Tue, Apr 23, 2013 - Page 10 News List

Even non-amputees experience‘phantom limbs’
非截肢者也會經驗「幻肢」現象

Afghan amputees practice walking with their prosthetic limbs in Mihtarlam city in Laghman province in Afghanistan on Feb. 23.
二月二十三日,阿富汗截肢者在阿富汗拉格曼省米特拉姆市,練習用義肢行走。

Photo: AFP
照片:法新社

Amputees often experience “phantom limbs,” or the sensation that their missing limb is still present, but a Swedish study published on April 11 showed that even non-amputees can experience the bizarre sensation.

“Our results show that the sight of a physical hand is remarkably unimportant to the brain for creating the experience of one’s physical self,” said the lead author of the study, Arvid Guterstam of Sweden’s prestigious Karolinska Institute.

Phantom limbs can be distressing and painful for amputees, and drugs cannot help as the sensation is essentially a trick of the brain, which imagines the existence of a limb that is not there.

Guterstam said his team hoped the results of their study would help lead to future research on amputees’ phantom pain.

The researchers conducted 11 different experiments creating a perceptual illusion so that volunteers with two arms and hands experienced having an invisible hand.

In the experiments, participants sat at a table with their right arm hidden from their view behind a screen.

A scientist then touched the participant’s right hand with a paintbrush while imitating the exact movements with another paintbrush in mid-air within the participant’s full view.

“We discovered that most participants, within less than a minute, transfer the sensation of touch to the region of empty space where they see the paintbrush move, and experience an invisible hand in that position,” Guterstam said.

“Previous research has shown that non-bodily objects, such as a block of wood, cannot be experienced as one’s own hand, so we were extremely surprised to find that the brain can accept an invisible hand as part of the body,” he added.

TODAY’S WORDS 今日單字

1. bizarre adj.

怪異的 (guai4 yi4 de5)

例: Have you ever experienced the bizarre phenomenon of sleep paralysis?

(你有沒有經歷過鬼壓床的這種怪異現象?)

2. trick n.

花招 (hua1 zhao1)

例: Many realtors use various tricks to sell houses.

(許多房仲業者運用各種賣房花招。)

3. illusion n.

幻覺 ((huan4 jue2)

例: He’s not really a good person. It’s just an illusion.

(這只不過是你的幻覺,但他不真是個好人。)


In another experiment, researchers made a stabbing motion with a knife toward the empty space “occupied” by the invisible hand and measured the participant’s sweat response in their palms to the perceived threat.

They found that the participants’ stress responses were higher when they experienced the illusion, but absent when the illusion was broken.

In a third experiment, the volunteers were asked to close their eyes and point with their left hand to their right hand. After having experienced the illusion for a while, they pointed to the location of their invisible hand instead of the real hand.

Researchers also measured brain activity, and found that the invisible hand illusion led to increased activity in the parts of the brain that are normally active when individuals see their real hand being touched.

Seventy-four percent of the 234 volunteers experienced a phantom limb during the experiments, Guterstam said.

The results were published on April 11 in the US Journal of Cognitive Neuroscience.

(AFP)

截肢者經常經驗「幻肢」現象,意即截肢者覺得失去四肢仍然健在的感知。但是刊登於四月十一日的一篇瑞典研究發現,即便是無截肢者,亦可經驗此怪異的感覺。

該研究主筆、瑞典著名卡羅琳斯卡醫學院研究員阿維德‧古德斯塔姆表示:「我們的研究結果顯示,一隻手的存在與否,對於腦部創造人們自身肢體的經驗來說,並不重要。」

幻肢可能令截肢者感到苦痛,而這種基本上是腦部創造的假象—也就是腦部將不存在的四肢想像成是存在的—是無法靠藥物減緩的。

古德斯塔姆表示,其團隊期望此結果將有助未來關於截肢者幻肢痛的研究。

研究員做了十一項不同的試驗,藉由創造認知幻覺,讓有一雙上肢與手的受試者,經驗到還有另一隻看不到的手。

在試驗中,受試者坐在桌前,並將其右上肢藏於螢幕後方視線看不到之處。

隨後,一位研究者以畫筆碰觸受試者的右手,同時再用另一枝畫筆於受試者的全視線下,在空中做出同樣動作。

古德斯塔姆說:「我們發現大多數的受試者在一分鐘內,把被碰觸的感覺,傳達到他們眼見畫筆揮動的空中,並感覺有隻隱形手在那裡。」

他補充道:「先前有研究顯示,像是一塊木頭等的物體,是無法被經驗成是一個人的手;也因為如此,當我們研究結果發現大腦可以將一隻看不到的手視為身體的一部分,我們感到極為驚訝。」

在另一項試驗中,研究者以刀子對著這個隱形手所在的空間,做出刀刺動作,並在受試者意識到此威脅時,測量其手心冒汗反應。

他們發現受試者在經驗這項幻覺時,壓力反應更大,而當幻滅時,此壓力即消失。

在第三個試驗中,受試者被要求闔眼,並用左手指向他們的右手。在經驗幻覺一陣子後,他們指向的不是他們真正的手,而是指著那隻隱形手。

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