这两项任务的共同支出在于各自都将现实生活中的场景和实验场景结合起来。实验室实验用的是一款叫做“虚拟人生”的桌面游戏，这个游戏要求参与者对于日常活动进行选择，还要记住要做哪些模拟现实的任务，而场地实验则要求女性参与者们记住连续7天在规定的时间家里要按一个钮并进行登陆。

虽然两组在实验室测试中表现基本相同，但是怀孕的女性在场地实验中的表现明显比对照组差。

在一项相关的、但尚未发表的研究中，UBC的博士生Carrie Cuttler，心理学教授Peter Graf, Galea，以及博士后Jodi Pawluski使用了61怀孕阶段不同的女性以及24名没有怀孕的对照组女性，对于他们执行性记忆进行了实验室以及场地比较实验。实验再一次发现，这些女性在实验室测试中表现详单，但是怀孕前三个月的女性在执行性记忆的场地实验中的表现明显不佳。

虽然还不清楚为什么这两项试验发现最受影响的怀孕阶段不一样，不过还是指出生活方式可能会夸大那些不太明显的潜在区别。

“如果让她们呆在一个没有干扰、静态的实验室环境中，我们可能很难倒找什么不同。”Cuttler说，“不过处于日常生活中的女性，每天都要处理很多可能冲突的事情，他们的丈夫和孩子向这边拽他们，而工作则又把他们拽向另一边，这时候矛盾就出现了。”

Rendell还指出，年龄较大的成年人出现相反的结果。在其他的实验中，他发现年龄较长的成人，他们的生活比起年轻人来说往往有一套更系统、习惯的程序，他们在场地实验中表现得不错，但是在实验室测试中的表现则不佳。

他说：“这些差异说明生活方式对年龄较大的人起到了支持的作用，而对孕妇则是个挑战。”

当妈就能解决问题？

不过在分娩之后，这些矛盾开始发生逆转，起码在动物身上是如此。在二月号的《性行为档案》杂志中，Richmond大学的Kinsley总结了过去十年中自己、学生和其他人的研究，发现当了妈妈的大鼠、猴子甚至甲壳虫比起那些没当妈的，在学习、以及和认知任务中的表现都要更好。他的实验室还发现大脑和神经的发育于这些现象中的一些有关联（Kinsley是第一个发现当妈对于大鼠的空间学习和记忆有促进作用的人）。

长久以来，Kinsley和其他一些人一直在验证两个基于进化学的假设，一直都在试图解释为什么母亲们可能会产生一些新的认知能力。其中一个假设是雌性的大脑和荷尔蒙发生变化，使得他们抵御天敌的能力加强、它们可以离开巢穴觅食后更快地回到孩子身边，以避免受到攻击。另一个理论是这些变化降低了母亲的恐惧和焦虑，使得她们可以更好地面对挑战。

“我们和其他实验室都发现了很多支持这两个观点的证据。”Kinsley说。最近的一个例子就支持了第一种观点，由Kinsley的学生Naomi Hester, Nathalie Karp 和Angela Orthmeyer进行的一项未发表研究中，他们通过三轮实验发现，大鼠妈妈捉板球的速度比未曾交配的大鼠快5倍。与此同时，包括德国 Regensburg大学的Inga Neumann博士在内的研究人员也通过测量血液中的压力荷尔蒙，发现怀孕和哺乳期的大鼠在面对压力时，比未曾交配的大鼠更少出现恐惧和焦虑。

Kinsley的团队现在正在寻找动物体内与成为母亲有关的其他生理变化，比如血流量增加和运动能力提高。和Galea一样，Kinsley也检查了未交配、怀孕、产仔的大鼠海马体内神经的发展情况。他发现在一个控制学习的脑区中，比起未交配的大鼠，怀孕和产仔的大鼠神经细胞树突有所增加。

Pawluski和Galea考察的是更固定的内同。他们发现第一次产仔的大鼠在断奶的时候，海马体中的树突有所减少，而在第二次产仔的大鼠中则有所增加。但是在行为测量的维度，产仔的大鼠在空间工作记忆测试中的表现明显好过没有怀孕的老鼠，而第一次产仔的大鼠表现最好。

对于这些矛盾的发现，一种可能的解释是，初次产仔的大鼠学习能力则提高可能一部分是因为压力荷尔蒙，在怀孕、尤其是在第一次怀孕的大鼠中，这种荷尔蒙的浓度更高。另外，研究队伍还没有对于神经细胞的生长进行过多的研究。另一种可能是，这种这种发生在产仔之后的“神经修剪”，实际上对于空间学习有好处。

延迟的奖励

同事，Kinsley的实验室还研究了过了繁殖期的产过仔的大鼠，研究它们的大脑来看看早期的好处会不会持续要以后。在一项由Kinsley的学生Jessica D. Gatewood主持、发表于2005年7月《脑研究学报》的研究中，他们发现在24个月的时候（相当于人类80多岁），曾经产仔的雌性大鼠比那些同样年纪、但从未交配的大鼠具有能耗的空间学习能力，记忆的减退也较少。

在对于老龄雌鼠的大脑做的解剖检查中，研究团队还发现免疫交互淀粉样前体蛋白质（immunoreactive amyloid precursor protein），一种可以标记包括阿尔海默症在内的神经退行性病变以及认知衰老的标志物，在产过仔的雌鼠脑中含量显著较低。

对于Kinsley来说，这种变化意味着成为母亲，和其他自然发育过程，比如性别分化、青春期、更年期有同等的地位。

“这是女性生命中另一个里程碑，”她说，“大脑发生的变化就像你在其他关键阶段看到变化一样的剧烈。”

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