Why Babies Spend Most of Their Time Asleep婴儿为何睡得多

Like many other people， I’m pretty sure I don’t get enough sleep. In my case， it’s partly because my four-year-old likes to wake me up for a chat at some point between 4 a.m. and 6 a.m. on a daily basis. I’m jealous of my two-year-old， who gets a 12-hour stretch overnight and a two-hour nap in the afternoon. Oh， the luxury.

同很多人一样，我相当确信自己睡眠不足。就我而言，部分原因在于我4岁的大宝喜欢在每天凌晨4—6点的某个时刻叫醒我，和我聊天。我羡慕2岁的小宝，每晚连睡12小时，外加午睡2小时。哦，真奢侈！

Toddlers1 need more sleep than adults. And my youngest used to spend even more time sleeping. For the first couple of months of her life， it seemed she was barely awake. Scientists are still figuring out exactly why babies need so much sleep， but a new tool is starting to shed a bit more light on this mystery—and could help reveal what is going on inside the rapidly developing brain of a newborn.

学步幼儿需要的睡眠比大人要多。我的小宝过去睡得更多，她只有几个月大时，似乎就没有睡醒过。科学家仍在研究婴儿如此嗜睡的确切原因，但新的研究工具已开始进一步解开婴儿嗜睡之谜，还有助于揭示新生儿快速发育的大脑内发生了什么。

“This is a time when… the brain is developing new connections at a rate of something like a million synapses a second，” says Topun Austin， a consultant neonatologist at Cambridge University Hospitals NHS Foundation Trust in the UK. These connections are thought to play a key role in helping babies learn to make sense of the world around them. Many will later be pruned away as babies refine their understanding. But the first weeks of a baby’s life are when crucial foundations are set for life.

“新生儿时期……大脑以每秒生成约100万个突触的速度不断建立新的连接。”英国剑桥大学医院国民保健制度信托基金会的新生儿学专家顾问托蓬·奥斯汀说道。这些连接对婴儿至关重要，能帮助他们学习理解周围的世界。随着婴儿的理解不断深化，很多连接后来得以精简，但婴儿生命的最初几周会为其一生打下关键基础。

Sometimes， researchers will put a cap of EEG electrodes on a baby to study electrical brain activity. But this form of imaging doesn’t give much spatial resolution， making it hard to pinpoint exactly which brain regions are active at any one time.

有时，研究人员会给婴儿戴上有多个脑电图电极的帽子，以研究婴儿的脑电波。这种成像技术的空间分辨率不高，很难精确判定某个特定时间哪几块脑区处于活跃状态。

Others have put babies in MRI scanners that measure blood flow in the brain. If you’ve ever had an MRI scan， you can see why these hulking machines might not be the best place for a baby. They are noisy and require near-perfect stillness from the person being scanned.

另有研究人员使用核磁共振扫描仪测量婴儿的脑内血流。如果你做过核磁共振检查，你就会明白这种庞大笨重的检查仪器可能并不适合婴儿——扫描过程中不光噪音大，还要求接受扫描的人几乎一动不动。

Austin and Julie Uchitel， a former PhD student at the University of Cambridge and now a medical student at Stanford University， and their colleagues have developed a different approach. The team has used a cap with light sources and sensors embedded in it. Together， these components can meas-ure blood flow in the brain in the same way as a pulse oximeter clipped onto your finger in a doctor’s office.

奥斯汀和朱莉·乌奇捷利（曾是剑桥大学博士生，现为斯坦福大学医学生）与其他同事一起另辟蹊径，想出了新方法。该研究团队用的是一种内置光源和传感器的帽子。各种组件拼合在一起，可以测量脑内血流，方法就如同医生在诊室里给你的手指夹上一个脉搏血氧仪。

Similar techniques have been used to study the brain before， but they require the use of a cap with multiple fiber-optic cables coming out of it—not something a newborn is likely to want to sleep in. The new device makes use of recently developed tiles that each contain several light sources and detectors. Austin’s team has fitted 12 of these tiles into a cap suitable for newborns， connected to a computer with a single cable. The resulting system offers an image of the brain “at least 10 times the resolution of the previous fiber-optic cable system，” says Austin.

以前也有人用类似的技术研究过大脑，但那些技术所用的帽子连接着很多条光缆，新生儿可不愿意戴这种帽子入睡。新设备采用了最新研制出来的片材，每块片材上装有若干光源和探测器。奥斯汀团队在专为新生儿准备的帽子上安装了12块片材，只通过一根电缆将帽子与一台电脑连接。奥斯汀说，组装好的新系统扫描出的大脑影像图，“其清晰度至少是先前光缆系统的10倍”。

In a study published in the journal NeuroImage， the team asked new parents if they could monitor their babies while they were still in the postnatal ward of a hospital. “It’s like a little swimming cap—the babies seem very happy once it’s on，” says Austin. His team recorded activity from the brains of 28 newborns as they slept.

根据《神经影像》期刊上发表的一篇研究论文，奥斯汀团队询问新生儿父母，他们的孩子尚在产后病房期间，研究人员能否对孩子进行监测。“我们的帽子就像个小泳帽，一给婴儿戴上，他们就好像很开心。”奥斯汀说。他的团队记录了28个新生儿熟睡期间的大脑活动。

Babies cycle through two phases of sleep： an active phase， which is accompanied by twitching and grimacing， is followed by a quiet phase， when the baby is very still. The team filmed all the babies while their brains were monitored， so that they could later work out which phase of sleep each baby was in at any time.

婴儿的睡眠周期分为两个分期：一是活跃期，伴有身体抽动和脸部怪相；之后是安静期，此时婴儿非常安静。研究团队在监测婴儿大脑活动的同时对所有婴儿进行了摄像，以便后续确定每个婴儿在某段时间所处的睡眠分期。

Later， when Austin and his team analyzed snapshots of the recordings， they noticed differences in the brain during active and quiet sleep. During active sleep， when the babies were more fid-gety， brain regions in the left and right hemispheres seemed to fire at the same time， in the same way. This hints that new， long connections are forming all the way across the brain， says Austin. During quiet sleep， it looks as though more short connections are forming within brain regions.

后来，奥斯汀及其团队成员分析了影像记录的快照，发现大脑活动在睡眠活跃期和安静期有所不同。在活跃期，婴儿更加躁动不安，大脑左右半球的脑区似乎以同样的方式同时运转。奥斯汀说，这表明大脑各区内一直在建立新的长连接。在安静期，脑区内似乎一直在建立更多的短连接。

It’s not clear why this might be happening， but Austin has a theory. He thinks that active sleep is more important for preparing the brain to build a conscious experience2 more broadly—to recognize someone else as a person rather than a ser-ies of blobs and patches of color and texture， for example. Various brain regions need to work together to achieve this.