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Having an out-of-body experience? Blame this sausage-shaped piece of your brain
Dr. Josef Parvizi remembers meeting a man with epilepsy whose seizures were causing some very unusual symptoms.
"He came to my clinic and said, 'My sense of self is changing,'" says Parvizi, a professor of neurology at Stanford University.
The man told Parvizi that he felt "like an observer to conversations that are happening in my mind" and that "I just feel like I'm floating in space."
Parvizi and a team of researchers would eventually trace the man's symptoms to a "sausage-looking piece of brain" called the anterior precuneus.
This area, nestled between the brain's two hemispheres, appears critical to a person's sense of inhabiting their own body, or bodily self, the team recently reported in the journal Neuron.
The finding could help researchers develop forms of anesthesia that use electrical stimulation instead of drugs. It could also help explain the antidepressant effects of mind-altering drugs like ketamine.
Finding the seat of the physical self
It took Parvizi's team years of research to discover the importance of this obscure bit of brain tissue.
In 2019, when the man first came to Stanford's Comprehensive Epilepsy Program, Parvizi thought his symptoms were caused by seizures in the posteromedial cortex, an area toward the back of the brain.
This area includes a brain network involved in the narrative self, a sort of internal autobiography that helps us define who we are. Parvizi's team figured that the same network must be responsible for the bodily self too.
"Everybody thought, 'Well, maybe all kinds of selves are being decoded by the same system,'" he says.
A series of experiments on the initial patient and eight other volunteers pointed toward a different explanation.
All the patients had severe epilepsy and were in the hospital as part of an effort to locate the source of their seizures. The process requires placing electrodes in the brain and then waiting for a seizure to occur.
These electrodes can also be used to deliver pulses of electricity. So Parvizi's team was able to stimulate different areas of the brain to see whether they affected a person's sense of self.
When the team stimulated the anterior precuneus, "lo and behold, everybody has changes in their sense of what we call the bodily or physical self," Parvizi says.
In other words, the stimulation produced an out-of-body experience. People felt detached from their own thoughts and no longer anchored in their own bodies.
The finding was surprising because the anterior precuneus is separate from the brain's system for maintaining a narrative self. Instead, it appears devoted to the sense that something is "happening to me," not another person, Parvizi says.
"We think this could be a way for the brain to tag every experience in the environment as 'mine,'" he says.
A shift in perspective
That role for the anterior precuneus makes sense, says Christophe Lopez, a researcher at the National Centre for Scientific Research in France.
Lopez has done research suggesting that our sense of a physical self comes in part from the inner ear, which detects motion and monitors the body's position in space. And the results from Parvizi's team suggest that signals from the inner ear are processed by the anterior precuneus.
"When they stimulate the anterior precuneus, you can evoke that the body is floating or the body is falling," Lopez says.
That means the brain has to make sense of conflicting information: For example, signals from the inner ear may say the body is falling while signals from the eyes say it's stationary.
As a result, Lopez says, the brain may try to cope by taking a different perspective.
"Sometimes the best solution which is found by the brain is to think that you are somewhere else, out of the body," he says.
The brain may face a similar conundrum when people take drugs like ketamine, which affect the anterior precuneus.
"Ketamine seemingly is producing this artificial rhythm [in the brain] that is disrupting function of that area," says Patrick Purdon, an associate professor of anesthesia at Harvard Medical School.
That slow rhythm is similar to the one that Parvizi's team saw when it stimulated the brains of epilepsy patients, Purdon says.
That could mean it will someday be possible to use electrical pulses in place of anesthetic drugs like ketamine, he says.
"You could get the specific brain areas that you want without having to cause a brainwide and systemwide effect that might carry with it a lot of side effects," Purdon says.
注释：
epilepsy: n
表示" 癫痫症; 羊角风"，means "a disorder of the central nervous system characterized by loss of consciousness and convulsions"，如：his simple method might provide a valuable hint for the treatment of epilepsy. 这方法或许对癫痫症的处置可以提供有价值引导。
seizure: n
表示"发作; 没收"，means "a sudden occurrence (or recurrence) of a disease; the act of forcibly dispossessing an owner of property"，如：He was released the day after suffering a seizure.心脏病发作的第二天，他就出院了。The courts ordered the seizure of all her property. 法院下令查封她所有的财产。We know the importance of the seizure of power by armed force. 我们知道武装夺取政权的重要性。
precuneus: n
表示"楔前叶"，如：But neither the precuneus nor the vMPFC showed any change in the group who watched the computer. 然而观察电脑的那组学生的大脑楔前叶和大脑腹内侧前额皮质区域都没有出任何异动的迹象。
anesthesia: n
表示" 麻醉；麻木"，means "loss of bodily sensation with or without loss of consciousness"，如：Anesthesia was a great innovation in medicine. 麻醉是一项伟大的医学创新。
antidepressant: n
表示" 抗抑郁剂"，means "any of a class of drugs used to treat depression; often have undesirable side effects"，如：Doctors might suggest anti-anxiety or antidepressant medicines. 医生可能建议吃抗焦虑后者抗抑郁剂。
ketamine: n
表示" 克他命；凯特明(一种高效麻醉剂)"，如：Ketamine is not approved for depression, and it has a checkered past in psychiatric research. 克他命没有获得允许用于治疗抑郁症，在精神病研究方面过去一直充满变数。
posteromedial: adj
表示"[医] 后中的"，means ""，如：posteromedial central arteries 后内侧中央动脉
cortex: n
表示" 外皮；（大脑）皮层"，如：The mantle of graymatter forming the cerebral cortex. 大脑皮层形成大脑皮层智力的外表
autobiography: n
表示" 自传"，means " the story of a person's life, written by that person; this type of writing"，如：He rounded out his quartet with an autobiography. 他以自传作为他的四部曲的结尾。
electrode: n
表示" 电极；电焊条"，means "a conductor used to make electrical contact with some part of a circuit"，如：The positive electrode is a rod of hard carbon fitted with a brass cap. 正电极是一个装有黄铜帽的硬碳棒。
conundrum: n
表示" 谜语；难题"，means "a difficult problem"，如：I'm going to tell you why this conundrum exists. 我打算告诉你们为什么这个谜题存在。
中文简要说明：
神经学教授帕尔维兹（Josef Parvizi）在史丹佛大学回忆起一位患有癫痫的病人，他的癫痫发作导致了一些非常不寻常的症状，问诊时病人谈到自己会变成旁观者的角度听着、看着自己大脑里的思绪，还会感觉到自己飘浮起来或一路飞到天上的感觉，也就是很典型的灵魂出窍或者出体经验。经帕尔维兹和他的团队研究后他们认为这跟病患大脑楔前叶（Precuneus）有关，相关研究目前已经在国际医学期刊《神经元》（Neuron）上公开。
据美国《全国公共广播电台》（NPR）报导，帕尔维兹和一个研究团队最终将这位病人的症状追溯到了一个被称为楔前叶的脑部区域，该团队最近在《Neuron》期刊中报告称，这个位于大脑左半叶和右半叶之间的区域对于一个人，和自己身体的感知，以及自我存在感非常重要，这个区域包括一个参与叙事、自我的脑网络，这种内在的自传帮助我们定义自己的身份。
他说：「大家都认为，也许各种自我都是由同一个系统译码的。」这个发现可能有助于研究人员开发使用电刺激而非药物的麻醉形式。它还可能有助于解释类似氯胺酮／K他命（ketamine）等会改变心智的药物的抗忧郁作用。
帕尔维兹的团队花了多年的研究时间才发现这个脑部区域的重要性。2019年，当这位病人首次来到史丹佛大学的综合性癫痫计划时，帕尔维兹认为他的症状是由大脑后中央皮质的癫痫发作引起的，这是大脑后部的一个区域，位置也差不多就在楔前叶。
至于为什么会有灵魂出窍的感觉，法国国家科学研究中心的研究员洛佩兹（Christophe Lopez）表示，前楔前叶扮演这样的角色很有道理。洛佩兹的研究表明，我们对身体自我的感知部分来自内耳，内耳可以检测运动并监测身体在空间中的位置。帕尔维兹团队的结果表明，内耳送进来的神经讯号，正是由楔前叶所处理的。」
洛佩兹说：「当他们刺激楔前叶时，你会产生身体漂浮或身体下坠的感觉。」这意味着大脑必须理解矛盾的神经信息：例如，来自内耳的信号可能说身体正在下坠，而来自眼睛的信号则说身体是静止的。
因此，洛佩兹表示，大脑可能会尝试从不同的角度应对这些矛盾的神经信号。有时候，大脑找到的最佳解决方案是让你认为自己身在别处，离开了自己的身体。」
因此当人们使用会影响楔前叶的K他命或其他药物时，大脑可能也会陷入类似的矛盾困境，或许不远的未来就可以使用适当电击楔前叶的治疗方式，来取代一些有副作用的药品，从而治疗忧郁症。
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