The experiment was not for the squirmish. Volunteers were made to itch like crazy on one arm, but not allowed to scratch. Then they were whisked into an M.R.I. scanner to see what parts of their brains lit up when they itched, when researchers scratched them and when they were finally allowed to scratch themselves.
首先要申明的是，做这个实验可不是要存心折磨人——研究人员通过某些手段致使志愿者们一条手臂痒得发疯，却不允许他们用任何方式挠痒。然后再将他们送入磁共振(MRI)扫描仪，观察他们感到痒痒时，当研究人员帮他们挠痒，以及当他们终于得以自己挠痒时，他们的大脑中分别有哪些部位处于活跃状态。
The scientific question was this: Why does it feel so good to scratch an itch?
这项研究所要解决的科学问题是：为什么挠痒的感觉这么爽？
"It's quite intriguing to see how many brain centers are activated," said Dr. Gil Yosipovitch, chairman of dermatology at the Temple University School of Medicine and director of the Temple Center for Itch (he conducted the experiment while working at Wake Forest School of Medicine). "There is no one itch center. Everyone wants that target, but it doesn't work in real life like that."
“观察有多少大脑中枢受到激活，这差事相当有趣，”美国天普大学医学院(Temple University School of Medicine)的皮肤学系主任，天普大学瘙痒中心(Temple Center for Itch)主任吉尔·杨斯波维奇(Gil Yosipovitch)博士说。（他在威克森林大学[Wake Forest School of Medicine]工作时已经开展这项实验）。“大脑中并没有一个专门的瘙痒中枢。当然大家都希望能有这样一个靶标可以用来对付瘙痒，可现实并不总能尽如人意。”

Instead, itching and scratching engage brain areas involved not only in sensation, but also in mental processes that help explain why we love to scratch: motivation and reward, pleasure, craving and even addiction. What an itch turns on, a scratch turns off — and scratching oneself does it better than being scratched by someone else. The study results were published in December in the journal PLOS One.
与人们的期望相反，瘙痒和挠痒不仅与脑部感觉区有关，还涉及了某些心理过程，譬如：动机和奖赏、愉悦、渴求乃至成瘾等，这就从一定程度上解释了人们喜欢挠痒的原因。挠痒可以关闭那些被瘙痒激活的脑部活动，而且，自己挠痒痒的效果往往优于别人代劳。这些研究结果发表在12月的《公共科学图书馆：综合》杂志(PLOS One)上。
Itching was long overshadowed by pain in both research and treatment, and was even considered just a mild form of pain. But millions of people suffer from itching, and times have changed. Research has found nerves, molecules and cellular receptors that are specific for itching and set it apart from pain, and the medical profession has begun to take it seriously as a debilitating problem that deserves to be studied and treated.
长期以来，无论是在研究领域还是治疗领域，瘙痒作为一个课题总是被另一个课题——疼痛抢尽了风头，甚至，人们一度以为瘙痒只是疼痛的一种较为温和的形式。然而，全球遭受瘙痒之苦的患者已达数百万之多，时代也已经发生了变迁。研究发现，瘙痒具有其特异性的神经、分子和细胞受体，这将它与疼痛区分开来。医学界已经认识到瘙痒也可以削弱人的身体，并开始将其作为一个值得研究和治疗的问题认真对待。
Within the last decade, there has been a flurry of research into what causes itching and how to stop it. Along with brain imaging, studies have begun to look at gene activity and to map the signals that flow between cells in the skin, the immune system, the spinal cord and the brain.
在过去的十年里涌现出了一系列的研究，探讨了引起瘙痒的原因以及如何才能阻止瘙痒。在脑成像技术的帮助下，现在的研究日益关注有关基因的活性，并试图去捕捉和描述那些在皮肤细胞、免疫系统以及脊髓和脑之间流动的信号。
The concern is not so much the fleeting nastiness of mosquito bites and poison ivy, but the unending misery caused by chronic itching — the kind that won't go away, that torments people night and day and very often resists remedies like antihistamines and cortisone cream.
研究所关注的重点并非是像蚊虫叮咬和毒葛那种转瞬即逝的小麻烦，而是因长期慢性瘙痒引起的无休止的痛苦——它挥之不去，日日夜夜折磨着人们，而且往往对抗组胺药物和可的松软膏等疗法都具有耐受性。
For the first time in the United States, itching research and treatment centers have opened: Temple's in September, in Philadelphia, and Washington University's Center for the Study of Itch, in 2011, in St. Louis.
9月在费城开办的天普大学瘙痒中心以及2011年在圣路易斯开办的华盛顿大学(Washington University)瘙痒研究中心(Center for the Study of Itch)是美国开办的第一批瘙痒研究和治疗中心。
"Itch is now where pain was probably 20 years ago," said Dr. Lynn Cornelius, chief of the dermatology division at Washington University School of Medicine. "It used to be lumped together with pain."
“今天，人们对瘙痒的重视程度与20年前对疼痛的重视程度相仿，”华盛顿大学医学院(Washington University School of Medicine)皮肤病学系的主任琳内特·科尔内留斯(Lynn Cornelius)博士说。“过去，人们总是把它与疼痛混为一谈。”
But now, she said, there is more interest in itching and in sorting out its different types, and more research money being spent on it.
但现在，她继续说，人们对瘙痒及其分类更感兴趣，也愿意在这方面投入大笔的研究资金。
"The science has to lead to treatment, I believe," Dr. Cornelius said. "If that happens, it will translate to better and better, more targeted therapies, so clinicians won't just look upon someone itching as someone who needs antihistamines."
“我坚信，科学的发展必将导致治疗领域的进步，”科尔内留斯博士说。“若果真有这么一天，科研成果将转化为更好，也更有针对性的疗法，这样，医生就不至于只能向受到瘙痒困扰的患者处方抗组胺药物了。”
Scratching, and therefore itching, appear widespread in the animal kingdom — though no one knows for sure why animals claw, bite or peck themselves, or scrape against trees or fences.
搔痒行为在动物世界里普遍存在。尽管没有人能确切地知道动物为什么要去抓、咬或啄自己，或将身体在树木或栅栏上摩擦，但人们推测，这很可能是因为它们也会感到瘙痒。
Even fruit flies engage in "robust grooming behaviors" that look a lot like scratching when they are infected with mites, said Diana Bautista, an assistant professor of cell and developmental biology at the University of California, Berkeley. Her research includes studying various strains of itchy mice that are models for human ailments.
即使是果蝇这种低等生物，在它们感染螨虫时，也会出现一种跟搔痒看起来颇为相似的“强力梳理行为(robust grooming behaviors)”，加州大学伯克利分校(University of California, Berkeley)的细胞和发育生物学助理教授戴安娜·鲍蒂斯塔(Diana Bautista)说。此外，她的研究还包括多种品系的瘙痒小鼠，它们都是业已建立的不同人类疾病的模型小鼠。
"I have a collection of movies showing different animals scratching," Dr. Bautista said. "I'm hoping they will help me determine if there is a difference between itch-evoked scratching versus wiping and other behaviors in diverse species."
“我还收集了许多介绍不同动物搔痒行为的视频资料，”鲍蒂斯塔博士说，“我希望它们可以帮助我确定在不同的物种中，瘙痒引起的挠痒行为与擦拭及其他行为之间是否存在差异。”
One of her favorite videos shows a seal lying on the beach, briskly rubbing its head with a flipper.
她最喜欢的一段视频展示了这样的景象：一只海豹躺在沙滩上，轻快地用自己的鳍状肢摩擦着头部。
In people, there are different types of itching. The most familiar type, from a mosquito bite or hives, occurs when cells in the skin release histamine, which causes nerves in the skin to fire off signals to the spinal cord and brain. Antihistamine pills or creams usually bring relief.
在人类当中，存在着多种不同类型的瘙痒。人们最熟悉的一种因蚊虫叮咬或荨麻疹引起，此时皮肤细胞释放出组胺，引起皮肤中的神经产生信号，并传导到脊髓和大脑。抗组胺片剂或药膏通常可以缓解其症状。
But antihistamines are often no help to people with chronic itching, which can be caused by skin diseases like eczema or psoriasis, kidney or liver failure, dry skin, an overactive thyroid gland, certain cancers, and pinched or damaged nerves. And the itching from psoriasis almost certainly has a different mechanism from that caused by a pinched nerve.
然而，这些药物对慢性瘙痒患者往往就爱莫能助了。湿疹或银屑病（牛皮癣）等皮肤病、肾脏或肝脏衰竭、皮肤干燥、甲状腺功能亢进、某些癌症以及神经受到挤压或损坏都可能导致慢性瘙痒。而且几乎可以肯定的是，因银屑病引起的瘙痒与神经受压引起的瘙痒具有不同的机制。
"It's a very hot area," Dr. Cornelius said. "It's a huge clinical problem and a huge unmet market."
“这是一个非常热门的领域，”科尔内留斯博士说，“它既是重大的临床问题，又提供了一个需求远远未得到满足的巨大市场。”
Recent research has shown that substances other than histamine, released from inflammatory cells, are involved in chronic itching, along with three different types of nerve cells, Dr. Bautista said. Drug companies are trying to find ways to block those substances.
鲍蒂斯塔博士介绍道，最近的研究表明，除了组胺，炎性细胞还释放出了其他一些与慢性瘙痒有关的物质，此外，还有三种不同类型的神经细胞也参与了这一过程。制药公司正致力于寻找可阻断这些物质的方法。
"Before, the focus was on next-generation antihistamines," Dr. Bautista said. "Now, it's on new molecular and cellular targets to develop new therapies. The pharmaceutical industry is recognizing that they have to go beyond antihistamines."
“以前，他们的研发重点一直是新一代的抗组胺药物，”鲍蒂斯塔博士说，“现在，他们则瞄准了新的分子和细胞靶标来开发新的疗法。医药行业已经认识到，他们不能再局限于抗组胺药物，必须有所超越。”
But pain pathways have to be dissected in minute detail if new targets are to be found. Many researchers say that one of the most important advances in the field was reported in the journal Nature in 2007 by a Washington University team led by Zhou-Feng Chen, who is now director of the itch center. Working with mice, his team was studying receptors, molecules on cells that respond to certain chemical signals to change the cells' behavior.
但是，要找到新的靶标，就必须将疼痛通路的每个微小的细节都剖析清楚。现任华盛顿大学瘙痒中心主任陈宙峰(Zhou-Feng Chen)领导团队利用小鼠研究了可对特定的化学信号作出反应，并改变细胞行为的细胞表面受体和分子。这一2007年发表在《自然》杂志(Nature)上的研究被众多研究人员一致认为是该领域最重要的进展之一。
The group was the first to find a receptor in the spinal cord that was specific for itching, called gastrin-releasing peptide receptor, or GRPR. The discovery helped to prove that signals for itching and pain travel on different pathways.
该小组首次在脊髓中发现了瘙痒特异性受体，称为胃泌素释放肽受体(gastrin-releasing peptide receptor)，简称GRPR。这一发现有助于证明瘙痒和疼痛的信号传导途径并不相同。
In an interview, Dr. Chen said that mice without the receptor — or with the receptor blocked by a drug — did not itch. Nor was the group without a receptor harmed by the lack of it.
陈博士在接受采访时表示，不具备该受体，或该受体被药物阻断的小鼠就不会产生瘙痒的感觉。且无受体组的小鼠并未因此而受到损害。
"If you block function of this receptor alone, you pretty much stop chronic itching," he said.
“仅仅阻断该受体的功能，就几乎足以给慢性瘙痒画上句号，”他说。
The receptor is present in humans, too, and Dr. Chen said it might be possible to develop a drug that would block it.
该受体也存在于人体之中，陈博士认为未来有望开发出一种可以阻断它的药物。
For many patients, new treatments cannot come soon enough.
但对于大多数患者而言，新疗法问世的速度还不够快。
Chronic itching becomes more common with age. One reason is that older people often develop dry skin, but Dr. Yosipovitch said the itching also might occur because certain nerves in the skin deteriorate — nerves that transmit pain and inhibit itching. "Then itch kind of pops out," he said.
随着年龄的增长，慢性瘙痒在人群中日渐常见。其原因之一是老年人往往存在皮肤干燥。但杨斯波维奇博士认为，皮肤中某些神经的受损也可能造成瘙痒——这些神经原本负责传导疼痛并抑制瘙痒，它们一出毛病，“瘙痒就蹦了出来，”他说。
Aging monkeys have provided some clues. When Dr. Yosipovitch was still at Wake Forest, he and his colleagues noticed older female macaques scratching their backs and lower limbs, the same spots where older people tend to itch.
衰老的猴子为此提供了一些线索。早在杨斯波维奇博士在维克森林大学工作时，他和同事们就发现老年雌性猕猴会抓挠自己的背部和下肢——老年人经常感到瘙痒的也是同样的部位。
They sent samples from the monkeys to Dr. Chen, who found extra activity in the skin and spinal cord from the gene that produces GRPR, the itch receptor. Why the gene becomes more active with aging is not known, but this finding in a primate supports the idea that the receptor is a good target for new drugs in people, Dr. Chen said.
他们将这些猴子的样本送到了陈博士的实验室。陈博士他们随后发现，在这些猴子的皮肤和脊髓里，表达瘙痒受体GRPR的基因过度活跃。陈博士表示，目前尚不清楚该基因为什么会随着衰老而趋于活跃，但这一在灵长类身上得到的发现支持这一观点：该受体是研发治疗人类瘙痒的新药的良好靶标。
Many older people have trouble with itching in hard-to-reach spots on the back, between or just below the shoulder blades.
许多老年人都存在这样的麻烦：瘙痒的部位正好位于后背上肩胛骨下方或其之间的位置，他们的手很难够着。
"It drives them crazy," said Dr. Cornelius, at Washington University. They rub against door jambs, stockpile back scratchers, and enlist others to scratch them.
“这简直要把他们逼疯了，”科尼利厄斯博士在华盛顿大学时说。他们只好用身体摩擦门框，大量购置痒痒挠，并要求其他人来帮他们瘙痒。
The condition has a name, notalgia paresthetica, and is often associated with spine and disk problems that pinch or damage nerves. The skin in the itchy spots may darken.
这种疾病名为感觉异常性背痛(notalgia paresthetica)，它通常与脊柱和椎间盘出现问题，压迫或损伤了神经相关。痒点处的肤色有可能会变暗。
"Some neurologists, I would say the majority, do not know about this," Dr. Yosipovitch said.
“一部分神经科医生，甚至可以说其中的大多数都不知道这一点，”杨斯波维奇博士说。
He and other doctors have prescribed various remedies — numbing patches, sometimes along with the hot-pepper ingredient capsaicin; Botox injections; pills like gabapentin that affect nerve transmission; and physical therapy to change posture. Often, it is possible to find something that helps.
他和其他医生也曾处方过多种治疗方法：止痒贴片，有时辅以辣椒中的成分辣椒素；注射肉毒杆菌毒素(Botox)；加巴喷丁(gabapentin)等可影响神经传导的药剂；物理治疗等，试图改善瘙痒症状。但基本上没有一种见效。
Dr. Yosipovitch said many patients found their way to him only after seeing multiple doctors who could not help and who sometimes misdiagnosed their problems as mental rather than physical.
杨斯波维奇博士说，许多患者都是在拜访过众多表示爱莫能助的医生（其中甚至有人将身体的瘙痒误诊为心理疾病）后才找上了自己。
"They're not crazy," he said.
“他们当然不是脑筋出了问题，”他说。
One of the patients was a boy who had scratched his arms and legs raw. Unable to find a cause or a treatment that worked, doctors had referred him and his family to a psychiatrist.
其中一名患者是个男孩子，他把自己的手臂和腿都抓挠得破了皮。医生找不到病因，也没什么有效的疗法，只好将他转诊给了心理医生。
In an interview, the patient, Joshua Riegel, now 18, said, "They said I was doing it to manipulate my parents." Thus began what he calls "that weird part of my life where they thought I was mentally ill."
这位名叫乔舒亚·里格尔(Joshua Riegel)的患者现年18岁，他在接受采访时说：“他们都说我这样是故意的，目的是为了作弄我的父母。”从那时候起，他称其为“我被当成精神病的一段最诡异的人生经历”开始了。
He was 12 or 13 when the psychiatrist prescribed antidepressants, which he dutifully took for two or three years. But they brought on terrible side effects: At one point he was hospitalized with suicidal thoughts.
在他十二三岁的时候，心理医生一直给他处方抗抑郁药物，他听话地坚持服用了两三年。可这些药物带来了可怕的副作用：他一度因为自杀念头而不得不住院。
As a last resort, his parents took him from their home in Hillsville, Va., to see Dr. Yosipovitch, who was then at Wake Forest.
抱着最后一丝希望，他的父母带他离开了位于弗吉尼亚州希尔斯维尔的家，来到维克森林大学拜访当时在那里工作的杨斯波维奇博士。
"He had a hunch on what it was," Mr. Riegel said.
“他好像凭直觉就知道是哪里不对劲，”里格尔先生说。
Tests found a rare form of a genetic disease, epidermolysis bullosa, that was causing a particularly destructive set of symptoms: intense itching and skin so fragile that scratching ripped it to shreds.
经过测试，研究人员发现他患有一种很罕见的遗传病——大疱性表皮松解症(epidermolysis bullosa)，这种病可以造成一系列极具破坏性的症状：剧烈瘙痒，皮肤极度脆弱，以至于连挠痒都会将皮肤划破。
"Dr. Yosipovitch was quite angry I was being told I was mentally ill when I wasn't," Mr. Riegel recalled.
“在得知明明没有精神病的我却被人说成是精神病时，杨斯波维奇博士非常生气，”里格尔先生回忆道。
Getting off the antidepressants lifted his spirits and let him be normal again. Since then, other drugs have been prescribed for the itching, with mixed results. It never really goes away, but Mr. Riegel uses video games or his cellphone to take his mind off it and keep from scratching.
停用抗抑郁药物后，他的精神重新振奋起来，并恢复了正常。此后，医生向他处方了其他药物来治疗瘙痒，效果好坏参半。虽然从未真正摆脱过瘙痒，但里格尔先生可以借助电脑游戏或手机转移自己的注意力，以避免抓伤自己。
For people with other types of chronic itching, Dr. Yosipovitch said: "This is just the beginning of a big era. In the next five years I predict there will be drugs targeted specifically for itch. We're in the middle of the tip of an iceberg."
对于患有其他类型慢性瘙痒的患者而言，杨斯波维奇博士说：“这个伟大的时代才刚刚拉开序幕。预计在接下来的五年里就会出现专门针对瘙痒的靶向药物。我们正站在冰山的一角上。”