Can you still feel a limb that's gone? - Joshua W. Pate

翻译人员: Yifan L 校对人员: Hanlin Wang

The vast majority of people who’ve lost a limb can still feel it—

大多数失去肢体的人们 仍能感受到它们的存在—

not as a memory or vague shape, but in complete lifelike detail.

其形式并非记忆或者模糊的形状， 而是人能感受到的种种逼真细节。

They can flex their phantom fingers

他们能弯曲幻肢中的手指

and sometimes even feel the chafe of a watchband

有时甚至可以感受到手表表带的摩擦

or the throb of an ingrown toenail.

或者嵌甲的刺痛。

And astonishingly enough,

更惊人的是，

occasionally even people born without a limb can feel a phantom.

有时那些生来就肢体残疾的人 也能感受到这种幻觉。

So what causes phantom limb sensations?

所以是什么造成了 幻肢的感知呢？

The accuracy of these apparitions

这些幻觉感知的精确度

suggests that we have a map of the body in our brains.

暗示着我们的大脑里有一张身体地图。

And the fact that it’s possible

而生来便肢体残疾的人

for someone who’s never had a limb to feel one

有可能感受到幻肢的这个事实，

implies we are born with at least the beginnings of this map.

说明了我们从出生以来 就拥有地图的起点。

But one thing sets the phantoms that appear after amputation

但是在截肢后出现的这种幻肢

apart from their flesh and blood predecessors:

与原有肢体之间的区别在于:

the vast majority of them are painful.

大部分幻肢都带有疼痛感。

To fully understand phantom limbs and phantom pain,

为了全面了解幻肢和幻肢痛，

we have to consider the entire pathway from limb to brain.

我们必须研究从肢体到大脑的整条通道。

Our limbs are full of sensory neurons responsible for everything

我们的肢体上布满了感觉神经元 来对外界做出反应，

from the textures we feel with our fingertips

包括我们指尖感受到的质感

to our understanding of where our bodies are in space.

和对自己身体所处空间位置的理解。

Neural pathways carry this sensory input through the spinal cord

神经通道把这个感官输入从脊髓

and up to the brain.

运输到大脑。

Since so much of this path lies outside the limb itself,

由于通道的大部分都独立于肢体之外，

most of it remains behind after an amputation.

它们都会在截肢后继续存在。

But the loss of a limb

但是失去肢体

alters the way signals travel at every step of the pathway.

会改变信号穿过通道中的每一步过程。

At the site of an amputation,

在截肢的部位，

severed nerve endings can thicken and become more sensitive,

切断的神经末梢会变厚 并且变得更为敏感，

transmitting distress signals even in response to mild pressure.

它即使在温和的刺激下 也会传递痛觉信号。

Under normal circumstances,

在正常情况下，

these signals would be curtailed in the dorsal horn of the spinal cord.

这些信号会在脊髓背角神经元处被截断。

For reasons we don’t fully understand, after an amputation,

出于一些我们还未知的原因，在截肢后

there is a loss of this inhibitory control in the dorsal horn,

脊髓背角处的抑制作用有一定的减弱，

and signals can intensify.

所以痛觉信号就会被放大。

Once they pass through the spinal cord, sensory signals reach the brain.

一旦通过了脊髓这一关， 信号就会被传递至大脑。

There, the somatosensory cortex processes them.

在那里，躯体感觉皮层会处理这些信号。

The entire body is mapped in this cortex.

人的整个身体的知觉都被 这个皮层分区处理。

Sensitive body parts with many nerve endings,

布满神经末梢的敏感部位，

like the lips and hands,

比如说嘴唇和手，

are represented by the largest areas.

占据了最大面积。

The cortical homunculus is a model of the human body

”皮质小人“ 是一种人体模型

with proportions based on the size of each body part’s representation in the cortex,

他的身材比例代表了身体 各个部位在皮层中所占比重，

The amount of cortex devoted to a specific body part can grow or shrink

与身体部分所关联的皮层量 受大脑所接受的感官输入影响

based on how much sensory input the brain receives from that body part.

会增多或者减少。

For example, representation of the left hand is larger in violinists

打个比方，小提琴家的左手比非小提琴家

than in non-violinists.

占据更大面积的皮层。

The brain also increases cortical representation

当身体的一部分受伤时，

when a body part is injured

大脑也会增加这一块皮层的比例，

in order to heighten sensations that alert us to danger.

从而放大这种感官并警告我们远离危险。

This increased representation can lead to phantom pain.

增大的皮层量会造成幻肢痛。

The cortical map is also most likely responsible

皮层地图很有可能让我们

for the feeling of body parts that are no longer there,

不复存在的身体部分有了感知，

because they still have representation in the brain.

因为这些身体部分 还存在于大脑的地图中。

Over time, this representation may shrink and the phantom limb may shrink with it.

久而久之，幻肢也许会因为 皮层减少而消失，

But phantom limb sensations don’t necessarily disappear on their own.

但幻肢痛却不会自己消失。

Treatment for phantom pain usually requires

想要治疗幻肢痛

a combination of physical therapy,

通常需要结合物理治疗、

medications for pain management,

止痛药，

prosthetics,

义肢

and time.

和时间。

A technique called mirror box therapy

有一种治疗方法叫做镜箱治疗，

can be very helpful in developing the range of motion

它能帮助幻肢运动

and reducing pain in the phantom limb.

并减少疼痛感。

The patient places the phantom limb into a box behind a mirror

患者把自己的幻肢放入镜子背后的箱子，

and the intact limb in front of the mirror.

把完好的手放在镜子前，

This tricks the brain into seeing the phantom

这便让患者的大脑误以为 看见了真正的肢体，

rather than just feeling it.

而不只是感觉到它。

Scientists are developing virtual reality treatments

科学家们正在研发虚拟现实治疗，

that make the experience of mirror box therapy even more lifelike.

从而使镜箱治疗更加真实。

Prosthetics can also create a similar effect—

义肢也能产生同样的效果：

many patients report pain

许多患者称

primarily when they remove their prosthetics at night.

他们在晚上卸掉义肢时感到了疼痛。

And phantom limbs may in turn

也许幻肢会帮助这些患者，

help patients conceptualize prosthetics as extensions of their bodies

让他们将义肢视作身体的一部分，

and manipulate them intuitively.

并更轻松地使用自己的义肢。

There are still many questions about phantom limbs.

围绕着幻肢的疑问还有很多，

We don’t know why some amputees escape the pain

我们不知道为什么有些被截肢者

typically associated with these apparitions,

并没有感觉到幻肢的痛，

or why some don’t have phantoms at all.

而有些人甚至完全感受不到幻肢。

And further research into phantom limbs

我们深入研究幻肢，

isn’t just applicable to the people who experience them.

不仅仅是为了帮助有幻肢感的人。

A deeper understanding of these apparitions

对幻肢的深入了解

will give us insight into the work our brains do every day

还能使我们更深入理解大脑的运行方式，

to build the world as we perceive it.

以及大脑怎样建立我们所认知的世界。

They’re an important reminder

这些认识提醒着我们，

that the realities we experience are, in fact, subjective.

我们所经历的现实，一直都是主观上的。