세균배양에 필요한 배지는 배양하고자하는 미생물의 종류에 따라 적합한 것을 선택하여 사용하여야 한다. 따라서 미생물의 종류에 따라 배지의 제법이 다소 달라질 수 있다. 여기서는 배지를 준비할 때 기본적인 주의점과 멸균법 및 평판배지, 사면배지 준비법을 살펴보고, 세균배양에 가장 많이 쓰이는 영양배지의 제법을 실습하도록 한다.
1) 배양배지의 준비
배지를 만들 때는 그 조성에 따라 필요한 내용물을 저울 등으로 담아 용기에 담고 혼합하여 물을 가한 후 멸균하는데, 세균배양에 필요한 다양한 배지들이 조성대로 이미 만들어져 탈수시킨 상태(dehydracted media)로 시판되는 종류도 많다. 탈수배지는 정해진 농도로 물을 가한 후, 멸균하여 사용하면 된다. 일반적으로 배지를 만들 때는 다음 사항을 지켜야 한다.
① 배지를 담을 유리용기는 가능하면 깨끗한 것으로 경질유리제품 (pyrex)을 이용한다. ② 특별히 언급한 경우가 아니면 증류수를 사용한다.
③ 배지 내용물을 정확히 달아 언급한 순서대로 첨가한다.
배지의 pH는 미생물의 생장 에 의해 변화된다. 따라서 필요할 경우 배지 준비시 pH측정기나 pH 지시종이로 재고 지정한대로 배지의 pH를 맟추도록 한다. 대개의 배지는 그 구성성분이 완충능을 갖도록 되어있으나, 필요한 경우 제조시 산이나 알칼리를 첨가하여 pH를 보정해 주어야 한다.
④ 물에 녹인 배지는 특별히 불용성 물질이 함유된 경우를 제외하고는 맑아야하며, 배지 가 맑아야만 접종 후 균체의 생장여부를 쉽게 판독할 수 있다. 따라서, 배지를 맑게 하기 위해서는 여과지 등으로 직접 여과시키거나, 계란의 흰자(egg white)를 가한 후 가열하면 녹지 않은 입자들이 계란 흰자와 함께 응어리로 뭉쳐지는데, 이를 여과하여 맑게 만들기도 한다. 여과시 배지의 양이 적은 것은 여과지로 (Whatman No. 1) 거르 고, 양이 많을 경우에는 두꺼운 펼프층이나, 목화솜 등을 Buchner funnel에 진공펌프 를 이용하여 여과시키도록 한다. 이런 연후에 구멍크기가 작은 여과지로 걸러 모든 현탁입자를 제거시킨다.
⑤ 배양배지는 멸균 전에 사용하기 편리한 양만큼 솜마개, 금속마개 또는 나선형 뚜껑이 덮힌 시험관이나 플라스크에 나누어 담는다.
2) 배지 멸균시의 일반적인 유의사항
배지는 일반적으로 고압증기멸균기(autoclave)를 사용하여 121℃(101.3kpa 또는 15 p.s.i)에서 15분정도 멸균하나 멸균시간은 용기의 종류나 배지의 양에 따라 다르다. 멸균시간은 정확히 측정하여 결정하도록 한다. 왜냐하면 너무 가열되면 대부분의 배지성분이 손상되기 때문이다. 또한 배지 멸균시 솜마게는 종이나 알루미늄 박으로 싸서 너무 젖지 않도록 하고, 나선형 뚜껑등은 약간 느슨하게 닫아서 가열에 의한 팽창 때문에 깨지지 않도록 하고, 멸균후에 꺼내어 꽉 잠그도록 한다.
열에 약한 배지 (또는 배지 성분)는 여과하거나 변형된 열처리법으로 멸균하되 초기에 배지를 만들 때 오염되지 않도록 무균조작에 신경쓰도록 한다. 주로 열에 약한 성분은 여과하고, 열에 안정한 성분은 별도로 습윤멸균한 후 무균적으로 둘을 섞어 사용한다.
3) 탄수화물의 멸균과정
일반적으로 가능하면 고농도의 용액을 여과하여 사용한다. 탄수화물의 종류에 따라 다음의 방법으로도 멸균가능하다.
① Tydalization : 하루간격으로 3일동안 100℃에서 30분간 끓인다. 주로 adonitol, arabinose, inositol, raffinose, rhamnose, sorbitol, trehalose.
② 35kpa(약 5.2 p.s.i)에서 25분간 습윤멸균 : aesculin, fructose, glucose, glycerol, lactose, mannitol, salicin, sucrose 등
③ 여과법으로만 사용할 것 : inulin, maltose, xylose.
열에 안정한 배지성분은 모두 물에 녹여 따로 습윤멸균한 후, 위와 같이 따로 멸균한 탄수화물을 무균적으로 첨가한다. 이 경우 곧바로 사용하지 말고 37℃에서 하루밤 방치하여 멸균여부를 확인한후 사용하도록 하고, 특정당의 이용하는데 사용하고자 할 때는 그 배지에서 확실히 생장하는 것으로 알려진 표준 균주를 배양했을 대 양성반응이 나타나는지 확인한 후에 사용하도록 함이 현명하다.
④ 보관법 : 나선뚜껑 시험관에 든 배지는 직사광선을 피하여 상온에서 보관한다. 이 용기는 배지의 증발을 방지하여 보관시 배지의 건조를 방지하는 이점이 있다. 솜마개 또는 금속마개를 한 시험관이나 플라스크는 4℃에 보관하도록 한다.
4) 고체 평판 및 사면배지의 준비법
고체배지는 다량준비하여 멸균하고 (미리 멸균하여 둔 것은 사용직전에 고압증기 처리하거나 끓여서 녹이고) 50℃로 식힌 후, 열에 약한 혈액, 항생제, 당, 아미노산등은 역시 45℃정도로 맞추어 첨가하되 거품이 일지 않도록 용기를 조심스럽게 흔들어 혼합한다. 그런 다음 멸균된 페트리 접시나 용기에 나누어 붓는다.
① 페트리접시에 붓는 법 : 멸균된 페트리 접시를 바닥이 평평한 곳에 준비해 두고 45～50℃로 식힌 배지가 든 플라스크의 입구를 불꽃으로 살균한 다음, 페트리접시의 뚜껑을 열고 15㎖ 정도씩 붓는다. 이때 오염이 되지 않도록 주의하고 배지를 부은 페트리접시는 배지가 굳을 때까지 움직이지 않도록 한다. 굳은 고체 평판배지는 비닐막 등으로 잘 싸서 4℃에 보관하도록 하며, 사용 전에 잘 말려서 사용하도록 한다. 한천배지의 표면에 물기가 있으면 콜로니가 명확히 구분되지 않게 되어 단일 콜로니의 선별이 어렵다. 4℃에서 며칠간 보관한 경우는 건조시간이 단축되거나, 따로 건조시킬 필요가 없는데, 필요할 경우 37℃에서 하룻밤 방치하여 배지를 말리도록 한다. 이 과정은 건조와 동시에 배지의 오염여부를 확인할 수 있는 장점이 있다.
② 사면배지 준비법 : 물에 녹인 배지를 중탕하여 잘 녹인 후 약 5㎖씩 (시험관의 크기에 따라 양을 조절한다) 나누어 담고 마개한 후, 습윤멸균한다. 멸균이 끝난 후 배지를 비스듬히 기울여(30-40도 정도) 굳힌다. 이 때 사면배지가 너무 경사지거나 배지량이 많아서 시험관 입구 가까이에 도달하지 않도록 주의한다. 대개 시험관의 ½정도로 한다. 필요에 따라 접종침을 찔러 접종할 경우에는 약 7㎖의 배지를 붓고 바로 세워서 굳히도록 한다. 사면배지 역시 4℃에서 보관하도록 한다.
2. 실험 재료 및 방법
▣ 재 료
한천(agar), 효모추출물(yeast extract), tryptone, NaCl,
2ℓ짜리 삼각플라스크 혹은 비이커,
500㎖짜리 삼각플라스크, 500㎖짜리 눈금 실린더,
솜, 마개,
pH측정기, 저울, 1N HCl, 1N NaOH, 멸균기
시약용 숟갈, 유산지, 증류수가 들어 있는 비이커 (또는 세척병)
▣ 과 정
① 2ℓ플라스크에 증류수 500㎖을 붓는다.
② tryptone 10g, yeast extract 5g, NaCl 10g 을 플라스크에 달아 넣는다. 이때 유산지 를 천칭위에 올려놓고, 증류수로 잘 씻은 시약용 숟갈을 휴지로 닦아 물기를 완전히 제거하여, 시약을 달도록 한다. 한 시약을 달고 난 후 에는 숟갈을 꼭 세척하도록 하 며, 부주의하여 시약통의 시약이 다른 시약에 의해 오염되지 않도록 주의한다. 또한 천칭에 시약을 흘리지 않도록 주의하며, 흘린 경우에는 즉시 닦아내도록 한다.
③ 플라스크를 잘 흔들어 내용물을 다 녹인다. 증류수를 가하여 전체량이 1ℓ가 되도록 한다.
④ 위 용액을 500㎖ 플라스크에 250㎖씩 나누어 담고 다음과 같이 한다. 첫 번째 배지에는 더 이상 배지성분을 첨가하지 않고 액체배지로 사용하고, 두 번째 배지에는 한천 3.75g (고체배지를 만들 때는 한천을 배지 1 리터당 15g을 첨가)을 가하고 흔들 어준 다음, 5분쯤후에 중탕하여 녹이되, 가끔 흔들어 준다. 이렇게 만든 것이 영양한 천배지이다.
⑤ 위의 네 가지 배지를 pH측정기(또는 pH 측정용종이)로 1N HCl이나 1N NaOH를 가 하여 pH 7.0 으로 맞춘다. 사용 후 pH 전극(electrode)은 잘 세척한다.
⑥ 시험관에 각각 나누어 담고 마개를 한 후 습윤멸균을 121℃(15 p.s.i)에서 15～20분 멸균한다.
⑦ 멸균이 끝나면 사면배지 만들어 놓은 것은 기울여 눕혀 사면배지를 만들고, 식혀서 4℃에 보관한다.
3. 실험수행상 주의 할 점
영양배지 등 영양소가 풍부한 배지에 포도당을 첨가할 때는 일반적으로 다른 배지성분과 함께 녹여 습윤멸균 하기도하며, 멸균시간을 10분 내외로 단축하기도 한다. 그러나 생장율 측정또는 생리적 특성 조사용 배지를 만들 때는 앞서 살펴본 바와 같이 여과하여 멸균한 높은 농도의 포도당 저장용액을 만들어두고 50℃정도로 식힌 배지에 첨가하도록 한다.
[éinʃənt] 1. ancient 오랜 옛날에 있었던 또는 시작된. 2. antiquated 구식이라 쓸모없게 된 ◇ antiquated system 구식이 된 제도. 3. antique 오래되어 진기한 ◇ antique chair 옛날 의자. 4. old-fashioned 시대에 뒤진, 구태의연한, 유행에 뒤진
-Zanjani'ssheepisthelatestcontributiontothecontroversialfieldofinterspeciescloning./Ininterspecific hybridisations, however, theinheritanceof plastids appears to bemoreerratic.
im·plantvt. [의학] [장기·피부 등을] 이식하다; [인공 장기 등을] 끼워넣다.
vi. [생물] [배(胚)·수정란이] (자궁에) 착상하다.
pay a visit to ..[사람·물건을] 찾아가다, 들르다(※뚜렷한 목적으로 잠깐 방문시) seem […에게] (…처럼) 보이다, 생각되다, (…)인 듯하다[to ‥]
It's difficult to imagine that 10,000 years ago, right here in North America, there lived giant animals that are now the stuff of legends - mammoths and mastodons, ground sloths and saber-tooth cats. They, and thousands of other species, have vanished from the Earth. Today, partly due to the expansion of one species - ours - animals are going extinct faster than ever before.
The very definition of extinct means forever, but what if that didn't have to be? As Lesley Stahl reported in early 2010, scientists are making remarkable advances that are bringing us closer than ever before to the possibility of a true animal resurrection.
Who wouldn't be dazzled by an animal like the woolly mammoth, or the sabretooth tiger, the Irish elk or the giant sloth? Today they exist just as bones in museums, alive only in our imaginations and the recreations of artists and filmmakers. But what if that could change?
In the age of DNA, we now know that these vanished creatures, like all life on Earth, are ultimately nothing more than sequences of the four letters - A, C, T, and G - that make up the genetic blueprint or code of life. The codes for extinct animals were thought to have died along with them, until recently, when machines like one at the Smithsonian's DNA lab started working magic.
"Just the study of ancient DNA only broke onto the scene 20 years ago or so. The idea that we could harvest DNA from extinct creatures, from fossil bones, learn something about the past," Sean Carroll, a professor of molecular biology and genetics at the University of Wisconsin, told Stahl.
Carroll says that like so many things in the field of DNA, the progress has been staggering.
One surprising discovery has been the value of ancient hair. Scientists recently discovered that the hair shaft seals DNA inside it like a biological plastic, protecting it, and making hair a rich and plentiful source of genetic information.
"Does that mean that you can take extinct animals, I mean, there's hair in museums? ...And get the genetic sequencing?" Stahl asked.
"Possibly, and especially if those animals were preserved in any way, there's a good prospect of that. It's sort of like 'CSI,' you know? How good is this forensic material? Can you get good DNA information from older and older and older material? That's pretty promising," Carroll replied.
Dusty old specimens that have been tucked away in the drawers of natural history museums like the Smithsonian are suddenly potential treasure troves of genetic information: just a couple of years ago, using only a few clumps of wooly mammoth hair, scientists at Penn State were able to extract enough DNA fragments to figure out most of its genetic sequence, making the woolly mammoth the first extinct animal to have its genome decoded - which raises the question of whether resurrecting one of these creatures is really possible.
Scientists say one option would be genetic engineering: take a living animal that's related to the mammoth, like the elephant, figure out all the places where its DNA differs from the mammoth's, and then alter the elephant's DNA to make it match.
That's not possible just yet, but there may be another way: cloning.
"Is it possible that we're gonna get the full DNA of the woolly mammoth and be able to clone it?" Stahl asked.
"Yes, I think we'll be able to get much, if not all, of the woolly mammoth DNA. And the great advantage there is that a lot of the specimens are in permafrost. So they're sorta been conveniently frozen for us, which preserves DNA, preserves tissue better," Carroll said.
But for cloning, just knowing the DNA sequence from hair isn't enough. You'd need an intact mammoth cell, which Carroll says will be difficult to find, but not impossible.
"It could be a skin cell. It could be any particular cell that hopefully has been preserved well enough, stayed frozen for thousands of years and to transfer the nucleus of that cell into, for example an egg of an elephant," Carroll explained.
He told Stahl that the two species are "close enough" that maybe the elephant could serve as a surrogate mother.
It's called interspecies cloning: implanting DNA from one species into the eggs of another.
Anyone who wants to try it, with a mammoth or anything else, would be well-served to pay a visit to Dr. Betsy Dresser in New Orleans.
Tucked away on 1,200 acres of land that seem part Serengeti, part high-tech medical facility, she and her staff at the Audubon Nature Institute have been working quietly for years on the science and the art of interspecies cloning, and she'll be the first to tell you that, even with living animals, it isn't easy.
"You don't just clone some cells and then all of a sudden you have a baby. I mean, there's so many scientific steps along the way, knowing everything from hormones to the proper surrogate to, you know, length of pregnancy," she explained. "Because, see, we don't know how long a woolly mammoth, the gestation period. We can guess, but we don't know, really."
But Dr. Dresser's work on interspecies cloning is focused on the future, not the past. Rather than trying to resurrect extinct creatures, her goal is to keep the animals we have today from going extinct tomorrow.
"I feel like we're in the emergency room of the wildlife business, really," she told Stahl. "I don't want to see elephants in textbooks or, you know, the way we see dinosaurs. We're going to lose a lot of species if we don't do somethin' about it."
Dresser and her team are trying to increase the populations of endangered animals by putting their DNA into the eggs of their non-endangered relatives.
On the day we visited, they were laparoscopically removing eggs from an ordinary housecat, then sending the eggs down the hall to have the housecat DNA literally sucked out of them.
"What she's doing is she's removing the DNA from this domestic cat egg. And she can see it by what we call fluorescing it," Dresser explained, while observing the procedure with Stahl. "It becomes just very blue, and so now she knows where it is. And now you'll see her go in there and be able to remove it."
Once the housecat DNA is deposited outside of the egg, they will replace it with the DNA of an endangered Arabian sandcat, a completely different species, gathered from a tiny piece of skin.
"And there you see it being inserted into the domestic cat egg," Dresser explained.
"And you made that from just skin?" Stahl asked.
"Just from skin cells, right," Dresser said.
An electrical pulse starts the egg dividing, and if all goes as planned, the now sandcat embryo will be put back into the domestic cat to grow to term.
It has worked before -- with African wildcats; the research has resulted in some interspecies offspring. These interspecies clones were so normal that they even mated the old-fashioned way and produced kittens.
"Eight kittens altogether. We had a couple litters," Dresser told Stahl. "Totally African wildcats, totally healthy. And it said to us, 'Hey this works.' And now that we know we can do it, we can say to the world, 'These animals do develop. They do reproduce naturally.' And we can use this as a tool for endangered species."
Extra: The Tasmanian Tiger
And Dresser is working her way up. Her next interspecies cloning project will use the non-endangered caracal cat as a surrogate mother for an endangered lynx; and after that, the Eland antelope as a surrogate for its endangered cousin, the bongo.
"You know, there are still people who get nervous at the idea of cloning. They think there's something wrong about it," Stahl remarked.
"I'll tell you what, if you have to choose cloning or extinction, I'm gonna choose cloning. But I wanna be darn sure that I know how to do it. And if we don't do it while we have the animals now to be able to learn how to do it, then we're not gonna have a choice. It's not gonna be an option," Dresser said.
So to keep her options open while she's mastering interspecies cloning, she's also putting as many animals as she can on ice, literally.
Dresser is the keeper of a new kind of zoo - a frozen zoo - where she's collecting tiny skin samples from thousands of different animals, representing hundreds of species, and is storing them at 343 degrees below zero in tiny canisters inside tanks filled with liquid nitrogen.
"We've got lions and tigers, we've got gorillas and rhinos. We've got little frogs. All of the animals...that people know in zoos," she explained.
Extra: Frozen Zoo
Asked how long a piece of skin can be viable, Dresser said, "We think these cells can sit here for hundreds, maybe thousands of years."
"So, if any one of these animals were to go extinct, you could bring them back?" Stahl asked.
"In theory, I believe we can," Dresser said.
And she agreed that her frozen zoo is kind of Noah's Ark.
"Do you think we're at the stage where we should be taking every single wild animal, even if they're not endangered, and putting them in a frozen zoo?" Stahl asked.
"Yes. I absolutely do," Dresser said. "What have we got to lose? I think we should put every species in that we can, while we have the opportunity."
Which raises the question: with so many living animals today threatened, why think about resurrecting extinct ones, like the mammoth?
"To bring the woolly mammoth back, we don't have enough space for the big animals we already have," Stahl told Sean Carroll.
"These projects, like the woolly mammoth, they inspire people to think about the meaning of what we're doing here. And why would you invest years and years of your life in trying to bring back a woolly mammoth or taking care of them if you did," he replied.
"That's an excellent question," Stahl said.
"I think it would fire up people's imaginations. And I think somewhere there's a 9-year-old girl watching this program and listening to this saying, 'That's what I wanna do. I wanna bring back these creatures that are extinct. Or I wanna protect creatures that are now threatened from going extinct.' So in many ways, I think the woolly mammoth can sort of be a poster animal for a general effort of being more conscious of our activities on the planet," Carroll explained.
No one has yet found the intact cell it would take to resurrect that poster animal, but in Siberia, four years ago, a reindeer herder discovered a remarkably well-preserved one month old baby mammoth that had lain frozen in permafrost for 40,000 years.
Its DNA was in better shape than any previously found, raising hopes that between new finds and new technology, it may just be a matter of time.
Betsy Dresser stepped down as director of the Audubon Nature Institute recently to work on a book about endangered species and new technology. She continues to consult on the center's work, which is ongoing.
No one knows what causes lifelong face blindness. It was discovered so recently, scientists are just beginning to unravel its secrets. And some of the clues are coming from people who once had normal face recognition, but lost it after suffering damage to part of the brain. And in an interesting twist, those people are also offering insight into the way the rest of us recognize faces. Imagine waking up after a trauma and not being able to recognize the people closest to you -- that's what happened to Colleen Castaldo.
Lesley Stahl: Up until the fall of 2009, did you have any trouble recognizing faces at all?
Colleen Castaldo: No, not at all.
Lesley Stahl: Just like everybody else?
Colleen Castaldo: Like everybody else, yeah.
That all changed late one night when Colleen had a seizure and was rushed to the hospital. Her doctors found a brain tumor and did surgery to remove it, but as she recovered, she started noticing that something wasn't right.
Colleen Castaldo: The nurses. I thought that I was meeting them each for the first time. And then, I would, you know, listen to them and think, I don't know, they were acting like they knew me already.
Lesley Stahl: Oh, disorienting.
She figured it was the medication, until her close friend Doreen came to visit wearing white, and Colleen assumed she was part of the medical staff.
Colleen Castaldo: I looked at her, I smiled and I turned back to my husband and started to talk to him, and he stood up and said, "Doreen." And I looked and thought, "Doreen?" And then, it hit me. I knew right then and there, this is the problem I had been having, that I--
Lesley Stahl: Faces.
Colleen Castaldo: I just-- yeah, faces.
Now even faces she knew well before...
Colleen Castaldo: [George Clooney] No.
Lesley Stahl: OK, well that's George Clooney.
Colleen Castaldo: Oh, wow. No, I wouldn't know that.
...are a mystery to her.
Colleen Castaldo: No, I don't know who that is. Who is it?
Lesley Stahl: The president.
Brad Duchaine showed me an MRI scan of Colleen's brain.
Lesley Stahl: Is that a hole in her brain?
Brad Duchaine: That's right. It's in the right temporal lobe.
Lesley Stahl: So back here.
Brad Duchaine That's right.
And the location of that hole where the tumor had been was a clue. If removing that area caused the loss of face recognition, could that be where all our brains process faces? It turns out that neuroscientists have been trying to figure out how it is that our brains recognize faces for decades.
Nancy Kanwisher: Face recognition is a very difficult problem, because all faces are basically the same.
MIT neuroscientist Nancy Kanwisher...
Nancy Kanwisher: There are these two roundish things here. There's this thing there. There's this thing there. They're all the same. And so discriminating one face from another is a very computationally difficult thing, because it's those subtle differences in the same basic structure that distinguish one thing from another.
And it is exactly those subtle differences face blind people like Jo Livingston miss.
Jo Livingston: I could describe anything I can put into words. Eye color, general overall shape, whether your ears stick out. But those things would bring it down perhaps from the population of the world to a few million.
So she could say this person has dark eyes, high cheekbones, an oval face, which would allow Jo to distinguish her from this person, but this face and this face? Impossible.
Jo Livingston: I can say what I can see. But I cannot say the micro-measurements that are what tell a normal person that it's you and not somebody of the same specification.
But how is it that the rest of us can perceive these two people as distinct individuals despite the similarities? An important clue comes from what we can't distinguish: as we saw earlier, faces upside down. Like these two Duchaine showed me, which look very similar.
Brad Duchaine: Maybe you don't even see that there's any difference.
Lesley Stahl: I see something different in the lower lip.
Brad Duchaine: Yeah.
Lesley Stahl: Eyes are a little different.
Brad Duchaine: But then, if I show them to you upright, so here's the one that you saw on the left there. Looks perfectly normal. And then--
Lesley Stahl: Oh!
Brad Duchaine: Here's the one you saw on the right, you saw upside-down.
Lesley Stahl: Oh my goodness.
The eyes and mouth in the photo on the right had been turned upside-down.
Brad Duchaine: And now the face looks really grotesque.
Lesley Stahl: Wow.
Brad Duchaine: But--
Lesley Stahl: But upside-down--
Brad Duchaine: Upside-down it's really hard to see that.
Nancy Kanwisher: If you look at a face upside-down, you're very bad at recognizing it. If you look at a word or an object or a scene, you can recognize it fine upside-down.
Lesley Stahl: So what did that tell you?
Nancy Kanwisher: It tells you that there's something very special about face recognition. It works in a very different way from recognition of everything else.
And that got Kanwisher wondering if there might be a part of the brain responsible just for seeing faces. She started putting people with normal face recognition into MRI scanners and watching what happens in their brains as they look at different images.
Lesley Stahl: This is what she's seeing?
Nancy Kanwisher: Yeah. This is what she's seeing.
Lesley Stahl: She's seeing faces.
Nancy Kanwisher: Exactly. And now she's seeing objects because we want to know not just what parts of the brain are active when you see faces, but what parts are more active when you see faces than when you see objects.
Kanwisher discovered that there was indeed a place in the brain that becomes very active when we look at faces.
Nancy Kanwisher: In every subject, boom, there was this nice, big response there. It was very exciting.
And it was right in the same area where Colleen's tumor had been. It's called the fusiform face area. So could that be what's missing in people with lifelong face blindness, like Jacob Hodes? Kanwisher put him in the scanner to find out.
Nancy Kanwisher: I really did not expect to see a fusiform face area.
Lesley Stahl: So you thought there'd be nothing there. Like as if instead of having a bullet go through it, he was just born without it.
Nancy Kanwisher: That's right. That's right.
Lesley Stahl: And?
Nancy Kanwisher: And we looked at the data and his face area was beautiful. It's textbook.
She scanned Jo, Ben and Meg as well, and they had fusiform face areas too.
Lesley Stahl: So what does that say to you?
Nancy Kanwisher: It tells us that the problem is not that this thing doesn't exist. There it is. But see, that's the fun of science. It's fun to be told you're just completely and totally wrong because now you have to go back and, you know, think anew.
And one thing she and other researchers are thinking about is a phenomenon as mystifying as face blindness -- its polar opposite - super-recognizers like Jennifer Jarett, who say they recognize almost every face they have ever seen.
Lesley Stahl: Waiters?
Jennifer Jarett: Yes.
Lesley Stahl: Salespeople?
Jennifer Jarett: Yes. Yes.
Lesley Stahl: Oh, like, of course.
Jennifer Jarett: Yes, absolutely. Yes. I'll be walking down the street and I'll see someone, and I'll think, "Oh retail." And then I'll remember, "Oh OK. That person works at-- as-- whatever store and that's where I s-- or they used to work at that store 10 years ago." And then I remember.
Lesley Stahl: 10 years ago?
Jennifer Jarett: Yes, yes.
Lesley Stahl: So they're-- it doesn't matter how far back you saw these people?
Jennifer Jarett: Yes, yes.
Lesley Stahl: So as long as you look at a person and take notice, they're in there?
Jennifer Jarett: I don't even know how to get rid of people.
Only a handful of super-recognizers have been discovered so far, and Duchaine and his colleagues had to come up with a whole new way to test them.
Brad Duchaine: So here are three faces here, which you're familiar with.
Lesley Stahl: I am?
It's called the "before they were famous test" because super-recognizers can also recognize faces as they change through time.
Brad Duchaine: Does that help at all?
Lesley Stahl: You sure I know that person?
Brad Duchaine: That's Dick Cheney.
Lesley Stahl: Oh my god. That's Dick Cheney?
He told me the top right was Richard Gere, and the bottom, Nancy Pelosi.
Lesley Stahl: Wow. Those three people have changed dramatically.
He even gave me a hint with this one: he's now an actor.
Lesley Stahl: And I'm supposed to know this actor?
Clearly, I was not a super-recognizer.
Brad Duchaine: That's George Clooney.
Lesley Stahl: Man. And these super-recognizers just know this?
Brad Duchaine: The supers are really good at recognizing these faces.
Jennifer Jarett: George Clooney.
Lesley Stahl: How could you tell that was George Clooney?
Jennifer Jarett: It just looked like George Clooney to me.
Jennifer Jarett: Oh, Prince Charles. Oh, Madonna. Michael Jordan.
Jennifer Jarett: Oh that's Kato Kaelin.
Lesley Stahl: The O.J. Simpson trial.
Lesley Stahl: Wow, you are good.
But we thought we had finally stumped her with this one. She said she only had a guess.
Jennifer Jarett: If I were to guess I would say Mike Wallace.
Lesley Stahl: That is Mike Wallace.
She recognized Mike Wallace as a 6-year-old!
Lesley Stahl: I don't even understand how you do that. I can't fathom it.
Jennifer Jarett: As people age I guess the aging process somehow in my brain just seems very sort of superficial. And, you know, as if someone gets a haircut you can still recognize them. It's still the same face to me. It's just the adult version.
So why is 60 years like a haircut to her, while face blind people can't recognize someone they just saw? A team of scientists at Harvard has begun scanning the brains of super-recognizers too, to see if they might yield any clues. The science of facial recognition is in its infancy. But new discoveries can't come fast enough for one last person we'd like you to meet --13-year-old Tim McDonough from Boston, who is severely face blind.
Lesley Stahl: Can you describe what it feels like when someone comes up? You know you're supposed to know who they are--
Tim McDonough: I usually just say, you know, "Hi, nice to see ya."
Lesley Stahl: So you sometimes pretend?
Tim McDonough: Yeah.
Lesley Stahl: You fake it?
Tim McDonough: I fake it, yeah.
[Researcher: So you think it's not your mom?
Tim McDonough: Yeah.
Researcher: OK, so that actually was your mom.]
Tim is working with the Harvard team to see if they can help him learn to recognize his mother's face. It's part of a pilot program to see if face blindness might someday be treatable. So far, it's not.
Tim McDonough: I just hope that nobody tries to talk to me because, if they do, they--
Lesley Stahl: They want to talk about something you've done with them, or something.
Tim McDonough: Yeah. And I don't know who they are.
Lesley Stahl: So it must be really hard to make friends.
Tim McDonough: It is, yeah. Takes me a while to make friends.
It turns out making friends can be tricky at both ends of the face recognition spectrum. Super-recognizers can seem like stalkers.
Jennifer Jarett: I would see someone, you know, weeks or months later at a party and people would say, "Oh, do you know each other?" And I'd say, "Yes." And the other person would say, "No." And I'd say, "No, don't you remember the first week of classes? You were walking to English class with someone..." And people would look at me really strangely and sort of uncomfortably, I think, a lot.
Jennifer says she's now learned to take her cues from others, ironically, just as face blind people do...
Jacob Hodes: I'll play this eye contact game where I'll wait. I'm not gonna really look at you, but I'll wait to see if you look at me. And then, "Oh, you look at me. Oh, look-- oh, hi."
Lesley Stahl: So you're always waiting for a cue from them?
Jacob Hodes: Yeah. So I'll hang back a little bit, which I don't wanna do.
Lesley Stahl: In any social situation, are you always a little anxious?
Oliver Sacks: I'm more than a little anxious. And I tend to keep my mouth closed before I make some awful blunder. Of course, another tactic, or strategy, is to smile at everybody.
That's what Chuck Close told us he does.
Chuck Close: You have to be really charming. If you are going to insult them by not remembering them, you just have to be extremely charming so that people don't hold this stuff against you.
Lesley Stahl: Do you feel now that you're missing out on something?
Ben Dubrovsky: Oh yeah.
Meg Novotny: Yeah.
Ben Dubrovsky: Definitely. I notice a loss.
Ben Dubrovsky: I understand someone by an abstraction. I put together a set of information that to me means mother or means Lesley.
Lesley Stahl: But it's not a visualization of a face.
Ben Dubrovsky: And the question, the thing that I wonder next, you know, is how does it affect even things like love?
Lesley Stahl: How does it?
Ben Dubrovsky: When people talk about love they say, "I carry the person with me. I carry their image with me." I don't carry their image. Does that mean I experience it differently? And how would I ever know? I don't know.
Jacob Hodes: There's a long tail of stuff that happens that you're missing. Connections you're not making.
Lesley Stahl: Still?
Jacob Hodes: Oh yeah. Yeah, yeah, yeah.
Meg Novotny: At least now we understand why.
Jacob Hodes: Yeah, right.
Meg Novotny: And it's therapeutic, but it doesn't fix it.