科学小实验 | 实验台厂家



Going under

Tracking the brain’s electrical activity can make anaesthesia safer





AROUND 1936 three neurologists at Harvard Medical School raided the medicine cabinet, filling their boots with morphine, barbiturates, ethers and even cobra venom. They injected those substances into (apparently) willing volunteers and cemented primitive electrodes to their scalps and earlobes. They also collared a drunk and wired him up. With pen and paper, they then recorded how the electrical signals in their volunteers’ brains changed as the drugs began to take hold. 大约在1936年,哈佛医学院的三位神经学家扫荡了药品柜,把大堆的吗啡、巴比妥类和醚类药物,甚至还有眼镜蛇毒,都塞进了汽车后备箱。他们把这些药物注射到(看起来是)心甘情愿的志愿者体内,再把简陋的电极贴到他们的头皮和耳垂上。他们还给一名醉汉带上颈圈接通电源。然后当药物开始起效时,他们用纸笔记录下志愿者脑电信号的变化。

This kind of gonzo science might meet a touch of resistance from the institutional review board if proposed today, but the work of Gibbs, Gibbs and Lennox still stands. The trio showed, without meaning to, that sedatives lower the activity of the brain through several clear stages, and that each stage is observable in that organ’s electrical readings. Their results have been refined over the years, of course, to the extent that Emery Brown, a successor of theirs at Harvard, now thinks, as he told the AAAS meeting, that statistical analysis of such electroencephalography (EEG) signals has become so good that it can be used to make anaesthesia safer and better. 如果是在今天,提议做这样疯狂的科学试验可能会遭到医学院伦理审查委员会的些许阻力,不过,吉布斯(Gibbs)夫妇和伦诺克斯(Lennox )的研究成果至今仍站得住脚。他们无意中证明了镇静剂对大脑活动的抑制分为几个明显的阶段,每个阶段都可以在脑电图中观察到。当然,多年来他们的结论也经过不断改进。现在,他们在哈佛的一位继承者埃默里·布朗(Emery Brown)在美国科学促进会(AAAS)会议上表示,对这种脑电(EEG)信号的统计分析已经做得非常之好,可以利用它们来使麻醉变得更安全有效。

The EEG of a conscious brain shows no striking features, just low-amplitude and seemingly uncorrelated ups and downs in the frequency of oscillations in the brain’s electric field. That is because the brain’s neurons are firing independently of one another as they go about the various tasks that render their owner conscious. Then (as the Harvard trio found) as the patient goes under the oscillations smooth out, deepening into a stark, uniform wave which vibrates ten times a second. The drug has tripped the neurons into singing from the same hymn sheet. Their unified song takes over from the cacophony of a conscious brain, and the patient is out. 当大脑意识清醒时,脑电图没有显著的特征,只能看到脑电场的振荡频率有着幅度很低、看起来互不关联的起伏。这是因为大脑的神经元在相互独立地放电,进行各种活动,从而使人保持清醒。然后(就像哈佛的三位学者发现的那样),当病人开始昏迷时,振荡趋于平滑,加深成为一个明显而均匀的波,每秒振动十次。药物触发了神经元步调一致地放电。它们奏响的单一乐章取代了大脑清醒时的各种杂音,病人陷入昏迷。

That, Dr Brown believes, gives anaesthetists a better way to assess how deeply someone is under than measuring blood pressure and heart rate. He regularly uses brain waves clinically. In a recent operation, for example, he was able to administer a third of the normal dose of an anaesthetic called propofol to an 81-year-old cancer patient, monitoring her brain waves to ensure that she was deeply under at all times. Indeed, he thinks he may be able to automate the whole process, and has designed a machine which adjusts the dose in response to brainwave changes. 布朗认为,这给了麻醉师一种比测量血压和心率更好的方法来判定一个人的昏迷程度。他经常在临床上使用脑电波。例如,在最近一次手术中,他要给一位81岁的癌症病人注射一种名为丙泊酚(propofol)的麻醉剂,他通过监测脑电波来确保她一直处于深度昏迷,结果只用了正常剂量的三分之一。事实上,他认为他或许可以让整个过程都自动化,并已设计了一台能根据脑电波变化来调整剂量的机器。

He also believes that the potential for using EEG to understand unconscious brainwaves goes beyond the operating table. Sleeping pills, for instance, do not so much aid sleep as sedate their recipient. Dr Brown thinks insomniacs might be guided into true sleep through a more precise examination of their brain activity, and the application of commensurate drugs. 他还认为,用脑电图来读懂无意识大脑的脑电波,可应用的范围超出了手术台。例如,安眠药的镇静作用大于助眠作用。布朗认为,通过更精确地检测失眠患者的大脑活动,并使用相应的药物,或许可以将患者导向真正的睡眠。

Moreover, true successor to Gibbs, Gibbs and Lennox that he is, Dr Brown reveals his own gonzo side when he says his understanding of EEG readouts is such that he believes he could safely place someone into, and then retrieve him from, a “locked-in” state—one in which a person is fully aware of his surroundings, but incapable of any movement or action. When your correspondent offered himself as a test subject, only partially in jest, Dr Brown flashed an arch grin, before sombrely explaining that such an experiment would be beyond the tolerance of modern review boards, too. 此外,作为吉布斯夫妇和伦诺克斯的忠实继承人,布朗也显现出了自己疯狂的一面。他说他相信脑电图读数可以达到这样的程度:他能安全地把一个人放进或抽离“闭锁”状态——一个人能充分意识到自己所处的环境,但不能做出任何动作或行动。当本记者半开玩笑地提出自己来当试验对象时,布朗调皮地露齿而笑,接着严肃地解释说,这样的实验也是现代审查委员会不能容忍的。

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