Pole position: human body might be able to pick up on Earth’s magnetic field 朝向地球極點起跑 人體可能感知地球磁場

TODAY’S WORDS
今日單字

1. magnetic field phr. 磁場
2. magnetoreception n.地磁感應

3. electromagnetic adj.電磁的

4. pole n.地球極點

5. equator n.赤道 (chi4 dao4)

6. within the realm of possibility adj.有可能的

It sounds like a power to be boasted of by the X-Men, but researchers say humans might have the ability to pick up on Earth’s magnetic field. Many animals, from pigeons to sea turtles, use it to navigate, while research has shown cattle prefer to align themselves with the field when standing in, well, a field. Even dogs make use of it — albeit when defecating. 雖然聽起來很像X戰警誇耀的特殊能力，不過科學家近日指出，人類可能具有感知地球磁場的能力。從鴿子到海龜，許多動物會使用這種能力導航，也有研究顯示，當牛隻在牧場中站立不動時，排列方向會傾向於朝向磁場校準，甚至是狗也會運用這種能力，不過是在排便的時候。

But while debates continue about the mechanisms behind such phenomena, it has remained unclear whether humans also have the power of magnetoreception. Now scientists say there are signs that we do. “We have not as a species lost the magnetic sensory system that our ancestors [millions of years ago] had,” said Joseph Kirschvink, leader of the research from the California Institute of Technology. “We are part of Earth’s magnetic biosphere.” 學界對此現象背後的機制仍爭論不休，也無法確定人類是否也有地磁感應的能力，不過科學家近日表示，有跡象顯示人類具備這種能力。這項研究由加州理工學院進行，計畫主持人約瑟夫‧柯許溫克教授指出：「我們人類，以一個物種而言，並未失去我們祖先（數百萬年前）具備的磁感應系統」，「我們是感應地球磁場的生物圈一份子。」

Writing in the journal eNeuro, Kirschvink and colleagues in the US and Japan describe how they made their discovery after building a six-sided cage, the walls of which were made of aluminum to shield the setup from electromagnetic interference. These walls also contained coils through which currents were passed to produce magnetic fields of about the same strength as Earth’s. Each participant was asked to enter the cage and sit still on a wooden chair in the dark, facing straight ahead toward the north. During the experiment, the team measured the participant’s brain waves using an electroencephalogram (EEG). 在這篇發表於美國神經科學學會線上期刊《eNeuro》的研究中，柯許溫克和美國與日本的同事描述他們如何獲得這項發現：他們建造一個六面的立方體籠子，牆面由鋁打造，保護這項設施不受電磁干擾影響。牆壁中埋有電線，電流通過後遂產生磁場，磁力約等同於地球磁場。每位受試者被要求進入籠子，在黑暗中坐在一張木椅上維持不動，面朝北方。實驗過程中，研究團隊會用腦電波圖量測受試者的腦波。

In some experiments, the applied magnetic fields were fixed in one direction, while in others they were rotated. In still others, the machines were turned on but no magnetic field was produced — meaning the participant was only exposed to Earth’s natural magnetic field. The participant was unaware of which experiment was underway. 在其中幾次實驗中，人為設定的磁場會固定在單一方向；其他幾次實驗中，磁場則會旋轉。在另外幾次實驗中，儀器是開啟的，但並未製造出磁場，也就是讓受試者單純暴露在地球的自然磁場中。受試者都不知道目前正在進行哪一種實驗。

The results, gathered from 34 adult participants, revealed that certain scenarios triggered a drop in participants’ alpha brain waves — a change that is linked to the brain processing information. This occurred if the applied magnetic field was pointed north and then swept upwards or downwards, or directed down while pointing north and rotated anticlockwise. That is similar to a human in the northern hemisphere nodding their head, or turning their head to the right respectively. 從三十四名成年受試者獲得的結果顯示，某些特定情況會觸發大腦的阿爾法波降低，而阿爾法波的變化和大腦處理資訊有關。這個變化會發生磁場設定指向北，然後上下晃動，或是磁場指向北，但卻向下傾斜，同時逆時鐘旋轉。這兩種設定分別相似於人類在北半球點頭，或是向右轉頭。

Kirschvink said the responses are akin to the brain “freaking out” — in other words clocking an unexpected change in the environment. Crucially, he said, it means that humans must be able to detect such changes — although the strength of the response varied hugely among participants. The team says the experiments offer clues as to what the human magnetoreception system might look like — noting that the results rule out electrical induction, or simply artifacts, as explanations. 柯許溫克表示，這類反應近似於腦袋「突然異常」，換言之，就是大腦感應到環境中發生意料之外的變化。他說，重要的是這表示人類一定能偵測這種變化，只是受試者彼此間的反應強度大相逕庭。研究團隊認為，這項實驗提供線索，有助了解人類的地磁感應系統可能會是什麼模樣，並且註明實驗結果排除電感應和干擾波的解釋。

One possible system that has been mooted for other animals, particularly birds, is a “quantum compass” based on molecules with unpaired electrons that respond to Earth’s magnetic field. This would allow an animal to tell whether they are moving toward a pole or the equator, but not whether they are headed north or south. But authors say the new research suggests the human system can tell north from south, supporting an alternative mechanism involving special cells containing iron-based crystals. These crystals are thought to rotate rather like the needle of a compass, opening or closing pores in the cells, thereby affecting signals being sent to the brain. 在其他動物身上──特別是鳥類──已被提出來討論的一種可能系統是「量子羅盤」，藉由分子內的不成對電子對應地球磁場。這個系統讓動物可以判斷他們是往地極或是赤道移動，但無法辨識前進方向是往南還是北。不過，作者群認為，這份新研究顯示人類的系統可以分辨南北，並且支援由含有鐵基晶體的特殊細胞參與運作的另一種機制。這類晶體被認為會像羅盤上的指針那樣旋轉，從而開啟或關閉細胞中的孔洞，進而影響傳送給大腦的訊號。

"We are specifically predicting [these cells'] existence — they have to be there," said Kirschvink. As all of the participants came from the northern hemisphere, the idea goes that their cells might have become tuned to its magnetic field — hence the team says modern environments would likely interfere with this "sense," while there is no sign as yet that such a system is linked to human consciousness, or that it influences our behavior — although the team says it remains a possibility, and are planning experiments to find out. 柯許溫克表示：「我們特別預測（這些細胞）確實存在──它們一定就在那裡。」由於全數受試者皆來自北半球，他們的細胞也因此被認為可能已調整朝向北半球的磁場──所以具備分辨南北極的能力。研究團隊指出，現代生活環境有可能干擾這種「感覺」，不過目前還沒有跡象顯示這個系統和人類意識有關，或是它會對我們的行為產生影響。儘管如此，研究團隊仍然不排除這個可能性，也計畫進行實驗找出答案。

Peter Hore, an expert on magnetoreception from the University of Oxford, welcomed the study but said the experiments need to be repeated, including on people from the southern hemisphere, to confirm the findings. Kenneth Lohmann, an expert in magnetoreception from the University of North "Given that a number of other animals can sense Earth's magnetic field, it is certainly within the realm of possibility that humans can as well," he said. However, he also urged caution "It is one thing to find a subtle change in brain activity in response to a weak magnetic field and another thing to show that people really detect and use magnetic field information in a meaningful way." 牛津大學的地磁感應專家彼得‧侯爾對這份研究表示歡迎，不過他也指出實驗需要重複施作，加入南半球的受試者，才能證實這些發現。北卡羅萊納大學教堂山分校的地磁感應專家肯尼斯‧羅曼則認為，這份研究既吸引人又發人深省。他表示：「有鑑於其他多種動物可以感覺到地球磁場，人類有這種能力完全是有可能的。」不過他也呼籲研究需謹慎行事：「在腦部活動中找到一個細微的變化，會對磁性弱的磁場產生反應，這是一回事，但是要證明人類真的可以偵測到、並且有意義地運用磁場的資訊，又是另一回事。」

(The Guardian)（台北時報章厚明譯）