How near-death experiences arise in the brain

大脑是如何产生濒死体验的

Researchers put forward a comprehensive model outlining the conditions that may give rise to the vivid mental phenomena that some people experience as they near death

研究人员提出了一套综合模型，试图解释为何人在濒临死亡时会产生如此生动的精神现象

Everyone dies, but what actually transpires during that process is a deep mystery that scientists are only beginning to seriously investigate.

死亡是所有人的归宿，但在死亡的过程中究竟发生了什么，仍然是一个深奥的谜题，科学家们才刚刚开始认真探索。

Increasingly, near-death experiences, or NDEs, are part of that growing field.

而濒死体验（NDEs）正逐渐成为这一新兴研究领域的重要课题。

An incredible 5 to 10 percent of the general population reports memories of an NDE.

令人惊讶的是，约5%至10%的人声称自己拥有濒死体验的记忆。

Oftentimes, people’s recollections are similar: perceiving separation from the body and viewing it from above, passing through a tunnel and seeing a light, encountering deceased loved ones or compassionate entities and being overcome by ineffable wisdom and a feeling of profound peacefulness.

这些回忆往往高度相似：感到灵魂脱离躯壳，升到上空俯瞰自己的身体，然后穿过一条隧道看到一束光芒，遇见已故的亲人或某种慈悲的存在（译者注：compassionate entities 通常指的是一些超自然的或灵性上的存在，可能是神灵、天使、守护灵或其他具备慈悲、同情的人物或力量），同时被难以言喻的智慧与深沉的平静感包围。

Many people describe these memories in crisp detail and say that they felt “more real than real.”

许多人能以极为清晰的细节描述出这些记忆，并称其感受“比现实还要真实”。

How a person’s faltering consciousness produces such fantastical experiences is unknown.

人类（濒临死亡）意识逐渐衰退时为何能产生如此奇幻的体验？这至今仍是未解之谜。

But scientists have been piecing together hypotheses, constructed from interviews with survivors, studies in animals and experiments in which people were given certain psychedelic drugs.

不过，科学家们正通过访谈濒死体验的幸存者、开展动物实验，以及进行致幻药物的人体试验，逐步拼凑出各种假说。（译者注：psychedelic drugs 是一类能够显著改变感知、思维、情绪和意识状态的化学物质，这些药物通常能引起视觉、听觉以及其他感官的幻觉。）

Now one of the preeminent research groups investigating NDEs has published what it describes as the first comprehensive neuroscientific model for the phenomena.

如今，一个顶尖的濒死体验研究团队发表了他们所谓的首个综合性神经科学模型，以解释这一现象。

“We found a very robust explanation for the generation of such a rich experience while a person is really in crisis,” says Charlotte Martial, a neuroscientist at the University of Liège in Belgium and co-lead author of the findings, published this week in Nature Reviews Neurology.

比利时列日大学的神经科学家夏洛特·马夏尔（Charlotte Martial）表示：“我们已经找到了一个强有力的解释，说明为何人在生命危急时会产生如此丰富的体验。”她是这项研究的首席作者之一，该研究成果已于本周发表于《自然·神经病学评论》期刊。

Martial and her colleagues’ model lays out a step-by-step hypothesis for the conditions that give rise to NDEs. They also propose an evolutionary theory for why these experiences occur.

马夏尔和同事提出的模型逐步阐述了濒死体验产生的条件假说，同时还从进化角度解释为何会产生濒死体验。

To create the model, the authors undertook an exhaustive review of all the studies they could find on NDEs, which ranged from neuroscientific investigations to spiritual perspectives.

为了构建这一理论模型，研究团队系统梳理了所有有关濒死体验的研究文献——从神经科学实验到灵性研究，不一而足。（译者注：spiritual perspectives 指的是从宗教、灵性或超自然的角度来解释濒死体验。）

They also included research on ecstatic seizures, psychedelics and the dying brain.

研究还包含了狂喜型癫痫症、致幻剂实验以及濒死状态下的脑活动分析。（译者注：ecstatic seizures 指的是一种癫痫发作类型，患者在发作时经历极端的愉悦或狂喜的情绪。）

Additional clues came from studies that showed that individuals who have certain predispositions are more likely to experience NDEs. This includes prolific daydreamers, as well as those with a propensity for rapid eye movement (REM) sleep intrusion, which occurs when REM sleep bleeds into wakefulness or non-REM sleep.

此外，他们还参考了一些研究，这些研究表明某些群体更有可能经历濒死体验：一是爱做白日梦的人；二是有快速眼动（REM）睡眠入侵倾向的人——也就是说，在清醒状态或非 REM 睡眠阶段，却体验了 REM 睡眠阶段才有的现象。（译者注：daydreaming 是指人在清醒的时候，思想游离于现实，让自己沉浸在各种想象中；REM sleep 是睡眠的一个阶段，特点是大脑活动非常活跃，眼睛会快速移动，并且通常伴随着做梦。）

NDEs themselves are triggered by a precipitating event, such as a cardiac arrest, that causes a cascade of physiological stress.

濒死体验往往由心脏骤停等突发性事件触发，这会引发一连串的生理应激反应。

The authors propose that certain networks of neurons go into overdrive to produce high levels of specific neurotransmitters in the drastically altered brain environment.

研究者认为，在剧烈变化的大脑环境中，特定神经元网络会过度活跃，从而产生大量神经递质。

The researchers investigated several of those systems and hypothesized ways that they may contribute to distinct mental experiences as the person approaches death.

通过对多个神经系统的研究，研究人员提出了这些物质如何促成濒临死亡时的独特精神体验。

The fact that people can clearly remember NDEs, the authors write, is likely because of the activity of three main neurotransmitters: acetylcholine, which is involved in memory, learning and attention; noradrenaline, which plays a key role in the fight-or-flight response, as well as attention, focus and memory; and glutamate, another learning and memory aid that is also responsible for orchestrating overall brain function by instructing neurons to communicate with one another.

研究指出，人们之所以能够清晰地记住濒死体验很可能与三种主要神经递质活动有关：一是乙酰胆碱（acetylcholine），它与记忆、学习和注意力相关；二是去甲肾上腺素（noradrenaline），它在“战斗或逃跑”反应中起到关键作用，同时也与注意力、专注力和记忆相关（译者注：fight-or-flight response 是指当人们面临威胁或危险时，身体为应对这些威胁而做出的生理反应，要么准备“战斗”对抗威胁，要么准备“逃跑”避开危险）；三是谷氨酸（glutamate），这是另一种帮助学习和记忆的神经递质，同时还负责通过调控神经元间的信息传递来协调整体脑功能。

Beyond the triad of chemical culprits, the researchers linked the calm, peaceful feeling that characterizes many NDEs with activation of 5-HT1A receptors by serotonin, as well as with transient rises in endorphins—the body’s natural pain relievers and mood enhancers—and GABA, a neurotransmitter that reduces neurons’ activity.

除上述三种关键的神经递质外，研究人员还发现，濒死体验中特有的平静祥和感，与血清素激活 5-HT1A 受体密切相关（译者注：serotonin 是一种神经递质，参与调节情绪、睡眠、焦虑、平静感等；5-HT1A 是一种大脑里的神经递质受体，是血清素受体家族中的一个亚型），同时也源于内啡肽（人体天然的止痛剂和情绪提升剂）和GABA（一种减少神经元活动的神经递质）的短暂升高。

For the vivid hallucinations that oftentimes accompany NDEs, the team pointed to serotonin’s hyperactivation of 5-HT2A receptors.

对于濒死体验中常见的生动幻觉，研究团队将其归因于血清素对 5-HT2A 受体的过度激活。

Dopamine likewise contributes to the altered visual experience and lends a sense of realism.

此外，多巴胺不仅有助于改变视觉体验，更赋予这些幻觉一种真实感。（译者注：dopamine 在调节大脑中的奖赏系统、愉悦感、情绪、注意力、学习和运动控制等方面发挥着重要作用。）

The new model calls into question a prior hypothesis that a yet-undiscovered, naturally occurring chemical in the brain plays a role in inducing NDEs by blocking the same receptors that the synthetic drug ketamine binds to. ***

这项新模型对先前的一个假说提出了质疑——该假说认为大脑中有某种尚未被发现的天然化学物质，通过阻断合成药物氯胺酮（ketamine）所结合的那些受体，从而诱发濒死体验。

Those receptors, however, are essential for memory formation, so if they were blocked, people should not be able to recall NDEs with such clarity, says Nicolas Lejeune, senior author of the new study and a neurorehabilitation clinician and researcher at the University Hospital of Liège. “Instead of assuming the existence of an unknown neurochemical, we propose that NDEs arise from disruptions that naturally occur in response to life-threatening events,” he says.

然而，作为本研究资深作者、列日大学医院神经康复临床研究员尼古拉·勒琼（Nicolas Lejeune）指出：“这些受体对记忆形成至关重要，如果它们被阻断，人们就不可能如此清晰地回忆濒死体验。与其假设存在某种未知的神经化学物质，我们认为濒死体验其实就是生命受到威胁时自然发生的神经活动紊乱所致。”

Finally, the researchers also put forward an idea for why the brain evolved to react this way.

最后，研究者还从进化角度提出了大脑产生这种反应的原因。

The neurochemical model, they argue, dovetails with other research suggesting that NDEs are the human version of “playing dead.”

他们认为，这一神经化学模型与其他研究不谋而合——濒死体验很可能是人类的“假死”反应。

Many species use this last-ditch survival effort in the face of mortal danger after fight or flight fails.

许多物种在面临致命危险时，当“战斗或逃跑”反应失败后，会启动这种终极生存策略。

In feigning death, the animal goes limp and becomes unresponsive to external stimuli. But it remains aware of its surroundings, so if given the chance, it can escape.

动物假死时会全身瘫软，对外界刺激毫无反应，但仍保持环境感知能力，以便伺机逃脱。

The idea that “playing dead” could be the evolutionary origin of near-death experiences is backed up by the fact that some people who perceived themselves to be in life-threatening circumstances but were not actually physically harmed have reported near death-like experiences. ***

支持这一进化起源假说的事实证据是：某些并未真正受伤但自认为身处险境的人，也曾表示经历过类似濒死的体验。

The otherworldly, shared components of these experiences may be the human brain’s attempt to make meaning out of what’s happening.

这些体验中共有的超现实元素，可能是人类大脑试图为发生的事情赋予意义。

“In a sense,” Martial says, “NDEs are a passive coping mechanism to enhance survival in life-threatening circumstances.”

马夏尔指出：“从某种意义上说，濒死体验是一种被动应对机制，有助于在生命受到威胁的情况下提高生存能力。”

Martial and her colleagues acknowledge that their new model is only a first step toward creating a more robust framework—one that, ideally, will be supported by physiological data.

马夏尔和她的同事承认，这一新模型只是为建立一个更为严谨的理论框架所做出的初步尝试，理想情况下，该框架应获得生理学数据的支持。

The hypotheses they lay out for various features of NDEs could be road maps, Martial says, “for future empirical studies that will aim to go into more details.”

马夏尔表示，他们针对濒死体验各个特征提出的假说，可以成为未来实证研究的蓝图，“以便未来更详细地探索这些现象。”

By investigating the extreme end of human experience, she adds, these future studies could also help to shed light on the mechanisms of consciousness itself.

她还补充道，通过对人类极端体验的探索，未来的研究或许有助于揭示人类意识本身的运作机制。