STUDENTS facing exams this month, take heart: your companions can smell your fear, and they empathise.

    That's the implication of a study by Bettina Pause at the University of Dusseldorf, Germany, and colleagues. They put absorbent pads under the armpits of 49 university students an hour before they took their final oral exam and again as the same students exercised. Another set of students then sniffed the sweat samples while having their brains scanned.

    None perceived a difference between the two types of sweat, but the pre-exam sweat had a different effect on brain activity, lighting up areas that process social and emotional signals, as well as several areas thought to be involved in empathy （PLoS One, DOI: 10.1371/journal.pone.0005987）.

    The researchers conclude that anxiety prompts the release of a chemical that bypasses conscious experience, automatically triggering similar feelings in anyone who sniffs it. This may allow fear to spread quickly and speed our ability to flee danger. A previous experiment found that sweat from skydivers activated anxiety circuits in sniffers' brains.

    學生們本月要面臨考試，鼓起勇氣吧：你的同伴可以聞出你的恐懼來，他們也會產生同樣的恐懼。

    這是德國杜塞爾多夫大學的貝蒂娜·鮑絲與其同事所做一項研究的結論。他們在49位大學生參加期終口試之前，把吸水巾在學生的腋下放置一個小時，在這些學生參加書面考試之前再做同樣的測試。另一組學生隨后嗅聞這些取樣的汗水，同時對這組學生的大腦進行掃描。

    無人理解這兩種汗水有何區別，但前一種考試的汗水對大腦活動的影響有所不同，它會使處理社會和情感信號的腦域興奮起來，也會使若干被認為與同情有關的腦域興奮起來（《公共科學圖書館綜合》，文章號碼： 10.1371/期刊。發行條碼0005987）.

    研究人員得出的結論是，焦慮不安會引起一種化學物質的釋放，這種化學物質繞過神志清醒的感受，可以自動觸發嗅聞者的同類情緒。這可能讓恐懼迅速蔓延，并讓我們能夠加速逃離危險。此前的實驗發現，高空跳傘運動員的汗水會激活嗅聞者大腦中的焦慮神經。