The Woman Who Felt No Fear

A group of scientists meet a very unusual woman. A key part of her brain isn’t working: the amygdala. This is the part of the brain that we think is responsible for feeling fear. And in fact, this woman does seem pretty fearless. Researchers test her fear response using some very unconventional methods, but she takes everything in stride. Then, finally, they stumble onto the one thing that makes the woman who can’t feel fear absolutely panic. We scare up some science with neuropsychologist Dr. Justin Feinstein. Find our transcript here: https://tinyurl.com/ScienceVsWomanWhoFeltNoFear In this episode, we cover: (00:00) Meet the Woman Who Felt No Fear (04:38) Fear and the Amygdala (10:27) Scientists Start Running Experiments With the Woman Who Felt No Fear (11:48) Scientists Try to Scare SM (12:59) Scientists Try to Scare Her With Snakes (16:08) Scientists Try to Scare Her with a Haunted House (19:58) The Risks of Feeling No Fear (25:46) Scientists Try a New Approach (34:20) How Breathing Too Much Carbon Dioxide Causes Fear This episode was produced by Wendy Zukerman with help from Ekedi Fausther-Keeys, Rose Rimler, Michelle Dang, and Meryl Horn. We’re edited by Blythe Terrell. Mix and sound design by Bobby Lord. Music written by Emma Munger, So Wiley, Peter Leonard, Bumi Hidaka and Bobby Lord. Thank you to all the scientists we spoke to for this episode including, Special thanks to Joseph Lavelle Wilson and the Zukerman family. Science Vs is a Spotify Studios Original. Listen for free on Spotify or wherever you get your podcasts. Follow us and tap the bell for episode notifications. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Wendy Zukerman?

  Hi, I'm Wendy Zukerman and you're listening to Science Versus. Today on the show, we are opening up a case file.

• 0:11Wendy Zukerman?

  This is where we report on case reports, which are curious stories from the scientific nerd literature. Basically, an N of one, a patient where something weird has happened to them. To go on this adventure, we have science journalist and friend of the show, Joel Werner. Hello.

• 0:30Speaker 01

  Hello, I'm a curious nerd. This is perfect. Let's go.

• 0:33Wendy Zukerman?

  All right, Joel, to kick us off today, can you tell me about a time that you felt afraid? Very afraid.

• 0:40Speaker 01

  Look, it's a long list. My fear runs deep.

• 0:43Wendy Zukerman?

  Really? Are you a afraidy cat?

• 0:45Speaker 01

  Oh, yeah, absolutely. I think the last time I felt truly afraid was when I found out how many people listen to podcasts at double speed. What's wrong with you people? This is supposed to be a fun thing. You're supposed to relax. Don't rush through it. No, but seriously, growing up in Australia, I spent a lot of time in the ocean as a kid. And it's really easy for the ocean to go from being like an idyllic, beautiful day to being a near-death experience. And like, I have this one memory of being at a surf beach and I had gone to the beach with some friends and we'd sort of swum out beyond the first breakers, like the shore break where the first waves crashed. And we're catching some waves, you know, frolicking in the water. It's like a soda commercial.

• 1:31Speaker 01

  And then, yes, suddenly get dumped by a wave, get thrown around underwater, stick my head up, take in a breath. And as I come up, there's another wave crashing on me straight away. And so it happens again. And then I think when the waves hit in a particular frequency, then you suddenly just like you, every gasp of air is a little bit shallower than the last one.

• 1:52Wendy Zukerman?

  Yeah, yeah, yeah.

• 1:53Speaker 01

  And you start panicking a little bit.

• 1:54Wendy Zukerman?

  Is that what you were doing?

• 1:55Speaker 01

  Oh, definitely. Yeah, yeah, yeah. I was, I was, it went from feeling like, you know, oh, I've been thrown around for one or two waves to being like, if this keeps going, if I don't get out of this, then there's a good chance that something bad could happen.

• 2:10Wendy Zukerman?

  Well, so what did you do? How did you get out?

• 2:12Speaker 01

  Well, I ended up being able to swim with the waves. So I kind of caught a wave through to that shore break area. And then, once you can stand, you can kind of like stand up and battle the surf with your legs as well. But I think it's that feeling when you're just floating in the ocean and getting pummeled by the waves. It's, um, yeah, it's pretty intimidating.

• 2:30Wendy Zukerman?

  Well, today on the show, we're telling you about someone who would be in that situation and their heart might not even skip a beat.

• 2:39Speaker 01

  Hmm.

• 2:40Wendy Zukerman?

  They wouldn't, they wouldn't be scared at all.

• 2:42Speaker 01

  Wow. Someone who has nerves of steel, like not, not the fraidy cat that I am.

• 2:47Wendy Zukerman?

  Someone the complete opposite of you.

• 2:51Wendy Zukerman?

  And it's all coming up after the break.

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• 4:01Speaker 03

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• 4:36Wendy Zukerman?

  Welcome back. Today on the show, we're bringing you a case file, strange reports, case reports from the literature. And we're here with Joel Werner.

• 4:45Speaker 01

  Hello, hello.

• 4:46Wendy Zukerman?

  Hello. All right, we're going to jump right in. This is a story about a woman who we're going to call SM. And years ago, she started getting these strange spells, where she would smell a funny odor. And it was followed by this sensation of being detached, or feeling like she was watching herself from above. And so she gets a referral to the University of Iowa for a checkup, see what's going on.

• 5:17Wendy Zukerman?

  She heads there, and in a paper about SM, and kind of this moment, really, doctors describe her as pleasant and cheerful, but also quick to become friendly with examiners and experimenters. Which is exactly how Dr. Justin Feinstein, who worked at the University of Iowa, describes her.

• 5:38Speaker 04

  She's extremely friendly, she's very trusting. She starts speaking to you right away, as if you have this long history, as if she's already your friend. The next thing you know, she's asking personal details about your life, and she's telling you very personal details about her life.

• 5:59Speaker 01

  So she's a bit too much. We all know people like this, so this isn't, you know, we don't need to study people who are just like, don't know boundaries, don't understand social boundaries, right?

• 6:07Wendy Zukerman?

  But there's some other reasons we might want to study SM, right? So doctors start running tests to see what's going on with these spells. And they give her a CT scan, which uses a kind of X-ray on your brain. And normally with a CT scan, you just want to see a lot of gray brain. That's how, you know, you don't want to see like white patches in there, suggesting there's some bone somewhere in your brain. But here's what they saw when they looked at SM's brain.

• 6:36Speaker 04

  It's quite exquisite. What they saw was very much unprecedented at the time. It was these two bean shaped patterns, hyper intense, bright white patterns.

• 6:48Wendy Zukerman?

  So weird. It's so weird looking at the CT scans. It's so specific.

• 6:53Speaker 04

  It's really bizarre. Even neurosurgeons said, how is nature carving out this little almond shaped nucleus? And leaving the rest of the brain mostly intact.

• 7:06Wendy Zukerman?

  So bright white patterns, like with an X ray, does suggest there's something hard in your brain.

• 7:13Speaker 01

  Huh.

• 7:14Wendy Zukerman?

  Let me show you this CT scan. So you see those little?

• 7:20Speaker 01

  Ah, yeah. Like they jump out at you. It's almost like two sort of eyes within the brain.

• 7:26Wendy Zukerman?

  Yeah, little, little poked out eyes. Yeah, not meant to be there for you and me, presumably.

• 7:32Wendy Zukerman?

  Yeah, that should look great. So it turns out that SM has a genetic mutation that calcifies this very particular part of her brain.

• 7:43Speaker 01

  So the rest of her brain is fine. It's just these specific almond shaped bits get calcified.

• 7:48Wendy Zukerman?

  Yes, it's so weird.

• 7:49Speaker 01

  It's so weird. The condition is called Erbach-Viter disease.

• 7:53Wendy Zukerman?

  It does other things to your body, but in the brain, it's just really calcifying those, those two almond shaped bits.

• 8:01Speaker 01

  That's so bizarre.

• 8:02Wendy Zukerman?

  And the bits that this disease is going after, very interesting, it's the amygdala.

• 8:09Speaker 01

  Ah, okay.

• 8:11Wendy Zukerman?

  Joel, you didn't, you didn't have a brain.

• 8:14Speaker 01

  I've gabbled in neuroscience in the past.

• 8:16Wendy Zukerman?

  Yes. What is it? What does the amygdala mean to you?

• 8:19Speaker 01

  Well, given the story we were talking about before as well, which is like maybe a big clue. It sort of has something to do with the way that we process fear.

• 8:29Wendy Zukerman?

  Yes, yes, exactly. So the amygdala, we have two on each side of our brains. And but for SM, she has none. And it's really, the amygdala's. Considered the fear centre of the brain. Um. It does other stuff, but as one paper put it, in the minds of many scientists. The amygdala is synonymous with fear and basically many researchers have thought that you need it to feel fear. So we use the amygdala to recognise fear, to feel fear. When you look at pictures of threatening animals and threatening people, your amygdala lights up. There have been studies into like what happens if we mess up an animal's amygdala.

• 9:11Wendy Zukerman?

  Um. So rats who have lesions in their amygdala will go up to a cat. In in fact, one of the rats in this very particular study nibbled on the cat's ear. Cat didn't like that.

• 9:23Speaker 01

  No, no, not not a wise decision if you're a rat.

• 9:26Wendy Zukerman?

  No, no.

• 9:28Speaker 01

  So do they think that, so say when I'm out in the surf and I'm getting pounded by these waves and then I start to think, oh, maybe I can't get out. And that panic feeling overwhelms my brain. That's the neurons in my amygdala are firing off.

• 9:43Wendy Zukerman?

  Yeah, yeah, yeah, they're playing a big role in that rea- that whole reaction that you're feeling.

• 9:49Speaker 01

  But if I have these calcified almonds in their place, then maybe I'm just like, lovely day for a surf today.

• 9:55Wendy Zukerman?

  Well, the question was, how would she react?

• 9:58Speaker 01

  Hmm.

• 9:58Wendy Zukerman?

  Particularly at this stage when doctors are just meeting her. And this is exactly what they wanted to know. Because she is so unique here. Um. In the world of like brain science, Justin said that at this University of Iowa, they basically collected patients with weird brain lesions and brain stuff going on.

• 10:20Speaker 01

  Like a very specific type of Pokemon card, like you've got to collect them all.

• 10:24Wendy Zukerman?

  They had like thousands of people with different brain conditions.

• 10:27Speaker 01

  Amazing.

• 10:27Wendy Zukerman?

  And with S M.

• 10:29Speaker 04

  S M is one of the only living humans walking around this earth without an amygdala.

• 10:37Wendy Zukerman?

  So researchers wanted to study her and researchers like Justin to find out what does this mean? Does she really not feel fear? Would she really go into that water? And how what how would she react?

• 10:48Speaker 01

  She's bungee jumping every weekend, going skydiving.

• 10:51Wendy Zukerman?

  Well. Great, great example because just to give you a bit of context about what's possible here. Do you know who Alex Honnold is? He's a climber who climbed El Capitan.

• 11:04Speaker 01

  Oh, the Free Solo guy.

• 11:06Wendy Zukerman?

  Yes, yes, yes, yes. Okay. So he, for those who don't know, there was a documentary about him called Free Solo. He climbed this cliff, 3,000 feet, up into the air without a harness, without a rope, just him on his own.

• 11:23Speaker 01

  I feel like my amygdala was like working overtime just watching that documentary. I was having sweaty palms, like that sinking feeling in your stomach.

• 11:31Wendy Zukerman?

  And so he has a functioning amygdala, but researchers have found that it's a little bit tamped down. So when they did some studies on him, they were like, they showed him images that with you and me, our amygdalas would be like ping, ping, ping, ping, ping, and his was like boing, boing, boing. So, so that is what's possible and, and yet he, he still has an amygdala.

• 11:55Speaker 01

  Wow.

• 11:56Wendy Zukerman?

  And I just do wanna say that the reason scientists wanted to get to the bottom of this, it's not just as a medical curiosity of what, what is SM capable of, but understanding what the amygdala does, understanding fear, could, could help us with many different things. It could help us understand how we all understand fear. It could help us unravel treatments for PTSD and anxiety, which in some cases are thought to be where your fear response is, is maybe a little different to other people. So the researchers start doing experiments on SM. And they start simple, like at first they'll show her these photos of people's faces with different expressions on them. This is a very classic experiment.

• 12:40Speaker 04

  Surprise and disgust and anger and happiness and fear. She clearly could see the picture. She could tell if it's male or female. She could tell you all the description of what color hair they have, what color eyes they have.

• 12:55Wendy Zukerman?

  She could recognize anger and happiness and disgust.

• 12:59Speaker 04

  But then fear, she had this whopping deficit.

• 13:03Speaker 01

  Wow.

• 13:03Wendy Zukerman?

  Yeah, she couldn't recognize when someone else was afraid.

• 13:07Speaker 01

  It's not that she just can't recognise emotion generally in people, that she's picking up all of these other emotions, but then fear, nothing.

• 13:15Wendy Zukerman?

  Yeah, the whopping deficit. It's very strange, right? Next, they wanted to know, basically, could we scare her? And they really wanted to do what's called condition this fear response into SM. So what they do is they show her slides with different colours.

• 13:32Speaker 04

  And when a blue square would appear, the shape would be paired with a very loud boat horn.

• 13:45Speaker 01

  Wow.

• 13:46Wendy Zukerman?

  Look, I had a boat horn and then forgot it at home.

• 13:52Speaker 01

  Like, I'm not gonna lie, I'm kind of thankful that I didn't get pranked by a blowhorn. This isn't like early 2000s reality TV. This is serious science journalism here.

• 14:05Wendy Zukerman?

  It was really loud. I was...

• 14:07Speaker 01

  I also feel like what else are they conditioning?

• 14:08Wendy Zukerman?

  Well, the thing is, if you, for you and me, it wouldn't take that long to show us the blue square, pair it with the loud sound, and then as soon as we see the blue square, we'll be like, huh. But for SM, never flinched.

• 14:22Speaker 01

  What?

• 14:24Wendy Zukerman?

  Never had any reaction. They could not condition her to feel fear.

• 14:28Speaker 01

  Amazing.

• 14:29Wendy Zukerman?

  All right, they ask her questions out in the real world. Have you ever been scared? And they get into specifics, asking her questions about things that, you know, a lot of people are scared of.

• 14:38Speaker 04

  What kind of animals do you not like? Is there anything that maybe you're afraid of? Or you just don't find very pleasant? And she goes, well, I'm not really afraid of any animals, but I just don't like snakes. She kept saying that.

• 14:54Wendy Zukerman?

  Snakes.

• 14:54Speaker 01

  Fair.

• 14:56Wendy Zukerman?

  Now, it's interesting here because Justin and his colleagues think that SM's brain wasn't always, like, the amygdala wasn't always calcified in that way, and that it actually started in her adolescence. And maybe when she was younger, she had an amygdala, because she had stories that when she was little, she did feel fear. And she told this story that when she was on a hike with her dad, she actually fell into this pit of baby snakes.

• 15:26Speaker 04

  And she remembers at that time being extremely scared and yelling for her father to come get her out of it.

• 15:33Wendy Zukerman?

  But Justin figures, well, fast forward.

• 15:37Wendy Zukerman?

  Let's see how she reacts to snakes now. Uh, so he takes her to a exotic pet store. Picture it.

• 15:46Speaker 04

  I don't know, fifty or so cages of, of different snakes.

• 15:49Wendy Zukerman?

  Whoa.

• 15:50Speaker 04

  They had small ones, very like tiny, uh, slithering snakes. They had really large ones that probably were almost eight to ten feet.

• 16:01Wendy Zukerman?

  Did she show any sign of fear?

• 16:03Speaker 04

  She did not. It, it was so fascinating. In fact, it was the exact opposite. She was extremely curious. You know, I'll never forget her holding one of the snakes and touching its, its flicking tongue and looking right into its eyes and going almost nose to nose.

• 16:22Speaker 01

  Wait, so she intellectually understood that she should have some kind of fear of snakes based on this early childhood experience?

• 16:30Wendy Zukerman?

  Yes.

• 16:30Speaker 01

  She actually didn't feel the fear when confronted with this eight foot snake?

• 16:36Wendy Zukerman?

  Yeah, even though, even though she had said, I'm, you know, I don't like them. She showed no sign of that. And in fact, at one point, the employee at the store had to tell her, like, stop trying to touch the snakes because we think you're gonna get bit and some of these snakes are actually quite dangerous.

• 16:52Speaker 01

  Wow.

• 16:53Wendy Zukerman?

  And Justin thought maybe there was something about being in the pet store that made her kind of blasé about snakes, like maybe, you know, it felt like a safe environment. And so he asked her son, one of her sons, has she ever showed, you know, this kind of fear in the, in the real world? And her son actually told this story of a time where he and his other brother were playing in the yard and they see this really big snake. And they say, oh my God. And again, S M just grabs the snake, just throws it onto the grass, gets it away. And the son said she seemed sort of fearless.

• 17:31Speaker 01

  Wow. That's like some Steve Irwin level snake handling there.

• 17:36Wendy Zukerman?

  Yeah.

• 17:36Speaker 01

  It's like, let's just get it out of here.

• 17:37Wendy Zukerman?

  I know. Uh, Justin takes it up a notch and takes her to a very scary spot.

• 17:46Wendy Zukerman?

  I can't believe you took her to a haunted house as part of a study.

• 17:51Speaker 04

  You know, and, and, and it wasn't just any haunted house. It was Waverly Hills Sanitarium, which is considered one of the most haunted places in the world.

• 18:00Wendy Zukerman?

  Okay, so Waverly Hills Sanatorium in Kentucky used to be a hospital for tuberculosis patients and a lot of people died there. A lot of people died. And it closed down decades ago, was abandoned, but now you can go on tours there. The sanatorium even has a TikTok account. So Joel, I want you to take, to describe this video. It, it, it is scary. It looks like, I mean, I'm not into haunted houses, but this looks like a scary place. What are you seeing?

• 18:31Speaker 01

  Okay, so there's like, it's a very Gothic looking building. There's gargoyles on the top. Oh, we're going down some creepy stairs. Yeah. Oh, what's that on the walls?

• 18:45Speaker 01

  Yeah, okay, I'm out already. Like if I'm there, I'm just like.

• 18:48Wendy Zukerman?

  It looks truly scary, right?

• 18:50Speaker 01

  It looks pretty weird, yeah.

• 18:53Speaker 01

  I gotta say though, it's kind of weird hearing a scientist talk about like one of the most haunted places in America. It's like, buddy, come on.

• 19:00Wendy Zukerman?

  What's even funnier here is that other papers have cited this paper with quite seriousness and been like, look, they even took her to a haunted house, guys. So.

• 19:12Speaker 01

  It was rating a nine on the haunted scale as, uh, deeply haunted.

• 19:17Wendy Zukerman?

  But it's, it's, it's.

• 19:18Speaker 01

  It's a freaky place, yeah.

• 19:19Wendy Zukerman?

  It's a creepy place. And when Justin took SM, it was actually Halloween, when the owners of the sanatorium really go to town and they create this very intense experience.

• 19:30Speaker 04

  It was extremely creepy. Imagine, you know, going in through very dark corridors into rooms that you can't really tell what's on the other side. Really loud bangs and startling sounds going off. Chainsaws coming out, the, the strobing lights, the people hiding in weird corners. It was, it was managing to scare me, but there was SM leading us into battle saying, this way, guys, follow me, go through this hallway. Now let's go through this. She was having a blast.

• 20:02Speaker 01

  Amazing. She's just like, cocktail hour.

• 20:06Wendy Zukerman?

  Exactly.

• 20:07Speaker 01

  Can we get that chainsaw on some lines? I want a mojito.

• 20:12Wendy Zukerman?

  She never screamed, never jumped backwards, never flinched. Justin wrote, she would gaze with amusement at the monstrous creatures, smiling or laughing at them, in one instance even scaring an actor.

• 20:27Speaker 01

  She's giving it back. She's just like, I'm here to party.

• 20:32Wendy Zukerman?

  Exactly. And I have to say that at this point, reading about SM, I was a little bit jealous about what it would be like to have no amygdala, to live like that, just to think of all the things that I haven't done in my life because I've been afraid. And she feels no fear. How, how are you feeling?

• 20:52Speaker 01

  I don't know, like, I feel like fear, like, and, you know, correct me if I'm wrong, but I feel like fear plays an important part in like our, our survival, you know, like it's good to be afraid of things.

• 21:05Wendy Zukerman?

  That is exactly what Justin said. Justin was like, you know, we need that spidey sense telling us, don't jump into that water, don't eat those poisonous berries.

• 21:16Speaker 01

  Don't believe the myth of trickle down economics.

• 21:19Wendy Zukerman?

  Don't, yeah, I mean, don't go down that street, don't approach that person or that snake. Um, here's Justin again.

• 21:27Speaker 04

  The whole point of fear is to teach you something, right? So the amygdala's role is really to keep you alive and to keep you away from the things that can kill you.

• 21:38Wendy Zukerman?

  And not having a functioning amygdala at times for SM, it has been rough.

• 21:44Speaker 04

  Her life has actually been at risk quite a few times.

• 21:49Wendy Zukerman?

  So researchers like Justin, who study SM, have protected her privacy very carefully and no journalists have ever been able to talk to her. But several years ago, when Alex Spiegel was co-hosting the NPR podcast, Invisibilia, she was able to send a short list of questions to one of the neuroscientists who's been studying SM for the last few decades. His name is Daniel Trinell. And SM told him this story. So it's nighttime, she's walking through a park near a church.

• 22:18Speaker 05

  I was walking to the store and I saw this man on a park bench.

• 22:25Speaker 05

  He said, "Come here, please." So I went over to him. I said, "What do you need?" He grabbed me by the hair and he held a knife to my throat and told me he was gonna cut me. I told him, I said, "Go ahead and cut me." And I said, "I'll be coming back and I'll hunt you." Oops, am I supposed to say that? I'm sorry.

• 22:51Speaker 06

  That's okay, it's a, it's an intense situation. How did you feel when that happened?

• 22:57Speaker 05

  I wasn't afraid. And for some reason, he let me go. And I went home.

• 23:05Speaker 06

  Called the police?

• 23:07Speaker 05

  No.

• 23:09Speaker 01

  What an intense story. She's got a knife held to her throat by a man in a dark park and still doesn't feel fear.

• 23:16Wendy Zukerman?

  Yes, and she told Justin this story too. And she even took him to the park where it happened.

• 23:22Speaker 04

  The way she describes it is she wasn't panicked. She could hear the, the church choir in the background actually practicing. And it, it sounds like the guy may have been a little freaked out by how calm she was and he let her go and she walked home.

• 23:42Speaker 01

  Wow.

• 23:43Wendy Zukerman?

  Isn't that, it's like, it's so... And the fact that she walked home, Justin said, "She didn't run. She just walked."

• 23:51Speaker 01

  And, and I guess this is, this is what we're talking about before when like, you know, fear is very useful because you, for most of us, if we're in that situation, we're not even approaching the creepy guy on the bench. We're, we're clocking him and just getting out of there as soon as we can.

• 24:06Wendy Zukerman?

  Yeah, and it's not just this incident with the knife. At another time, a stranger put a gun to her head, yelled at the top of his lungs, "Bam!", before running away. That didn't scare her. SM said she found the whole experience strange.

• 24:20Speaker 01

  So are there situations where anyone with a functioning amygdala would be out of there? Would have sort of sensed the fear in the moment and would have sort of extracted themselves from that situation? But for her, because she doesn't have that ability, her brain just doesn't experience that fear. She just stays in the situation until it's too late, essentially, and people are pulling knives and pulling guns on her. Is that sort of what they think is happening?

• 24:47Wendy Zukerman?

  That why, I mean, she also lives in a, in an area that's not super safe.

• 24:54Speaker 01

  Mm-hmm.

• 24:54Wendy Zukerman?

  There is a lot of violence, there's a lot of drug violence where she lives. And in that instance with the gun, how it happened is that her kid had found some drugs in the yard and she suspected who it was in the neighbourhood who was dealing and went to the police and just said, that's that person. And as a result was getting a bunch of threatening letters, including a gun being pointed at her.

• 25:18Speaker 01

  Wow.

• 25:18Wendy Zukerman?

  But it's the sort of thing that if you live in that neighbourhood, I don't, and you've got kids, I don't think I would be going to the cops.

• 25:26Speaker 01

  You keep your head down, right?

• 25:27Wendy Zukerman?

  Keep your head down. And whereas you don't, she doesn't have that level of fear, so she just was like, well, I don't want drugs in my neighbourhood.

• 25:34Speaker 01

  Wow.

• 25:35Wendy Zukerman?

  Yeah. And like the other really sort of curious thing about these times is if it, if any of this stuff happened to you and me, it would stay with us. We would, you know, for weeks, you know, months maybe, maybe years, we would be thinking over this time about how terrible it was, you know, because the amygdala plays such an important role in like capturing those memories. But maybe it's not so surprising that with SM.

• 26:05Speaker 04

  The traumatic events do not seem to stick. It doesn't seem to have an imprint on her long term.

• 26:13Wendy Zukerman?

  So when you would ask her about these horrible events, how would she react?

• 26:18Speaker 04

  She would tell you very matter of factly what had happened. And in some cases, she would actually tell you it with, with a bit of pride, like, look what, you know, I've, I've had to overcome in life.

• 26:31Wendy Zukerman?

  So by this point, when it comes to sort of Justin's journey of trying to scare SM and doing all these experiments over years, I mean, he's really thinking, this woman just cannot feel afraid.

• 26:47Speaker 04

  She seemed fearless.

• 26:51Wendy Zukerman?

  After the break, forget snakes and haunted houses. Justin is gonna try something completely different that may just change the way we think about fear.

• 27:10Speaker 03

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• 29:14Wendy Zukerman?

  Okay, welcome back. Here's where we're at. Scientists have basically been trying to scare a woman who can apparently feel no fear. A part of her brain, the amygdala, that we think is critical for feeling fear, does not work in her brain. So this mission is feeling a little bit frivolous. And as a reminder, scientists aren't just doing this for kicks. They're doing this to help us all understand how we feel fear. But I wanted to know, that's why scientists are interested in this. Why is... What about SM? So I asked Justin. Why was she up for this? Like, she's been studied for decades. Why does she let herself do this?

• 29:53Speaker 04

  You know, I think for her, she's actually quite curious as well about her condition. She knows that she's different. She knows that she obviously has this brain injury. Before this study, she didn't really fully understand how deep her lack of fear went.

• 30:09Wendy Zukerman?

  But then Justin starts thinking, maybe I need to take a totally different approach here.

• 30:15Speaker 04

  For years, actually decades, all of the things we had done to probe SM's fear had been external threats. Sounds, sight.

• 30:29Wendy Zukerman?

  But what if, in the words of Zeus, we need to look inside ourselves? Because there is this fear response that we have that has nothing to do with what we can see or hear, but it comes from within. And it's called interoceptive fear.

• 30:45Speaker 04

  I'm talking about the brain's ability to sense. The inside of your body, the viscera of the body. So like the heart, the gut, your whole respiratory system, for example.

• 30:57Speaker 01

  So this is, is this like an awareness of your internal like system? Like you're hearing your, your heartbeat, you're like sensing the sort of breath going into your lungs. Is it, is it?

• 31:07Wendy Zukerman?

  Exactly, exactly. And so when things go wrong inside our body, sometimes it can make us feel afraid. And so the best example of this, I think, is, is when it comes to breathing.

• 31:19Speaker 04

  From the moment we wake up until the moment we go to sleep. And even while we're sleeping, we're just breathing, right? We take it for granted.

• 31:27Wendy Zukerman?

  We breathe in oxygen, we breathe out carbon dioxide. It's this beautiful, delicate dance. Our body is happy. But here's what happens if you screw up that dance for just a moment. So there's this experiment that Justin likes to do. Joel, will you do it with me?

• 31:43Speaker 01

  Oh, absolutely, yeah.

• 31:44Wendy Zukerman?

  So let's do this experiment.

• 31:46Speaker 04

  Just breathe normally. And then I want you to exhale all the air out of your lungs. Every last drop, nice and slowly, go ahead.

• 31:57Speaker 04

  Take as big of an inhale as you can through the mouth, all the way till you have no room left.

• 32:04Speaker 04

  And hold it and then let go. And that's it. That's all it is, is you do that.

• 32:12Wendy Zukerman?

  Okay, except there is one very important difference between what we just did and the actual experiment. Instead of breathing in regular air, which is actually quite nice, you breathe in a bag of air that has eight hundred and seventy times more carbon dioxide in it.

• 32:28Speaker 01

  Ah.

• 32:29Wendy Zukerman?

  Than regular air.

• 32:30Speaker 01

  Yep.

• 32:31Wendy Zukerman?

  So there's quite a lot of CO2. And when people do this experiment, they can get really scared and think that they're going to die. And that's because normally if your CO2 levels go through the roof and your oxygen levels dive, it's super dangerous. Now, this experiment is safe because you're just taking in one big breath of carbon dioxide and you can sort of balance things out quite quickly. When you breathe out air, you're gonna get rid of that carbon dioxide quickly. Also, your oxygen levels are fine throughout the experiment, but still, your brain, your body gets confused and people can panic. Did you, you must have tried it on yourself, right?

• 33:09Speaker 04

  Oh, yes, definitely. I started noticing that I'm hyperventilating and it was automatic. I'm just going and like all of a sudden, the periphery of the world feels, is like getting a little darker. And then in my mind, the only thing I could think about at the time was, if this continues, I'm going to suffocate.

• 33:33Speaker 01

  So when I was thinking about this, uh, these events that have happened in the surf, where I've been really afraid, I thought that the one thing that was driving my fear reaction was the lack of oxygen, was like I wasn't getting enough air into my lungs. I wasn't getting enough oxygen into my body. And I think, I, I always felt that if I could just get a really big breath in, then I would feel a lot better.

• 33:58Wendy Zukerman?

  Right.

• 33:58Speaker 01

  And this sounds like this is what this experiment is as well.

• 34:01Wendy Zukerman?

  Yeah, exactly. It was probably both the situation around you, but then this interoceptive fear probably played a role in it as well. Exactly.

• 34:09Speaker 01

  Interesting.

• 34:10Wendy Zukerman?

  And so now let's go back to SM because Justin and his colleagues wanted to know how would she react to this? What did you think would happen with SM going into that day?

• 34:21Speaker 04

  Keep in mind the context that I had just spent, you know, the past five years trying my best to find a way to scare SM. And so my expectation is that her response was going to be blunted.

• 34:35Wendy Zukerman?

  What do you mean by blunt? Like she'd breathe it in and what would you see on her face?

• 34:39Speaker 04

  You, you would not see fear. You would not see this extreme hyperventilation response.

• 34:46Wendy Zukerman?

  Basically, he suspected she might have some low-key reaction, but just like with the snakes and the haunted house, it was gonna be a bust. And when SM walked into the lab that day, she, she didn't seem worried either.

• 34:57Speaker 04

  She was her normal self. We're hooking her up to all these different sensors to measure different things. We're putting this breathing mask on her. No sense of fear or anticipatory anxiety. She seems very calm, talking to us, chit-chatting and whatnot.

• 35:13Speaker 04

  She just takes a single breath of a bag of air that contains carbon dioxide. One breath, that's all it is. And this is where things get interesting. Within about a few seconds, she starts waving her hand, saying, "Help me, help me." And then she starts trying to tear off her face mask. When you look at her eyes, her eyes were wide open like a deer in headlights. Never seen that before in SM. And then afterwards, when we talked to her, it took several minutes for her to calm down from this experience. We asked her, "What happened?" And her response was, "I have never felt anything like that before. I felt fear."

• 35:59Speaker 01

  Whoa. That must have been so intense for her.

• 36:03Wendy Zukerman?

  Yeah, yeah. I mean, I think so. I think she remembered it. Later, when Justin would talk to her, she'd say, "I never want to do that experiment again."

• 36:13Speaker 01

  Wow. So do they think that this interceptive fear is like modulated by a different part of the brain? Is there a different system going on? What's happening?

• 36:22Wendy Zukerman?

  Yeah, okay. Well, so first, he tested it with two other people. It was twin sisters who also had lesions in both of their amygdalas because of the same disease that SM has. Both of them got really scared too, gasping for air, looking very distressed, wanting to rip off the inhalation mask. It was all, this was all quite shocking because it showed that contrary to what science thought, that the amygdala is essential for fear. I mean, all of a sudden, it wasn't. So here's Justin.

• 36:54Speaker 04

  I mean, if you could have been a fly on the wall in the laboratory that day, our eyes were wide open, our jaw was agape. We were all dumbfounded because this was the exact opposite of what we had expected to happen. You know, for the better part of a half a century, it was always presumed that the amygdala was required to feel fear, to feel panic. And for the first time, we have a human who is lacking this structure in their brain. No longer has the amygdala, yet still felt fear and panic. Where is this happening in the brain? How is this happening in the brain? These were the types of questions spiraling through my head.

• 37:37Speaker 04

  So ever since this fateful day, I've been racking my, my brain to try to understand how is this happening?

• 37:47Speaker 01

  Amazing.

• 37:48Wendy Zukerman?

  So generally speaking, the reason that all of us can get panicky when we have too much carbon dioxide is because we have these chemical sensors in our blood and throughout our body that detect if the blood is getting too acidic.

• 38:01Speaker 04

  Cells that are exquisitely sensitive to even small changes in carbon dioxide.

• 38:08Wendy Zukerman?

  And that's because we really need to know if there is too much carbon dioxide in our body. If it happens, it makes our blood more acidic. If our blood gets too acidic, organs can fail. So when these sensors detect, uh oh, CO2 levels are too high, they emit suffocation alarms? Or as Justin wrote in a paper, quote, "A proverbial primal scream aimed at alerting the nervous system of impending demise."

• 38:37Speaker 04

  That's right.

• 38:38Wendy Zukerman?

  Well, you drunk the red wine before writing that line, no doubt.

• 38:43Speaker 04

  Well, keep, keep this in mind. It, it, it sounds a little hyperbolic, but it turns out it's absolutely true. If, if you breathe that level of CO2 for even one to two minutes, it could kill you. This panic response, this alarm is a real alarm. It's trying to alert you essentially that the pH of your blood is dropping. It's becoming acidic.

• 39:07Wendy Zukerman?

  And so these sensors then emit that suffocation alarm to, and that message ultimately gets sent into your brain.

• 39:15Speaker 04

  And now your brain is saying, my goodness, where is all this CO2 coming from?

• 39:19Wendy Zukerman?

  And that ultimately creates this feeling of fear and panic and oh my gosh, I'm gonna die. And so to go back to why did SM have this feeling? Well, like the rest of us, she has those sensors that detect carbon dioxide levels.

• 39:34Speaker 04

  So when the CO2 hit the chemoreceptors of SM, those chemoreceptors fired like it was a fireworks show, right?

• 39:43Wendy Zukerman?

  And then those messages got sent to the brain and they must have generated that fear response by passing any amygdala. Perhaps we don't even need the amygdala for this particular kind of fear response.

• 39:56Speaker 01

  So basically, they're saying that like for decades, we've thought that the amygdala is necessary for the experience of fear. And now they're saying that fear can be experienced in other parts of the brain.

• 40:09Wendy Zukerman?

  Exactly, exactly. And in fact, the study, this study of SM with the carbon dioxide, it's since been cited hundreds of times as evidence for this exact thing, that you can experience fear without an amygdala. And there's other research, it's not just this, that's showing this kind of thing. Even when there's no carbon dioxide around, we are seeing people experiencing fear not involving the amygdala. So for example, there's another patient that had damage to both of his amygdala, also had that same disease, Erbukvete disease. And all of a sudden with him, he just developed these really nasty panic attacks where he'd get heart palpitations and have a fear of dying.

• 40:51Wendy Zukerman?

  And in that case, there was no CO2, it just sort of happened spontaneously. And there are other studies in folks with fully functioning amygdalas that have found that other areas of the brain are lighting up in this kind of fear network. And maybe the amygdala isn't this fear centre that we thought it was. Maybe it's, I mean, it is really making us think of fear in this totally new way. You know, we, obviously the amygdala is still important for fear because SM did all of these things.

• 41:25Speaker 01

  Yeah, it's the idea that there are maybe different types of fear as well, but we've been labelling this whole sort of gamut of emotions with the label fear. But like something like, you know, if you're afraid of a snake, there's a sort of intellectualised component to that, right? Like you have to have learnt at some point that snakes are bad. Whereas like this, it sort of seems like a more kind of physiological process where it's like you've got the extra carbon dioxide in your blood there. There are these biological senses that are kind of detecting it. It feels very low brain.

• 41:58Wendy Zukerman?

  Very lizard, right? Well, you know, that, that idea, that's kind of how like Justin sees it as well.

• 42:05Speaker 04

  I think one of the important lessons that SM has taught the, the scientific world about the, the neuroscience of fear is that there's probably not one type of fear that is all encompassing and is in one specific brain area.

• 42:26Speaker 01

  Got it.

• 42:27Wendy Zukerman?

  And just to cap us off, it's been about 10 years since that study that Justin did with SM has been published. And these days, Justin doesn't really study SM, but they are still in touch.

• 42:39Speaker 04

  And she actually called me the other day and she was, she was quite alarmed with what's happening in the world. And when, when a patient with bilateral amygdala lesions tells you, uh, uh, they're quite alarmed by something you listen.

• 42:55Speaker 01

  Wow.

• 42:57Speaker 01

  The, the world is such a dumpster fire that even the woman who cannot experience fear is afraid of what's going on.

• 43:05Wendy Zukerman?

  That's science versus.

• 43:09Wendy Zukerman?

  Thank you so much, Joel.

• 43:11Speaker 01

  Been a pleasure. Thanks, Wendy.

• 43:12Wendy Zukerman?

  Do you want to know how many citations are in this week's episode?

• 43:14Speaker 01

  Always.

• 43:15Wendy Zukerman?

  There are 51.

• 43:17Speaker 01

  Very solid.

• 43:19Wendy Zukerman?

  Thanks. And if people want to see them, they can go to our show notes and there's a link to the transcript. Thanks.

• 43:25Speaker 01

  Bye.

• 44:10Speaker 07

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