Science Vs - The Woman Who Felt No Fear

Episode Date: June 11, 2026

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

Hi, I'm Wendy Zuckerman and you're listening to Science Verses. Today on the show, we are opening up a case file. This is where we report on case reports, which are curious stories from the scientific nerd literature, basically an end of one, a patient where something weird as happened to them. To go on this adventure, we have science journalist and friend of the show, Joel Werner. Hello. Hello, I'm a curious nerd. This is perfect. Let's go.

All right, Joel, to kick us. us off today, can you tell me about a time that you felt afraid? Very afraid. Look, it's a long list. My fear runs deep. Really? Are you afraid, he can? Oh, yeah, absolutely. I think the last time I felt truly afraid was when I found out how many people listened 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 swam out beyond the first breakers like the shore break where the first wave's crash. And we're catching some waves, you know, frolicing in the water. It's like a soda commercial. And then, yeah, 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 your, every gasp of air is a little bit shallower than the last one. Yeah, yeah, yeah. And you start panicking a little bit. Is that what you were doing? Oh, definitely. Yeah, yeah, yeah. I was, I was, it went from feeling like, you know, oh, I've been thrown around for

are 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. So what did you do? How did you get out? 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, yeah, it's pretty intimidating. 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.

They wouldn't, they wouldn't be scared at all. Wow. Someone who has nerves of steel. Like, not the frady cat that I am, I guess. Someone the complete opposite of you. And it's all coming up after the break. Visit BetMDM casino and check out the newest exclusive. The Price is Right Fortune Pick.

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We're bringing you a case file, strange reports, case reports from the literature. And we're here with Joel Werner. Hello, hello. Hello. 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 odour.

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. 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. 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. So she's a bit too much. We all know people like this, though. 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?

But there's some other reasons we might want to study it. 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 grey 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. It's quite exquisite.

What they saw was very much unprecedented at the time. It was these two bean-shaped patterns. patterns, hyper-intense, bright white patterns. So weird. It's so weird. Looking at the CT scans. It's so specific. It's really bizarre. Even neurosurgeon said, how is nature carving out this little almond-shaped nucleus and leaving the rest of the brain mostly intact?

So bright white patterns, like with an x-ray, does suggest there's something hard in your brain. Let me show you this CT scan. So you see those little... Oh, yeah. Like they jump out at you. It's almost like two sort of eyes within the brain. Yeah, little poked out eyes.

Yeah, not meant to be that. For you and me, presumably, yeah, that should look grey. So it turns out that SM has a genetic mutation that calcifies this very particular part of her brain. So the rest of her brain is fine if just these specific almond-shaped bits get calcified. Yes. It's so weird. It's so weird.

The condition is called Urbac-Vita disease. It does other things to your body, but in the brain, it's just really calcifying those two almond-shaped bits. That's so bizarre. And the bits that this disease is going after, very interesting. It's the amygdala. Ah, okay. Joel, you did it. I've dabbled in neuroscience in the past.

Yes. What is it, but what does the amygdala mean to you? 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. 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 is considered the fear center of the brain. 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 recognize fear, to feel fear. When you look at pictures of threatening animals and threatening people, your amygdala lights up. There have been studies into what happens. if we mess up an animal's amygdala. So rats who have lesions in their amygdala will go up to a cat. In fact, one of the rats in this very particular study nibbled on the cat's ear.

Cat didn't like that. No, no, not a wise decision if you're a rat. No, no. 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.

Yes. Yeah, they're playing a big role in that whole reaction that you're feeling. But if I have these calcified almonds in their place, then maybe I'm just like, lovely day for a surf today. Well, the question was, how would she react? 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 in the world of brain science. Justin said that at this University of Iowa, they basically collected patients with weird brain lesions and brain stuff going on. It's like a very specific type of Pokemon card. Like you've got to collect them all. They had like thousands of people with different brain conditions. Amazing. And with SM?

SM is one of the only living humans walking around this earth. without an amygdala. 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 would she react?

She's bungee jumping every weekend, going skydiving. Well, 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 Capitari. Oh, the Free Solo guy.

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. 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.

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 amygdala would be like, bing, big, bing, bing. And his was like, bong, bong, bong. So that is what's possible. And yet he still has an amygdala. Wow. And I just do want to say that the reason scientists wanted to get to the bottom of this, it's not just as a medical curiosity.

of what is SM capable of. But understanding what the amygdala does, understanding fear, 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 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. It's a very sort of classic experiment. 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 of what color hair they have, what color eyes they have. She could recognize anger and happiness and disgust. But then fear she had this whopping deficit. Wow. Yeah. She couldn't recognize when someone else was afraid. It's not that she just can't recognize emotion generally in people,

that she's picking up all of these other emotions, but then fear nothing. Yeah, the whopping deposition. 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 colors. And when a blue square would appear, the shape would be paired with a very loud boathorn.

Wow. Look, I had a boathorn and then forgot it at home. Like, I'm not going to 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. It was really loud. I also feel like what else are they conditioning? 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, but for SM, never flinched. What? Never had any reaction. They could not condition her to feel fear. Amazing.

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. 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. Snakes.

Fair. Now, it's interesting here because Justin and his colleagues think that SM's brain wasn't always like that 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. And she remembers at that time being extremely scared and yelling for her father to come get, out of it. But Justin Fig is, well, fast forward. Let's see how she reacts to snakes now. So he takes her to an exotic pet store. Picture it.

I don't know, 50 or so cages of different snakes. They had small ones, very tiny Slytherin snakes. They had really large ones that probably were almost 8 to 10 feet. Did she show any sign of feet? She did not. 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 flicking tongue and looking right into its eyes and going almost nose to nose. Wait, so she intellectually understood that she should have some kind of fear of snakes based on this early childhood experience. but she actually didn't feel the fear when confronted with this eight-foot snake.

Yeah, 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 going to get bitten. Some of these snakes are actually quite dangerous. Wow. And Justin thought maybe there was something about being in the pet store that made her kind of blizzard. 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 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, SM just grabs the snake, just throws it onto the grass, gets it away. and the sunset she seemed to feel this. Wow.

That's like some Steve Irwin-level snake handle in there. It's like, let's just get it out of here. I know. Justin takes it up a notch and takes her to a very scary spot. I can't believe you took her to a haunted house as part of a study. You know, 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. 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 describe this video. 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? 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? Yeah, okay, I'm out already. Like, if I'm there, I'm just like looking for the... It looks pretty weird, yeah.

I got to 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. 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. It was rating a nine on the haunted scale as deeply haunted. But it's a creepy place. 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. 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 strobing lights, the people hiding in weird corners. 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. Amazing. She's just like, cocktail hour. Exactly. Can we get that chainsaw on some lines? I want a Mahito.

She never screamed, never jump backwards, never flint. Justin wrote, She would gaze with amusement at the monstrous creatures, smiling or laughing at them in one instance, even scaring an actor. She's given it back. She's just like, I'm here to party. 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 are you feeling? 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 survival, you know? Like it's good to be afraid of things.

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. Don't believe the myth of trickle-down economics. Yeah, I mean, don't go down that street. Don't approach that person or that snake. Here's Justin again. 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. And not having a functioning amygdala, at times for SM, it has been rough. Her life has actually been at risk quite a few times. 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 Trunel. And SM told him this story. So it's nighttime. She's walking through a park near a church. I was walking to the store. And I saw this man on a park bench. Come here, please.

So I went over to him. He grabbed me. I did hurt, and he held a knife to my throat, and told me he was going to cut me. I told him, I said, go ahead and cut me. I said, I'll be coming back and I'll hunt your ass. Say that. I'm sorry. That's okay.

It's an intense situation. How did you feel when that happened? I wasn't afraid. and for some reason he let me go. And I went home. Probably. No. What an intense story.

She said, I got a knife held to her throat by a man in a dark park and still doesn't feel fear. Yes. And she told Justin this story too. And she even took him to the park where it happened. The way she describes it is she wasn't panicked. She could hear the church choir in the back. background actually practicing. And 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. Wow. Isn't that it's like, it's so, and the fact that she walked home, Justin said, he didn't run. She just walked. And I guess this is what we're talking about before when like, you know, fear is very useful because for most of us, if we're in that situation, we're not even approaching the creepy guy on the bench. We're clocking him and just getting out of there as soon as we can.

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. 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? That why, I mean, she also lives in an area that's not super safe. 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. But it's the sort of thing that if you live in that neighbourhood, and you've got kids.

I don't think I would be going to the cops. Keep your head down, right? Keep your head down. And whereas she doesn't have that level of fear. So she just was like, well, I don't want drugs in my neighborhood. Wow. Yeah. And like the other really sort of curious thing about these times is 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... The traumatic events do not seem to stick. It doesn't seem to have an imprint on her long term. So when you would ask her about these horrible events, how would she react?

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

After the break, forget snakes and haunted houses, Justin is going to try something completely different that may just change the way we think about fear. 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 frugless. 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? 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. But then Justin starts thinking, maybe I need to take a totally different approach here.

For years, actually decades, all of the things we had done to probe SM's fear had been external threats. sounds, sight. 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. 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. So is, is this like an awareness of your internal, like, you're hearing your, your heartbeat, you're like sensing the sort of breath going into your lungs? Is it, is it? 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 when it comes to breathing. 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. 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? Oh, absolutely, yeah. So let's do this experiment. Just breathe normally and then I want you to exhale all the air out of your lungs. Every last drop, and slowly go ahead. Take as big of an inhale as you can through the mouth all the way till you have no room left. And hold it and then let go.

And that's it. That's all it is. You do that. 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 870 times more carbon dioxide in it

than regular air. Yeah. 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 die, it's super dangerous. Now, this experiment is safe because you're just taking in one big breath of carbon dioxide. and then you can sort of balance things out quite quickly when you breathe out air,

you're kind of 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. You must have tried it on yourself, right? Oh, yes, definitely. I started noticing that I'm hyperventilating and it was automatic.

I'm just going, ha, ha, ha, ha, ha, ha. 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. So when I was thinking about these events that have happened in the surf where I've been

really afraid, I've 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 always felt that if I could just get a really big breath in, then I would feel a lot better. And this sounds like this is what this experiment is as well. Yeah, exactly. It was probably both the situation around you,

but then this intra receptive fear probably played a role in it as well. Exactly. Interesting. And so now let's go back to ESM 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? 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.

What do you mean by blunt it? Like she'd breathe it in and what would you see on her face? You would not see fear. You would not see this extreme hyperventilation response. Basically, he suspected she might have. some low-key reaction, but just like with the snakes and the haunted house, it was going to be a bust. And when SM walked into the lab that day, she didn't seem worried either. 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. She just takes a single breath of a bag of air that contains carbon dioxide. side. 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. Whoa, that must have been so intense for her. 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. Wow. So do they think that this introspective fear is like, modulated by a different part of the brain? Is there a different system going on? What's happening? Yeah. Okay. Well, so first he tested it with two other people. It was twin sisters who also had lesions in both of their amygdala's because of the same disease that SM has. Both of them got really scared to, 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. I mean, if you could have been a fly in 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. So ever since this fateful day, I've been racking my brain to try to understand how is this happening? Amazing.

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. Cells that are exquisitely sensitive to even small changes in carbon dioxide. 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 senses detect, uh-oh,

theory 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. That's right.

You drunk the red wine before writing that line, no doubt. Well, keep this in mind. It sounds a little hyperbolic, but it turns out it's absolutely true. 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.

And so these senses then emit that suffocation alarm to, and that, message ultimately gets sent into your brain. And now your brain is saying, my goodness, where is all this CO2 coming from? And that ultimately creates this feeling of fear and panic and oh my gosh, I'm going to 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. So when the CO2 hit the chemoreceptors of SM, those chemo receptors fired like it was a firework show. right? And then those messages got sent to the brain

and they must have generated that fear response bypassing any amygdala. Perhaps we don't even need the amygdala for this particular kind of fear response. So basically they're saying that 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. Exactly, exactly. And in fact, this 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, Urbacvite 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. And in that case, there was no CO2,

it just sort of happened spontaneously. And there are other studies in folks with fully functioning amygdala 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 center 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, obviously the individual is still important for fear because SM did all of these things. 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 intellectualized 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 are these biological senses that are kind of detecting it. It feels very low brain to me. Very lizard, right? Well, you know, that idea, that's kind of how, like, Justin sees it as well. I think one of the important lessons that SM has taught the scientific, world about 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. Got it. 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. And she actually called me the other day, And she was quite alarmed with what's happening in the world. And when a patient with bilateral amygdala lesions tells you, they're quite alarmed by something you listen. Wow. The world is such a dumpster fire that even the woman who cannot experience fear is afraid of what's going on.

That's science versus. Thank you so much, Del. Been a pleasure. Thanks, Wendy. Do you want to know how many citations are in this week's episode? Always. There are 51. Very solid.

Thanks, and if people want to see them, they can go to our show notes. And there's a look to the transcript. Thanks. Bye. Performance Auto Group's 37th annual sale event is back. Now for three days. Leaser finance from 0% plus loyalty incentives and maximum trade in value. Shop thousands of in-stock new, pre-owned and demonstrator vehicles.

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