雖然失去了嗅覺神經(jīng)，但仍能聞到氣味

這些女人雖然失去了嗅覺神經(jīng)，但仍能聞到氣味

Fresh-baked bread. Rain falling onto warm soil. Cut grass in the summer. We can relish in these fragrances thanks to a bundle of nerves deep inside each nostril called an olfactory bulb - or so we thought, anyway.

新鮮的烤面包、雨水落在溫暖的土壤上、夏天割草。我們可以享受這些香味，這要?dú)w功于每個鼻孔深處的一束神經(jīng)，叫做嗅球——至少我們是這么認(rèn)為的。

Among brain scans from over 1,000 subjects, researchers have now identified a handful of cases where individuals appear to lack this structure. Nevertheless, these people can identify smells surprisingly well.

在對1000多名受試者的腦部掃描中，研究人員現(xiàn)在發(fā)現(xiàn)了少數(shù)人似乎缺乏這種結(jié)構(gòu)。然而，這些人卻能很好地辨別氣味。

Neurologists from the Weizmann Institute of Science in Israel and the Florey Institute of Neuroscience and Mental Health in Australia initially stumbled across two strange cases of missing olfactory bulbs while reviewing MRIs for a different study.

以色列魏茨曼科學(xué)研究所(Weizmann Institute of Science)和澳大利亞弗洛里神經(jīng)科學(xué)與心理健康研究所(Florey Institute of Neuroscience and Mental Health)的神經(jīng)學(xué)家在為另一項研究進(jìn)行核磁共振檢查時，最初偶然發(fā)現(xiàn)了兩個奇怪的嗅球丟失病例。

Since their research required left-handed female volunteers with a sense of smell, the absences stood out as particularly odd, warranting further investigation.

由于他們的研究需要有嗅覺的左撇子女性志愿者，這些缺席顯得特別奇怪，值得進(jìn)一步調(diào)查。

The olfactory bulbs, located deep inside most of our skulls, could be described as a pair of upside-down toothbrushes. Their handles reach back into our brain, and their bristles poke into the roof of our nasal cavities.

嗅球位于我們大多數(shù)頭骨的深處，可以說是一對倒置的牙刷。它們的手柄伸進(jìn)我們的大腦，鬃毛伸進(jìn)我們的鼻腔。

The purpose of this bulb of sensory nerves is to catch volatile particles floating about in the air we inhale and send messages into various parts of the brain, including sections responsible for memory and emotion.

這種感覺神經(jīng)球的目的是捕捉漂浮在我們吸入空氣中的揮發(fā)性顆粒，并將信息發(fā)送到大腦的各個部分，包括負(fù)責(zé)記憶和情感的部分。

The result can fill us with pleasure or disgust, summoning memories of fear or recollection of grandma's hugs. If this is the olfactory bulb's function, it stands to reason that should it be damaged – or missing altogether – our ability to detect any trace of a scent should be seriously affected.

結(jié)果會讓我們充滿愉悅或厭惡，喚起恐懼的回憶或是對祖母擁抱的回憶。如果這是嗅球的功能，那么如果它被損壞或者完全丟失，我們探測氣味痕跡的能力應(yīng)該受到嚴(yán)重影響。

Yet controversial studies on rodents raise some interesting questions. Even when olfactory bulbs have been eaten away by lesions, or removed altogether, researchers have found their lab animals could still respond to scent-oriented tasks.

然而，關(guān)于嚙齒動物的有爭議的研究提出了一些有趣的問題。即使嗅球被病變吞噬，或者被完全移除，研究人員發(fā)現(xiàn)他們的實驗動物仍然可以對氣味導(dǎo)向的任務(wù)做出反應(yīng)。

Unfortunately, lab animals are crafty subjects, who might find ways to navigate that test for a tasty treat – smell or no smell. That leaves plenty of room for doubt over whether such results should be taken seriously

不幸的是，實驗動物是狡猾的實驗對象，他們可能會想辦法在測試中找到美味的食物——聞或不聞。這就給人們留下了很大的懷疑空間，懷疑是否應(yīng)該認(rèn)真對待這樣的結(jié)果。

Having now stumbled across two volunteers who had no olfactory bulbs and still seemed to have a sense of smell, neurologists had an opportunity.

現(xiàn)在，在無意中發(fā)現(xiàn)了兩個志愿者，他們沒有嗅球，但似乎仍然有嗅覺，神經(jīng)學(xué)家有了一個機(jī)會。

In spite of what you might think, we humans are pretty good smellers, discriminating between maybe as many as a trillion different odours. And, unlike rats, people can be quizzed on their experiences.

不管你怎么想，我們?nèi)祟惖男嵊X很好，分辨出的氣味可能多達(dá)一萬億種。而且，與老鼠不同的是，可以問到他們的經(jīng)歷。

So the research team used their unexpected finds as a starting point to hunt down more examples in a massive public collection of MRIs aimed at mapping connections in the human brain.

因此，研究小組以他們意想不到的發(fā)現(xiàn)為起點，在一個旨在繪制人類大腦連接圖譜的大規(guī)模公共核磁共振成像集合中，尋找更多的例子。

Sifting through 1,113 scans, they uncovered a further three.

通過1113次掃描，他們又發(fā)現(xiàn)了3例。

The new examples were also all women, with one also being left-handed. It's not at all clear what these biases mean, but the fact that the records all reported they had a sense of smell was startling.

新的例子也都是女性，其中一個也是左撇子。目前還不清楚這些偏見意味著什么，但記錄顯示他們都有嗅覺，這一事實令人震驚。

To confirm suspicions, the team went back to their original two volunteers and recruited a third woman who lacked olfactory bulbs but also happened to have anosmia – an inability to detect scents.

為了證實這一懷疑，研究小組又找來了最初的兩名志愿者，并招募了第三名女性志愿者。這名女性沒有嗅球，但碰巧也患有嗅覺缺失癥，即無法察覺氣味。

More detailed scans of the volunteers' brains found their entire olfactory bulb structures were indeed diminished. The team concluded that they had to be tiny, if the women had any olfactory bulbs at all.

對志愿者大腦的更詳細(xì)掃描發(fā)現(xiàn)，他們的整個嗅球結(jié)構(gòu)確實被削弱了。研究小組得出結(jié)論，如果這些女性身上有嗅球，那么她們的鼻子就必須很小。

They then gave the women a whiff of 10 odorants and asked them to rate them according to 11 different descriptors. Their results were compared with those taken from 140 other women who all had completely functional olfactory bulbs.

然后，研究人員給這些女性聞了10種氣味，并要求她們根據(jù)11種不同的描述對這些氣味進(jìn)行評級。研究人員將他們的研究結(jié)果與另外140名擁有完全正常功能的嗅球的女性的研究結(jié)果進(jìn)行了比較。

The results provided by the two bulb-less women who could still smell were remarkable, but only in that they shouldn't have the ability to smell at all.

兩位沒有嗅球的女性提供的結(jié)果是顯著的，但僅僅是她們不應(yīng)該有嗅覺的能力。

There was one other curiosity. The descriptors they each provided were eerily similar to one another's.

還有一件怪事。他們各自提供的描述符出奇地相似。

It's hard to tell exactly what's going on, and what – if any – olfactory nerves these women might have retained. But it does reinforce the notion that our brains are capable of doing a lot with very little.

很難確切地說出到底發(fā)生了什么，以及這些女性可能保留了什么(如果有的話)嗅覺神經(jīng)。但它確實強(qiáng)化了這樣一種觀念，即我們的大腦可以用很少的東西做很多事情。

"The simplest interpretation of our findings is that these women were born without an olfactory bulb, but thanks to the extreme plasticity of the developing brain, they developed an alternative glomeruli map somewhere else in the brain, not in the olfactory bulb," says Sobel.

索貝爾說：“對于我們的發(fā)現(xiàn)，最簡單的解釋是，這些女性出生時沒有嗅球，但由于發(fā)育中大腦的極度可塑性，她們在大腦的其他地方，而不是嗅球中，形成了另一種腎小球圖。”。

This research was published in Neuron.

這項研究發(fā)表在《神經(jīng)元》雜志上。