美国国家公共电台 NPR With No Sense Of Smell, The World Can Be A Grayer, Scarier Place（在线收听）

With No Sense Of Smell, The World Can Be A Grayer, Scarier Place 

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Let's hear about life without the sense of smell. Garbage collectors, new parents changing diapers and anyone who's ever ridden a subway might find something appealing about the condition known as anosmia - the inability to smell. But as Annette Heist reports, losing your sense of smell often means the loss of much more.

ANNETTE HEIST, BYLINE: Meet Nisha Pradhan.

Am I saying your name right?

NISHA PRADHAN: Yes.

HEIST: She's 21 years old. She just graduated from Rosemont College near Philadelphia - biology with a dual minor. And she's headed to med school.

PRADHAN: Yes, hopefully.

HEIST: Like a lot of us, Nisha loves to cook. But there's one problem. She's anosmic.

PRADHAN: For as long as I can remember, I've never been able to smell.

HEIST: And that means she can't always taste what she's made.

BEVERLY COWART: When you lose your sense of smell, your whole sense of food flavor is distorted and diminished.

HEIST: That's Beverly Cowart of the Monell Chemical Senses Center in Philadelphia.

COWART: What you're missing are the sort of subtle distinctions - the difference between strawberry and banana, between chocolate and vanilla.

HEIST: And that can make eating pretty unsatisfying for anosmics.

PRADHAN: I think a lot of us today like to pretend or be foodies. And we all like to talk about, oh, I think this could use a little bit more lemongrass or I think this has a hint of cinnamon. I can't really participate in those conversations. So I do feel some sense of loss or some sense of isolation when eating with other people.

HEIST: You need olfactory receptor neurons to smell. These nerve cells carry messages from the outside world to your brain.

COWART: What we smell is literally a piece of the thing that we smell. It's a molecule that's been given off by that thing.

HEIST: There aren't good numbers for how many people suffer from smell loss, and the causes of it vary. Some people are born with no sense of smell. That's called congenital anosmia, a rare condition. Acquired smell loss is more common. That loss can be total or what's called hyposmia, a diminished sense of smell. Cowart says smell loss can happen when olfactory cells get damaged by things we inhale, by a head injury or by viruses.

COWART: Simple cold viruses will sometimes seem to attack those receptor neurons and cause a longer-term loss of smell due to damage to those neurons.

HEIST: Aging also plays a big role.

COWART: By the time people are in their - certainly their 70s and beyond, very few people escape without some degree of smell loss.

HEIST: That might cause some seniors to lose their appetite or over-season their food.

Nisha doesn't know how she lost her sense of smell, but she thinks she was born with one. As a little kid, she remembers liking food and eating. But...

PRADHAN: There came this point where I wasn't eating as much, or I - and I didn't show that much interest in food. That was probably when I lost my sense of smell.

HEIST: Nisha wonders whether her anosmia has affected more than her appetite. She thinks it may have affected her memory. Remember the smell of your elementary school cafeteria, the perfume of your first crush? That feeling where a certain smell instantly takes you back - Nisha doesn't get that feeling. And she's afraid it means parts of the past are missing.

PRADHAN: When I ask my sister about this - and she - she and I are not very far apart in age, but she remembers people and places and things we've done more vividly than I do.

PAUL MOORE: So what Nisha's probably experienced - and in part she's right, and she doesn't get that deep emotional attachment to the memories she's laying down.

HEIST: That's biologist Paul Moore, author of the book, "The Hidden Power Of Smell." Moore says smell memories are different from other memories. When you smell something, he says, it triggers a response in the limbic system, what he calls the emotional part of the brain.

MOORE: When olfactory memories come in or olfactory signals come in, you feel about them first. You don't process it. You don't think about it. You feel about it. And then you think about it. And then the memory is laid down.

HEIST: So without the feeling part, the thinking about it part doesn't come. That means no new smell memory gets created. There's no cure for congenital anosmia. Doctors can treat the inflammation or nasal blockage that may be causing acquired smell loss. And if the damage isn't too great, sometimes the sense of smell returns.

But it could take years if it happens at all. Researchers are also studying stem cells to see whether they can coax them into becoming new olfactory neurons. But human trials are years away, Cowart says. Nisha, she's not holding out hope for a cure anytime soon.

PRADHAN: Realistically - and maybe this is the premed in me. And I know a little bit about how research works and how long trials take to get medications or therapies out. For me, right now, the biggest concern is, can I really trust myself to live on my own?

HEIST: To know whether the milk in her fridge is spoiled or if she's burning something on the stove or if there's a gas leak - that would be enough for her for now. For NPR News, I'm Annette Heist.