实时影像：初窥麻醉中的大脑
作者：迈亚.萨拉维兹（Maia Szalavitz ）发表于2011.6.15周三译者：Ifurzzar译于：2011.7.6 What happens to your brain as it slips into unconsciousness? A new technique allows researchers to view real-time 3-D images of a patient undergoing anesthesia using the drug propofol, and the findings show that consciousness isn't suddenly switched off, but rather fades as though a dimmer is being dialed down.当你的大脑渐渐丧失意识时，它到底发生了什么？得益于一项全新的技术，研究人员观察到了一位被异丙酚麻醉的患者大脑的实时3D图像。而观察得到的结果告诉我们意识并不会突然丧失。就好像慢慢拨向0刻度的调光器一般，意识也是逐渐减弱并消失的。The research also suggests that consciousness resides in the connections between multiple parts of the brain, not in any single region. The images show that changes in the anesthetized brain start in the midbrain, where certain receptors for a neurotransmitter called GABA are plentiful.这项研究同样表明，意识并不处于任何单独的大脑区域，它的存在依赖于大脑多个部分间的联系。视频图像显示被麻醉的大脑从中脑部分开始发生变化。中脑中大量存在着某类神经末梢，这类神经末梢能接收名为GABA（伽马氨基丁酸）的神经递质。Drugs like propofol act on these GABA A receptors, mimicking and enhancing the effects of GABA, which inhibits cellular activity. From the midbrain, changes move outward to affect the whole brain; as propofol's message spreads from region to region, consciousness dissolves.异丙酚一类的药物能够作用于这类接收GABA的神经末梢，通过模拟和增强GABA引起的效果，起到抑制细胞活性的作用。最初出现于中脑的变化会向外扩展，并最终影响到整个大脑；随着异丙酚诱发的神经信息从一处脑部区域传递到另外一处，意识也随之消逝。"Our jaws ricocheted off the ground, and I won't say the words we used when we first saw the video," says lead author Dr. Brian Pollard, professor of anesthesia at the University of Manchester, who presented the results at the European Anesthesiology Conference in Amsterdam on Saturday. "We just sat there and stared, dumbfounded and kept repeating it. We're the first people in the world ever to see the brain becoming unconscious, that's quite a sobering thought."“我们岂止是吃惊得下巴落地，它甚至还弹了起来！我都没法把我们第一次看到视频影像时的胡言乱语对你再说一遍，”作为主要作者的布莱恩.伯拉德博士（Dr. Brian Pollard）如是告诉我们。布莱恩.伯拉德博士是曼彻斯特大学（University of Manchester）的麻醉学教授，他已经于这周六向欧洲麻醉学联合会（European Anesthesiology Conference）呈递了研究结果。“我们坐在那儿紧盯着屏幕，目瞪口呆地看了一遍又一遍。我们是世界上首批亲眼目睹了大脑是如何失去意识的人，这一点光是想想就让人觉得不能等闲视之。”Although anesthesia has been widely used since 1846, when a dentist first demonstrated the effects of ether at Massachusetts General Hospital, until recently very little has been understood about how it works. Even though scientists know that anesthetic drugs like propofol affect GABA in the brain, how that actually eliminates consciousness still remains a mystery.1846年，一位牙医在马萨诸塞州综合病院（Massachusetts General Hospital）首次展示了乙醚的麻醉效果，从此之后麻醉剂就开始被广泛使用。然而直到最近我们对麻醉剂生效的方式仍然知之甚少。虽然科学家知道像是异丙酚之类的麻醉药能影响脑内的GABA，但是这种影响在实质上是如何使意识丧失的却还是一个未解之谜。Pollard explains, however, that propofol alters "the balance between inhibition and excitation in the brain," shifting the balance of activity toward the inhibitory circuits. At first, this produces a paradoxical result.然而，伯拉德解释说异丙酚打破了“脑内抑制作用和兴奋作用间的平衡，”它将天平从脑内活跃回路的一端拨向了抑制回路（inhibitory circuits）的一端。在一开始，这一转变会产生一个自相矛盾的结果。"When inhibition is inhibited, you first move into a stage of excitation or mania," he says, noting that this usually occurs too quickly to be observed with modern anesthesia. But the brief sense of euphoria that some people experience before losing consciousness from propofol may reflect this loss of inhibition (and may also account for Michael Jackson's taste for the drug).“当抑制作用受到抑制时，你首先会进入一种兴奋或者狂躁的状态，”他说，并且还提及到在使用现代麻醉技术时，这一现象会发生得非常迅速以至于观察不到。但是某些使用异丙酚的人在丧失意识前会体验到到短暂的欢欣感，这种现象也许正是反映了这种抑制作用的丧失（同时这也许能解释为什么迈克尔·杰克逊（Michael Jackson）对这种药物情有独钟）"You then begin to inhibit the excitation and the patient becomes more sedated and loses consciousness," he says. That's why in the video the brain appears to become more active while unconscious: it's showing the increased action in inhibitory circuits.“患者的大脑随后会开始抑制兴奋作用，而他会变得镇定，而后丧失意识，”他说。这就是为什么视频影像中的大脑在无意识状态下看起来变得更加活跃：这一现象显示出抑制回路的活动得到了增强。"What we've got supports the idea that there are several levels rather than switch," he says.
“我们所得到的信息证实了这样一种观点：所谓‘意识’具有不同的阶段，而非仅仅在‘开启/关闭’间转换，”他说。点击此处观看原文以及视频影象Pollard's group used a new technology called fEITER, for functional electrical impedance tomography by evoked response. To measure brain activity, the technique uses imperceptible electrical currents produced by electrodes placed on the head. Unlike fMRI, it doesn't require the patient to be placed inside a magnetic field, which precludes the use of metal devices, so the laptop-size fEITER instrument could be used in an ordinary operating room.伯拉德的团队使用了一项名为“飞特”（fEITER）的全新技术，所谓fEITER既是“诱发响应式功能性电抗组X射线成像术”（functional electrical impedance tomography by evoked response）的缩写。这种技术使用置于头部的电极来产生极微小的电流，并通过电流来测量大脑活性。与磁共振技术（fMRI）不同，这种技术并不需要将患者置于磁场内——而磁场的存在则意味着不能使用任何金属器械。因此和笔记本电脑一般大小的“飞特仪”在普通手术室就可以使用。"We can get lot of mileage to separate out anesthesia, sedation and consciousness," says Pollard. The device could also potentially be used to rapidly determine the site of a stroke or the extent of a brain injury.“它（研究中的‘飞特’技术）让我们的工作向前迈进了一大步，从而使我们可以清楚地划分出‘麻醉状态’、‘镇定状态’和‘清醒状态’，”伯拉德说道。这种仪器甚至有潜力被运用于快速诊断中风位置和脑部损伤的程度。 "This is a great idea and I think it's very exciting," says Dr. Emery Brown, professor of computational neuroscience at MIT, but he cautions that since the research has not yet been published in a peer-reviewed journal, the results must be seen as preliminary. Still, he says that the research may offer "new insight into how anesthesia works."“这个点子太棒了，而且我觉得它非常令人兴奋，”埃默里.布朗博士（Dr. Emery Brown）说，他是麻省理工学院计算神经学的教授。但布朗博士同时还告诫道，由于这项研究还未在由同业者校审的期刊上发表过，因此研究成果还处于初期阶段。尽管如此，他仍旧评价说这项研究也许能“为我们认识麻醉剂起效的方式提供全新的视角。”Ultimately, fEITER might be used to make sure that patients do not experience any consciousness during surgery. About 1 in 1,000 to 2,000 patients experiences some degree of consciousness under anesthesia, which can obviously be extremely traumatic. However, it's difficult for doctors to determine when consciousness is occurring, because drugs used in surgery also paralyze the body and affect measures of stress like blood pressure. A better understanding of what consciousness is could help eliminate this possibility.最后，“飞特”技术还可能被用于确保患者在手术中不会回复意识。在1000到2000名患者中会有一人在麻醉状态下回复一定程度的意识，这种情形毫无疑问会对手术中的当事人造成极大的心理创伤。然而，因为手术中使用的麻醉剂同样会麻痹患者的身体，从而扰乱衡量体内压强的计量标准，例如血压，所以医生很难确定病患会在何时回复意识。更好地理解“意识”究竟为何物将帮助我们消除患者在手术中苏醒的可能性。 While Pollard is optimistic about using imaging of anesthesia to understand consciousness itself, Brown is more skeptical. He notes that it's much easier to break something than it is to build it. In other words, knowing what's being disconnected during unconsciousness might not illuminate much about what's happening during consciousness. Either way, a better understanding of the circuits involved in unconsciousness has a lot to offer medicine.尽管伯拉德乐观地认为使用这项麻醉成像技术可以使我们更深入地理解何谓“意识”，布朗却抱持怀疑态度。他提醒我们说破坏一个事物要比建造它容易许多。换句话说，知道了在无意识状态下大脑中有哪些东西会“断离”开，也许并不能解答在清醒的大脑中发生了什么。但无论怎样，能够更好地理解无意识状态涉及的脑内回路，这一点对医学来说将大有助益。 Real-Time Video: First Look at a Brain Losing Consciousness Under Anesthesia
What happens to your brain as it slips into unconsciousness? A new technique allows researchers to view real-time 3-D images of a patient undergoing anesthesia using the drug propofol, and the findings show that consciousness isn't suddenly switched off, but rather fades as though a dimmer is being dialed down.
The research also suggests that consciousness resides in the connections between multiple parts of the brain, not in any single region. The images show that changes in the anesthetized brain start in the midbrain, where certain receptors for a neurotransmitter called GABA are plentiful.
Drugs like propofol act on these GABA A receptors, mimicking and enhancing the effects of GABA, which inhibits cellular activity. From the midbrain, changes move outward to affect the whole brain; as propofol's message spreads from region to region, consciousness dissolves.
"Our jaws ricocheted off the ground, and I won't say the words we used when we first saw the video," says lead author Dr. Brian Pollard, professor of anesthesia at the University of Manchester, who presented the results at the European Anesthesiology Conference in Amsterdam on Saturday. "We just sat there and stared, dumbfounded and kept repeating it. We're the first people in the world ever to see the brain becoming unconscious, that's quite a sobering thought."
Although anesthesia has been widely used since 1846, when a dentist first demonstrated the effects of ether at Massachusetts General Hospital, until recently very little has been understood about how it works. Even though scientists know that anesthetic drugs like propofol affect GABA in the brain, how that actually eliminates consciousness still remains a mystery.
Pollard explains, however, that propofol alters "the balance between inhibition and excitation in the brain," shifting the balance of activity toward the inhibitory circuits. At first, this produces a paradoxical result.
"When inhibition is inhibited, you first move into a stage of excitation or mania," he says, noting that this usually occurs too quickly to be observed with modern anesthesia. But the brief sense of euphoria that some people experience before losing consciousness from propofol may reflect this loss of inhibition (and may also account for Michael Jackson's taste for the drug).
"You then begin to inhibit the excitation and the patient becomes more sedated and loses consciousness," he says. That's why in the video the brain appears to become more active while unconscious: it's showing the increased action in inhibitory circuits.
"What we've got supports the idea that there are several levels rather than switch," he says.
Pollard's group used a new technology called fEITER, for functional electrical impedance tomography by evoked response. To measure brain activity, the technique uses imperceptible electrical currents produced by electrodes placed on the head. Unlike fMRI, it doesn't require the patient to be placed inside a magnetic field, which precludes the use of metal devices, so the laptop-size fEITER instrument could be used in an ordinary operating room.
"We can get lot of mileage to separate out anesthesia, sedation and consciousness," says Pollard. The device could also potentially be used to rapidly determine the site of a stroke or the extent of a brain injury.
"This is a great idea and I think it's very exciting," says Dr. Emery Brown, professor of computational neuroscience at MIT, but he cautions that since the research has not yet been published in a peer-reviewed journal, the results must be seen as preliminary. Still, he says that the research may offer "new insight into how anesthesia works."
Ultimately, fEITER might be used to make sure that patients do not experience any consciousness during surgery. About 1 in 1,000 to 2,000 patients experiences some degree of consciousness under anesthesia, which can obviously be extremely traumatic. However, it's difficult for doctors to determine when consciousness is occurring, because drugs used in surgery also paralyze the body and affect measures of stress like blood pressure. A better understanding of what consciousness is could help eliminate this possibility.
While Pollard is optimistic about using imaging of anesthesia to understand consciousness itself, Brown is more skeptical. He notes that it's much easier to break something than it is to build it. In other words, knowing what's being disconnected during unconsciousness might not illuminate much about what's happening during consciousness. Either way, a better understanding of the circuits involved in unconsciousness has a lot to offer medicine.
好消息，如果能实现临床广泛应用，对于探明麻醉机理可能有很大的帮助哟
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