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A small protein, sometimes called the 'love hormone' might play a much wider role in how we learn to bond.

有时这种微小的蛋白质又被称为“爱情荷尔蒙”，它在我们学习如何建立亲密关系过程中可能发挥着更广泛的作用。
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When love is in the air, what's happening in the brain? For many years, biologists would answer, "Oxytocin!" This small protein — just nine amino acids long — has sometimes been called "the love hormone" because it has been implicated in pair-bonding, maternal care and other positive, love-like social behaviours.

当空气中弥漫着爱情时，大脑里正在发生什么？多年来生物学家给出的回答是：“后叶催产素”！这种微小的蛋白质——仅为9个氨基酸长度——有时又被称为“爱情荷尔蒙”，因为它与配对结合、母爱及其他建设性的、有感情特征的社会行为密切相关。

But lately, neuroscientists have been revising their thinking about oxytocin. Experiments with mice and other lab animals suggest that instead of acting as a trigger for pro-social behaviour, the molecule may simply sharpen the perception of social cues, so that mice can learn to target their social behaviour more accurately. "It turns out it’s not as simple and straightforward as 'oxytocin equals love'," says Gül Dölen, a neuroscientist at Johns Hopkins University. If something similar is true of humans, that may, among other things, add a fresh wrinkle in attempts to treat social disorders such as autism by tinkering with the oxytocin system.

但最近，神经科学家对后叶催产素的观念有所转变。老鼠及其他动物试验表明，这种分子的作用不是触发亲社会行为，而是可能提高对社交信号的感知力，这样老鼠就能学会更准确地定位社交行为。“事实证明，这并不像后叶催产素等于爱情那么简单明了”，美国约翰霍普金斯大学的神经科学家葛兰·德伦说道。如果人类也有类似的情况，那么除此以外，还能给治疗孤独症等社交障碍提供新的思路，即修复后叶催产素系统。

Neuroscientists have long believed that the release of oxytocin in the brain could be triggered by social interactions with certain individuals such as offspring or mates that are important to us and other animals. And when researchers experimentally block the action of oxytocin, mice lose the ability to recognise socially important individuals. This suggests that the molecule plays a central role in social learning — but researchers haven't known exactly how oxytocin does its job.

神经学家一直认为，与某些个体的社会交往可能触发大脑释放后叶催产素，例如对我们人类及其他动物非常重要的后代或配偶。当科学家在试验中阻止后叶催产素发挥作用时，老鼠失去了辨认重要的社交个体的能力。这表明这种分子在社交学习中发挥着核心作用——但科学家尚不清楚后叶催产素究竟是如何做到的。

That is changing, thanks to advances in neuroscience techniques, which in recent years have allowed researchers to identify and record the activity of individual oxytocin-producing neurons deep within the brain. And those recordings tell a story that differs from the old view — in subtle but important ways.

得益于神经科学技术的进步，这种境况正在得到改善，近年来科学家能够识别和记录大脑深处的个体神经元释放后叶催产素的活动，记录的情形与传统观点之间有重要的细微差异。

In the main smell centre of rats' brains, for example, measurements show that oxytocin inhibits the random, noisy firing of nerve cells, thus allowing the neural signals of actual odours to stand out more prominently. (It does this in a backhanded way, by exciting nerve cells known as granule cells, which inhibit other nerve cells.)

以老鼠的嗅觉中枢为例，测量结果显示后叶催产素抑制神经元随意传递嘈杂的信号，这样能使真正气味的神经信号更为突出（后叶催产素是以间接的方式做到的，它刺激被称为粒细胞的神经元，而粒细胞能抑制其他神经元）。

Like tuning in to the sound of your child, oxytocin might help our brains to focus on the most important signals – cutting out noise

正如听到自己孩子的声音一般，后叶催产素可能帮助我们的大脑关注最重要的信号——滤掉噪音。
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Robert Froemke, a neuroscientist at New York University Grossman School of Medicine and Young's coauthor, uses hearing his baby crying over background noise as an analogy to the clarity oxytocin creates in our brain. "I've got two little kids," he says. "Even two rooms away, air conditioner on, and I'm deep asleep, the baby starts crying and right away I'm awake and attending, full-pupil-dilated."

罗伯特·弗罗姆克是纽约大学格罗斯曼医学院的神经科学家，他把后叶催产素在大脑中创造的清晰环境比作从背景噪声中听到婴儿的啼哭声。“我有两个孩子”，他说道。“即使相隔两个房间，空调开着，我在熟睡，当婴儿开始啼哭时，我马上就醒了，专注声音，瞳孔放大”。

Oxytocin also enhances the response of the brain's reward system, says Yevgenia Kozorovitskiy, a neuroscientist at Northwestern University. This effect could shift the animal's behaviour away from seeking out new things in the environment, and toward focusing on social rewards.

后叶催产素还能强化大脑的奖赏系统，来自美国西北大学的神经科学家叶夫吉尼亚·科佐罗维茨基说道。这种效应可能使动物避免在环境中物色新事物，并专注于社交奖赏。
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In prairie voles, for example — which intrigue researchers for their monogamous behaviour, rare in rodents — this shift facilitates pair-bonding. Among other effects, some of the oxytocin-sensitive cells lix a mate's odour to the reward system. "Pair-bonding is kind of like becoming addicted to a partner," says Young. "The partner becomes inherently rewarding." Promiscuous species such as mice and meadow voles lack those oxytocin receptors but, tantalisingly, they're there in the brains of people, suggesting that we may respond more like prairie voles than mice. (Oxytocin's molecular cousin, vasopressin, also plays a role in pair-bonding.)

以草原田鼠为例，它们一夫一妻制的行为激起了科学家的兴趣，这种行为在啮齿动物中罕见——这有利于配对结合。除了其他效应以外，某些对后叶催产素敏感的细胞将配偶的气味与奖赏系统相关联。“配对结合有点类似于对配偶上瘾”，杨先生说道。“配偶本身成为奖赏”。老鼠、普通田鼠等滥交物种缺少后叶催产素受体，但可喜的是存在于人类大脑中，这表明我们的反应可能更像草原田鼠，而不是老鼠。（与后叶催产素有关的分子后叶加压素在配对结合中也发挥着作用）。

Like some species of vole, pair-bonding might make us 'addicted' to our partners, reducing promiscuous behaviours

正如某些种类的田鼠，结合配对可能使我们对伴侣“上瘾”，减少滥交行为。

There's a further complication here, and an important one: If oxytocin's real role is to clarify social-related sensory perceptions, not simply to promote sociality, then the chemical is likely to have different effects in different contexts. For example, Young notes, oxytocin enhances maternal care in mice — clearly a pro-social behaviour — but it also increases maternal aggression toward unfamiliar individuals.

这里还有一个复杂的问题，并且很重要：如果后叶催产素的真正作用是净化与社交有关的感官知觉，而不只是促进对社交的向往，那么后叶催产素在不同的环境下可能产生不同的效应。例如杨先生指出，后叶催产素能增强老鼠的母性——这是明显的亲社会行为——但也增加了对陌生个体的母性攻击行为。

Moreover, female prairie voles respond differently to oxytocin depending on whether they have formed a pair bond yet, Young and his colleagues have found. In unbonded females, oxytocin reduces noise in the reward system, allowing them to learn to like a potential partner's odour. In females that have already bonded with a partner, the molecule turns up the volume on the reward system to make the partner more rewarding, thus reducing aggression toward the partner.

另外，杨先生及其同事发现，雌性草原田鼠对后叶催产素有不同的反应，这取决于它们是否拥有伴侣。在没有伴侣的雌性中，后叶催产素减少奖赏系统的噪音，使它们学着喜欢上某只潜在伴侣的气味。在已拥有伴侣的雌性中，后叶催产素增大奖赏系统的音量，使伴侣更有价值，从而减少对伴侣的攻击行为。

Something similar may apply to people, too. In one study from 2012, 30 men who were in monogamous relationships maintained a slightly greater social distance from an attractive female stranger when they received an intranasal oxytocin spray than when they got a placebo. The effect wasn't seen in a similar group of 27 single men.

人类可能也有类似的情况。在2012年的一项研究中，30名男性在接受催产素鼻喷雾剂后，与接受安慰剂相比，他们与陌生美女保持的社交距离更远一些。这种效应在27名单身男性组中没有出现。

The context-dependence of oxytocin may complicate efforts to use oxytocin to treat autism-spectrum disorder. Some therapists already use intranasal oxytocin sprays to treat people with autism, on the theory that it should enhance their response to social stimuli. However, a large clinical trial recently found no demonstrable effect.

后叶催产素有赖于环境，利用它治疗孤独症谱系障碍可能因此变得复杂。有些医疗专家已经利用催产素鼻喷雾剂治疗孤独症患者，理论依据是应该能增强患者对社交刺激的反应。但是，最近开展的大规模临床试验并未发现显著疗效。

That's not surprising, Young says, because the trial did not control the context in which patients received the sprays. If a child is being bullied at school, for example, the proposed treatment might not help but instead might intensify that negative experience, he notes. Instead, Young thinks that any oxytocin-based therapies would need to be carefully delivered in the safety of a therapy session.

这并不奇怪，杨先生说道，因为该试验没有控制患者接受喷雾剂治疗的环境。例如，如果孩子在学校受欺负了，该疗法可能无济于事，反而强化负面经历。杨先生认为，任何催产素类疗法都需要在疗程安全的情况下谨慎实施。

Neuroscientists also note that even though oxytocin clearly plays an important role in regulating social behaviors like pair-bonding and parental care, it's not the only actor. "Falling in love is a full brain and body experience," says Kozorovitskiy. "It has sensory elements and cognitive elements, and memory is important. Is oxytocin one of the many modulators that is mediating all those changes? Absolutely. But can we pin it all on oxytocin? That's definitely an oversimplification."

神经科学家也指出，尽管后叶催产素在调节配对结合、母爱等社交行为方面明显发挥着重要作用，但它不是唯一的因素。“坠入爱河是全身心的体验”，科佐罗维茨基说道。“爱情涉及感官和认知因素，回忆很重要。后叶催产素是调节这一切变化的因素之一吗？确实是。但我们能把爱情完全归因于后叶催产素吗？那肯定是过于简单化了。