麻醉药帮助我们理解什么是意识

More than a decade ago, a 43-year-old woman went to a surgeon for a hysterectomy. She was put under, and everything seemed to be going according to plan, until, for a horrible interval, her anesthesia stopped working. She couldn't open her eyes or move her fingers. She tried to breathe, but even that most basic reflex didn't seem to work; a tube was lodged in her throat. She was awake and aware on the operating table, but frozen and unable to tell anyone what was happening.
十多年前的一天，外科医生们正在对一名43岁的女性进行子宫切除术。患者在麻醉下失去了意识，所有的一切似乎都按部就班有条不紊——直到她身上的麻醉突然失效了一段时间，她无法睁开眼睛，无法动一动手指。她试图呼吸，可即使是这样最基本的反射也不能正常进行；一根管子卡在她的喉咙里。她的神智清醒着，知道自己正在手术台上，只是一动也不能动，不能向任何人诉说发生了多么可怕的事情。

Studies of anesthesia awareness are full of such horror stories, because administering anesthesia is a tightrope walk. Too much can kill. But too little can leave a patient aware of the procedure and unable to communicate that awareness. For every 1,000 people who undergo general anesthesia, there will be one or two who are not as unconscious as they seem — people who remember their doctors talking, and who are aware of the surgeon's knife, even while their bodies remain catatonic and passive. For the unlucky 0.13 percent for whom anesthesia goes awry, there's not really a good preventive. That's because successful anesthetization requires complete unconsciousness, and consciousness isn't something we can measure.
在关于麻醉觉醒(anesthesia awareness)的研究里，充满了此类恐怖故事，这是由于给予麻醉的确是一项令麻醉医师如履薄冰的棘手任务。用药过量可以致人于死地。但药量不足却可能使患者在手术中醒来，而无法向其他人诉说自己的困境。每1000名接受全身麻醉的患者中，平均会有一或两人(0.13%)不幸并非如表面所见的那样不省人事——他们记得医生们的交谈，感觉得到外科医生的刀划过血肉，尽管此时他们的身体仍然毫无知觉，被动地任人摆弄。目前还没有什么真正有效的方法可以防止麻醉过程中出现这种岔子。因为，成功的麻醉需要实现完全无意识，而我们现有的技术还无法对意识加以衡量。

There are tools that anesthesiologists use to get a pretty good idea of how well their drugs are working, but these systems are imperfect. For most patients receiving inhaled anesthesia, they're no better at spotting awareness than dosing metrics developed half a century ago, says George Mashour, a professor of anesthesiology at the University of Michigan Medical School. There are two intertwined mysteries at work, Mashour told me: First, we don't totally understand how anesthetics work, at least not on a neurological basis. Second, we really don't understand consciousness — how the brain creates it, or even what, exactly, it is.
现在已经有一些工具可以帮助麻醉医师较好地把握自己所用药物的效力，但这些系统还不够完善。密歇根大学医学院(University of Michigan Medical School)的麻醉学教授乔治·马舒尔(George Mashour)表示，对于大多数接受吸入麻醉的患者而言，尚无比半个世纪前研发的用药剂量指标效果更好的知觉观察方法。马舒尔还告诉我，在麻醉工作中存在着两个相互交织的未解谜团：首先，我们并不完全了解麻醉的工作机制，至少在神经学基础的层面上是如此。其次，我们对意识也没有实现真正的理解——大脑如何创造了意识，以及，“意识”的确切定义究竟是什么。

Lacking a way to measure consciousness directly, anesthesiologists monitor for proxies of it — the presence of certain types of brain waves, physical responses and sensitivity to pain — and adjust the dosage if they arise. To improve on this method, neuroscientists are searching for what they call neural correlates of consciousness — changes in brain function as a person transitions from being apparently conscious to apparently unconscious. The more they know about these, the better they hope to understand what consciousness is.
由于无法直接对意识加以测量，麻醉师们只好退而求其次，监测意识的替代物——特定类型的脑电波、生理反应和疼痛敏感度的存在情况，并在上述指标升高时增加麻醉剂量。此外，为了改善这一方法，神经科学家正试图寻找“意识的神经机制”(neural correlates of consciousness)，即，人在从明显的意识知觉状态转变为明显无意识状态的过程中脑功能的改变。他们认为，对此了解得越深入，就越有希望解开意识之谜。

Michael Alkire, associate professor of anesthesiology at the University of California, Irvine, was one of the first people involved in the search for neural correlates of consciousness, back in the 1990s. He's particularly excited now about a study published in August by an international team of researchers based at the University of S?o Paulo and the University of Wisconsin, Madison. They compared the brain activity of patients from the full spectrum of consciousness — awake, asleep, drugged with anesthetics, in comas or suffering from "locked-in syndrome," in which the body appears trapped in a comalike state but the brain is active and aware. The researchers stimulated these subjects' brains with a magnetic field and used EEG to trace the pulse's path. The brains we might think of as conscious and those we think of as unconscious reacted to the stimulus in distinct ways. "If the patient is awake, the electrical ‘ping' can travel all around the brain," Alkire said. "But if they're unconscious, the ‘ping'tends to stay localized and just fades away like a sonar blip."
关于意识的神经机制的研究兴起于20世纪90年代。美国加州大学欧文分校(University of California, Irvine)的麻醉学副教授迈克尔·阿尔基尔(Michael Alkire)是最早参与此类研究的科学家之一。八月份由圣保罗大学(University of S?o Paulo)和威斯康星大学麦迪逊分校(University of Wisconsin, Madison)的研究人员组成的国际研究团队发表了一项研究，令他格外兴奋。该研究比较了患者在整个意识谱系——醒觉、睡眠、接受麻醉剂后、昏迷或罹患“闭锁综合征”（此时，患者的躯体陷入类似昏迷的状态，但大脑仍在活动且醒觉）——的多种状态下大脑活动的异同。研究人员采用磁场来刺激受试者们的大脑，并使用脑电图(EEG)跟踪了脑电脉冲的路径。结果显示，在我们通常认定为有意识或无意识的大脑中，这些刺激引起的反应方式截然不同。“如果患者处于醒觉状态，电脉冲信号可以传遍整个大脑，”阿尔基尔说。“但是，如果他们失去了意识，脉冲信号往往只在局部短暂停留，然后便如昙花一现般消失无踪。”

This finding excites Alkire because it bolsters an existing theory of how consciousness works. Mashour, who also studies neural correlates of consciousness, has repeatedly found evidence that — contrary to conventional- wisdom — sensory networks in the brains of unconscious people remain locally functional, but intrabrain communication has broken down. The neighborhood's lights are on, in other words, but the Internet and phone lines have all been cut.
这些研究结果令阿尔基尔十分振奋，因为它很好地支持了一个现有的意识运作理论。在马舒尔对意识的神经机制进行研究的过程中，与传统观点相背离的证据一再出现，这些证据表明，在无意识者的大脑中，感觉网络仍在局部地发挥作用，只是大脑内部的通信系统完全崩坏了。换句话说，邻近街区的灯照常亮着，可互联网和电话线都被切断了。

The S?o Paulo-Madison study could be showing that unconsciousness is what happens when different parts of the brain can't connect: The signal simply dies. This also suggests that anesthetics work best when they cut those lines of communication. What's more, it provides insight into a vexing question: How can the entirety of human experience arise from tiny electrical impulses?
这项圣保罗-麦迪逊研究显示，无意识是大脑的不同部位间失去联系的外在表现：只是信号无法传递而已。它还表明，当麻醉剂恰好切断那些通信线路时，麻醉效果最好。更重要的是，该研究为我们探讨一个深奥的问题提供了启示：人类的体验作为一个整体，是如何从微小的电脉冲中诞生的？

Neuroscientists do know that consciousness does not reside in any one part of the brain — there is no region where all information is aggregated together — but they don't know much more than that. Consciousness is difficult to study by its very nature, so it has been left mostly to philosophers for the last hundred years — and they don't agree on much. For instance, the philosopher John Searle describes consciousness as a purely subjective experience — what you have when you wake up in the morning, and what disappears when you fall asleep at night (or die, depending on how bad your day was). The philosopher Daniel Dennett wrote a book called "Consciousness Explained," which plays down the subjective experience of consciousness so much that critics dubbed it "consciousness explained away."
神经科学家已然确知，意识并不存在于大脑的任何一个特定部位——并没有一个脑区专司汇总所有的信息——但他们所知的也仅限于此。意识的本质使其难以进行直接研究，因此，在过去的一百年中这一领域的绝大部分都是哲学家们的舞台，可惜他们各执己见，没有达成多少一致意见。例如，哲学家约翰·塞尔(John Searle)将意识描述成了一种纯粹的主观体验——当你在早晨醒来时，你就获得了意识；等你在夜间入睡（或者死亡，这取决于你这一天过得怎么样）时它便消失了。而在哲学家丹尼尔·丹尼特(Daniel Dennett)撰写的名为《意识的解释》(Consciousness Explained)论着中，则大大贬低了意识的主观体验，以至有评论家戏称这本书“把意识给解释没了”。

Scientists largely ignored these sorts of debates for most of the 20th century. But in 1994, an interdisciplinary conference at the University of Arizona brought them together for the first time. That conference led to ongoing research studying the links between anesthesia and consciousness. Stuart Hameroff, an anesthesiologist and the director of the school's Center for Consciousness Studies, was an organizer of the conference. Anesthesia, he told me, is a great example of why scientists have to think about consciousness. It's not enough, he said, just to assume your patient is unconscious because she doesn't respond to pain.
在20世纪的绝大部分时间里，科学家们在很大程度上一直对这些争论视若无睹。但是，1994年美国亚利桑那大学(University of Arizona)举行的一场跨学科会议第一次将科学家和哲学家们聚在了一起。这次会议引发人们就麻醉和意识之间的联系展开了持续的研究。该校意识研究中心(Center for Consciousness Studies)的主任斯图尔特·哈姆鲁夫(Stuart Hameroff)是这次会议的组织者。他告诉我，麻醉是可解释科学家们为何需要思考意识问题的绝佳例子。他说，单凭患者无法对疼痛作出反应并不足以判定他已经失去了意识。