What It’s Like to Have Face Blindness患臉盲癥是怎么回事

丹尼爾·吉布斯 王昊堃

Recently， while out walking my dog Jack， I encountered a blond woman pushing a toddler in a stroller while walking her dog. I stopped to chat， asking her how old her son was now， and she responded amiably. About a year and a half ago， three women on our block gave birth within a month of each other. One woman has blond hair and two have dark hair. They all have dogs. As soon as we had ended our chat and I was walking on， I realized that she had the wrong dog. The blond on our block has a black lab1， and this dog was some kind of curly-haired terrier2. I then realized that the woman I had approached was a complete stranger， not one of my neighbors.

On the face of it， this wouldn’t be a particularly noteworthy incident， given the context of the COVID pandemic that has so many of us wearing masks. It has become a common， shared experience， these awkward social moments in which we’ve failed to recognize people we know， or we’ve been on the receiving end3 of someone we know looking right past us as if we’re strangers. But the moment held more for me.

I am a retired neurologist. I also have early-stage Alzheimer’s disease. During my 25 years practicing general neurology in Portland， Ore.， I took care of many patients with dementia， including Alzheimer’s disease. I never suspected that I too might get Alzheimer’s， but then about 15 years ago I started to lose my sense of smell and began to experience stereotypical phantom odors called phantosmias4. Problems with smell can be early symptoms of neurodegenerative5 diseases like Alzheimer’s， but it was another six or seven years before I started to have issues with my memory. The neuropathology6 of Alzheimer’s disease， the beta-amyloid plaques7 and tau-containing neurofibrillary tangles， are found first in olfactory centers in the brain， years before cognitive impairment begins. As part of a research study， I underwent amyloid and tau PET8 scans of my brain in 2015 and again in 2018， and the scans confirmed the diagnosis and progression of Alzheimer’s disease.

Being a neurologist with a neurological disorder has provided me some special insights. For example， seeing beta-amyloid on my first amyloid PET scan located not only in the prefrontal cortex9 and precuneus10 but also in olfactory processing centers such as the piriform cortex11 and orbital frontal cortex12 was really exciting because it provided a logical explanation for my olfactory problems. The PET scans also gave me some hints as to the cause of my trouble recognizing my neighbors.

Face blindness， or prosopagnosia13， is a neurological condition resulting in trouble identifying human faces. It is usually caused by damage to the fusiform gyrus14 in the posterior temporal lobe15 and anterior16 portion of the occipital lobe17. Neurologist-author Oliver Sacks famously introduced this condition to popular culture in his 1985 book The Man Who Mistook His Wife for a Hat. Sacks wrote about his own severe face blindness in a wonderful， August 23， 2010， article in the New Yorker. One of my neurologist colleagues has such severe face blindness that she needs to hear someone speak before reliably making an identification. Like Sacks， she’s had it all her life. Up to 2.5 percent of people are born with congenital18 face blindness， mostly inherited in an autosomal19 dominant pattern.

Acquired face blindness may be caused by head trauma， strokes or tumors affecting the fusiform gyrus. A more insidious20 form of face blindness occurs in many people with Alzheimer’s disease， even in the early stages. The tau-containing neurofibrillary tangles of Alzheimer’s disease usually first occur in the medial21 portion of the anterior temporal lobes. With time， these neurofibrillary tangles can spread backwards into the fusiform gyrus.

Although my cognitive impairment is still mild， I have been having increasing trouble recognizing faces， even of people I know well. Many of my neighbors are hard for me to recognize until I hear their voices or see the dog they are walking. Before the pandemic， I would often be embarrassed by not recognizing or misidentifying an acquaintance while walking my dog.

Our masks are now covering important facial features used for facial recognition. A recent study from York University in Toronto and Ben-Gurion University in Israel confirmed this by demonstrating “quantitative and qualitative changes in the [visual] processing of masked faces” that “could have significant effects on activities of daily living.” Perhaps everyone now is experiencing a degree of face blindness.

The ability to accurately identify other people by recognizing their faces is important to our social， emotional and cultural behaviors. Our brains appear to learn how to recognize the faces of other people of our race during childhood. A study in 2019 showed that there is a critical period for this learning. Children learn how to recognize faces of the group they are raised with， up until about age 12. White children will become adept at distinguishing white faces， but unless they are exposed to other racial faces， they will have trouble distinguishing people of other races.

Similarly， an Asian child raised in an Asian country without exposure to white faces will not be able to distinguish white faces. An Asian child adopted and raised in a predominantly white country will distinguish white faces but not Asian faces. A child who grows up in a racially heterogeneous22 setting will be able to distinguish faces of all of those races. This learning process slows down and then is gone by age 12.

To me this implies that there are pathways in the brain， probably in the fusiform gyrus， that are developing new neuronal23 connections during childhood as we learn what makes one face look different from another， but that this plasticity24 is lost by age 12. It strikes me that while face masks are drawing our attention to the subject of face blindness， more relevant may be the impact of our children’s social exposure that supports how they see others， literally， in our diverse communities.

I’ll need to attend closely to those masked faces to overcome my combined disadvantage of neurological face blindness and masked face blindness， the first caused by abnormalities of the brain and the second simply due to the blocking of visual cues. My best option may be to pay closer attention to the dogs. Even for me， pets are easy to identify because of shape， size， color of coat and sometimes temperament or behavior. I’ll also need to expand my mental dog gallery now to include that curly terrier and his friendly human companion with the baby stroller. Next time we pass on the street， we’ll be strangers no more.

最近，我在遛狗狗杰克時，遇見了一位同在遛狗的金發(fā)女士，她推著嬰兒車，車里坐著一個看樣子正在學步的小男孩。我停下來與她交談，問她兒子多大了，她友善地回應了我。大約一年半前，我們街區(qū)有三位女士在一個月內(nèi)先后生了孩子，她們當中一人是金發(fā)，兩人是黑發(fā)，并且三人都養(yǎng)狗。就在我們剛剛結(jié)束聊天、我繼續(xù)往前走時，我意識到這只狗并不是她的。我們街區(qū)那位金發(fā)女士養(yǎng)了一只黑色的拉布拉多，而這只是一種卷毛小獵狗。我恍然大悟，剛剛與我交談的女士完全是個陌生人，并非我那三位鄰居之一。

表面看來，在許多人因新冠疫情都要佩戴口罩的情況下，這并不是一件多么值得注意的事。我們沒能認出認識的人，或是認識的人沒能認出我們，如同面對陌生人，這些社交場合的尷尬瞬間已經(jīng)成了人人都有的經(jīng)歷。但這一刻對我來說卻有著非同尋常的意義。

我是一名退休的神經(jīng)學家，患有早期阿爾茨海默病。我在俄勒岡州波特蘭市從事普通神經(jīng)學研究已有25年，其間治療過許多患有包括阿爾茨海默病在內(nèi)的癡呆病人。我從未想到自己會患上阿爾茨海默病。然而，大約15年前，我開始失去嗅覺，典型的癥狀就是會聞到實際上并不存在的臭味，這叫“嗅幻覺”。嗅覺出現(xiàn)問題可能是阿爾茨海默病之類的神經(jīng)退行性疾病的早期癥狀，而我的記憶開始出現(xiàn)問題是六七年之后的事了。阿爾茨海默病的神經(jīng)病理學表明，在人體發(fā)生認知障礙的幾年前，大腦嗅覺中樞就已經(jīng)存在β-淀粉樣斑塊和含tau蛋白的神經(jīng)原纖維纏結(jié)。我在2015和2018年先后做了兩次“派特”，檢測腦部的淀粉樣蛋白和tau蛋白含量，這也是一次研究的組成部分。掃描確診我患上了阿爾茨海默病，并且顯示病情在惡化。

作為一名神經(jīng)學家，患上神經(jīng)功能障礙倒是讓我有了一些獨到的認識。比如，我的第一張淀粉樣蛋白派特圖顯示，β-淀粉樣蛋白不僅位于前額皮層和楔前葉，同時還存在于梨狀皮層和眶額皮層等嗅覺處理中樞。我對此格外興奮，因為這樣，我的嗅覺問題就解釋得通了。派特掃描還給了我一些線索，幫助我找到認不出鄰居的原因。

臉盲，也叫面容失認癥，是一種神經(jīng)系統(tǒng)疾病，具體表現(xiàn)為辨別人臉困難，通常由后顳葉和枕葉前部梭狀回損傷導致。眾所周知，神經(jīng)學家兼作家奧利弗·薩克斯在其1985年的著作《錯把妻子當帽子》中將這一疾病引入大眾文化。2010年8月23日發(fā)行的《紐約客》曾刊登過薩克斯的一篇精彩文章，其中就寫到他自己患有嚴重的臉盲癥。我的一位神經(jīng)學家同事也有嚴重的臉盲癥，她需要聽到對方說話才能確認此人的身份。和薩克斯一樣，臉盲癥伴隨了她一生。高達2.5%的人患有先天性臉盲癥，其中大多數(shù)是常染色體顯性遺傳所致。

導致后天臉盲癥的原因可能是頭部創(chuàng)傷、中風或腫瘤影響到了梭狀回。臉盲癥還會以一種更加隱蔽的方式存在于許多阿爾茨海默病患者體內(nèi)，甚至病程早期就已存在。阿爾茨海默病的含tau蛋白的神經(jīng)原纖維纏結(jié)通常首先出現(xiàn)在前顳葉中部。隨著時間推移，這些神經(jīng)原纖維纏結(jié)會向后蔓延至梭狀回。

我的認知障礙不算太嚴重，但在認人方面卻越來越困難，甚至包括熟人。許多鄰居我已經(jīng)很難辨認，除非聽到他們的聲音或看到他們遛的狗。疫情之前，我在遛狗時，常會因為認不出或認錯人而感到尷尬。

戴上口罩，識別人臉所需的幾項重要面部特征便被遮住了。加拿大約克大學和以色列本·古里安大學近期的一項研究演示了“大腦對戴上口罩的人臉進行（視覺）處理時量和質(zhì)的變化可能給日常生活中的各類活動帶來顯著影響”，由此證實了這一點?；蛟S我們每個人都正在體驗一定程度的臉盲。

通過辨認人臉來準確識別人，這一能力對于我們的社交、情感及文化行為都非常重要。我們的大腦似乎在幼年時就學著如何辨認同一種族其他人的臉了。2019年的一項研究表明，辨認人臉的學習有一段關(guān)鍵時期。一直到12歲左右，兒童都在學習如何辨認他們成長過程中身邊人的臉。白人兒童會變得擅長辨認白種人的臉，而辨認其他種族人的臉就會有難度，除非與其他種族的人共處。

同樣，一個在亞洲國家長大的亞洲兒童，如果不與白種人共處，就不會辨認白種人的臉。一個亞洲兒童被領(lǐng)養(yǎng)并在以白種人為主的國家長大，就會辨認白種人的臉，卻不會辨認亞洲人的臉。一個在多種族混居環(huán)境中長大的孩子將會辨認所有相關(guān)種族人的臉。學習辨認人臉的過程在12歲之前會逐漸減緩，直至消失。

對我來說，這意味著大腦中——很可能就在梭狀回中——存在著一些通路，我們在孩童時期學習辨認不同人臉的區(qū)別時，這些通路就在不斷建立新的神經(jīng)元連接，不過這種可塑性到12歲就消失了?？谡忠鹆宋覀儗δ樏み@個話題的關(guān)注，但我認為更有意義的或許是，在這個多元化的社會里，接觸的群體與環(huán)境對孩子們發(fā)展認人能力的影響。

我得密切注意那些戴著口罩的路人，以便克服我的兩個弱點：一個是因大腦異常導致的神經(jīng)學意義上的臉盲，而另一個僅僅是因面部特征被遮擋導致的臉盲。對我來說，最佳的選擇或許是給予狗狗們更密切的關(guān)注。因為即便對于我這種認臉有困難的人，也可以根據(jù)體形、塊頭、皮毛顏色，以及脾氣或行為，輕易辨認出不同的寵物。同時，我也要擴充我腦海中的狗狗圖庫，把那只卷毛小獵狗加進去，還有它那位友善的推著嬰兒車的人類伙伴。下次在大街上相遇，我們便不再是陌生人。

（譯者為“《英語世界》杯”翻譯大賽獲獎者）

1 lab = labrador拉布拉多獵犬。? 2 terrier?犬，一種活潑的小狗。

3 be on the receiving end遭受，承受（不愉快的事）。? 4 phantosmia嗅幻覺，指患者通常會聞到排泄物或下水道的味道。? 5 neurodegenerative神經(jīng)退行性的。? 6 neuro-pathology神經(jīng)病理學。? 7 beta-amyloid plaque β-淀粉樣斑塊。? 8 = Positron Emission Computed Tomography正電子發(fā)射型計算機斷層顯像，是核醫(yī)學領(lǐng)域比較先進的臨床檢查影像技術(shù)。

9 prefrontal cortex前額皮層。? 10 precuneus楔前葉。? 11 piriform cortex梨狀皮層。? 12 orbital frontal cortex眶額皮層。? 13 prosopagnosia面容失認癥。? 14 fusiform gyrus梭狀回，大腦顳葉及枕葉之間的皮層，最主要的作用是識別人臉。普通人看到人臉時，其神經(jīng)活躍度會變高。? 15 posterior temporal lobe后顳葉。? 16 anterior前部的。? 17 occipital lobe枕葉。

18 congenital先天性的。? 19 autosomal常染色體的。? 20 insidious潛伏的。? 21 medial中間的，平均的。

22 heterogeneous各種各樣的，混雜的。

23 neuronal神經(jīng)元的，神經(jīng)細胞的。? 24 plasticity可塑性，適應性。

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