The machine is built to find the alarm. Slide a person into a functional MRI scanner, flash images chosen to disturb — mutilated bodies, a toilet brimming with feces, scenes of violence — and somewhere deep in the temporal lobe a pair of almond-sized clusters will flare on the screen. This is the amygdala, the brain’s threat detector, and in nearly every human being given this test it lights up like a struck match. It is supposed to. That is its job.
In March 2016, at the Medical University of South Carolina in Charleston, the cognitive neuroscientist Jane Joseph ran the test on Alex Honnold. About two hundred images flickered past at channel-surfing speed. Joseph watched the amygdala for the flare.
It never came.
That dark screen is the evidence. The question it raises has rival answers that tell different stories about the same man — one in which Honnold barely feels fear at all, one in which he feels it and crushes it before it surfaces, one in which a lifetime of climbing wore the alarm down. The scan alone cannot choose between them.
The defendant
By 2016 Honnold was the most accomplished free-solo climber alive — a man who climbed enormous rock faces alone, with no rope, no harness, nothing to catch him if a foot slipped. He had soloed the 1,200-foot Moonlight Buttress in Zion, the northwest face of Half Dome, a parade of walls where a single mistake meant a fall of hundreds or thousands of feet onto stone. He lived out of a van. He didn’t drink, didn’t touch drugs, didn’t even take coffee. Among climbers he had earned the nickname “No Big Deal.”
The question about such a person is the one Joseph set out to answer: does he actually feel fear and override it, or does he simply not feel it? The amygdala is where you would look. It is the structure that takes in a threat before the conscious mind has finished registering it, and sets the body running — the spike of adrenaline, the tightening gut, the flood of alarm. People whose amygdalae are wrecked by disease lose the capacity for fear almost entirely. The most famous, a patient known in the literature as SM, has damage on both sides. Taken through a haunted house, she led the group, rated her own fear at zero the whole way through, and at one point startled a costumed monster by poking it in the head — she was curious what it would feel like. Handed a snake at a pet store, she touched its flicking tongue, then asked fifteen separate times whether she could handle one of the larger ones. The tissue that would have generated the dread was gone.
Honnold’s amygdala was not gone. On the structural scans his brain looked entirely normal — no damage, no missing piece. Whatever was different about him was not a hole. The dark screen had to mean something about how a fully intact threat detector was behaving.
The control: a brain that did light up
The first exhibit is what the scan looks like on someone else. Joseph did not test Honnold alone. For comparison she ran a second man through the identical protocol: another male rock climber, close to Honnold in age, already measured as a “high sensation seeker” — the personality type that chases thrills and novelty. If anyone’s brain should have stayed calm under a stream of gore, it was a fellow climber wired for risk.
It didn’t. On the scans of the two men’s responses to the high-arousal photographs, brain activity rendered in electric purple, the control climber’s amygdala “might as well be a neon sign,” Joseph said. Honnold’s stayed dark. At a reasonable statistical threshold there was, she found, no amygdala activation at all. Pushing the analysis to a looser setting coaxed out a single active voxel — one flickering speck, by which point, as Joseph put it, real data was indistinguishable from error.
The second task told the same story. Flip to the scans for a task built around monetary reward and the control climber’s amygdala, along with several other structures, looked in her words “like a Christmas tree lit up.” In Honnold’s brain the only activity was in the regions that process visual input — confirming little more than that he had been awake and looking at the screen.
And Honnold’s own account matched the picture from the inside. The gruesome images that are supposed to jolt a person did nothing for him. “I was like, whatever,” he said. Looking through them, he said, was “like looking through a curio museum.”
The first reading: the alarm is just quiet
Take the scan at face value and the explanation is the simple one: the alarm barely fires. Honnold may have “no internal reactions to these stimuli,” Joseph said — an amygdala that, for whatever reason, does next to nothing. On that account he is not a brave man conquering terror so much as a man with the volume turned down at the source. The body that should be screaming about the wall just stays quiet. He is closer to patient SM than to the rest of us, except that his hardware is entirely intact.
It is the cleaner story, and it makes the better headline: the fearless brain. Joseph would not quite sign off on it.
The other readings: the alarm fires, and something silences it
The subtler explanation is that the alarm does fire, and a downstream system shuts it off before it reaches the surface. “It could be the case,” Joseph offered, “that he has such a well-honed regulatory system that he can say, OK, I’m feeling all this stuff, my amygdala is going off, but his frontal cortex is just so powerful that it can calm him down.” On that account Honnold is not numb at all; he is exquisitely controlled, running the fear down so fast that even the scanner, which catches the alarm in nearly everyone, finds nothing left to catch.
There is a third version, and it does not ask you to choose. Joseph LeDoux, a New York University neuroscientist who has studied the brain’s threat response since the 1980s, told Nautilus he had never heard of a person born with a normal amygdala — as Honnold’s appears to be — that shows no sign of activation. His own explanation refused to separate what Honnold was born with from what he had made of himself. Honnold’s brain, LeDoux said, “is probably predisposed to be less reactive to threats that other people would be naturally responsive to, simply because of the choices he’s made. On top of that, these self-imposed strategies that he’s using make that even better, or stronger.” A lifetime of walking up to the thing that frightens you and doing it again is a known way to talk a threat detector down; the fear researcher Marie Monfils, quoted in the same piece, describes exactly that loop — “you experience some fear, but you overcome it, and you do it again and again and again.” On that account the dark screen is not a birthmark. It is a callus.
Every one of these readings predicts the same dark screen. The fMRI cannot separate a fire that never starts from a fire put out instantly, or from one that decades of practice taught not to catch — which is exactly why Joseph kept refusing to oversell what she had found. One man in a magnet, measured against one other man, scanned at the invitation of a magazine; a decade on, the result has never appeared as a peer-reviewed study. A sample of two settles nothing. Joseph herself called it an observation, not a study — and the popular versions that promoted it to “the fearless brain” were claiming more than she ever did.
The personality tests complicate the case
The cleanest verdict — a man simply born without fear — does not survive the rest of the data. Honnold scored about twice as high as average on sensation-seeking — and fully 20 percent higher than the average high sensation seeker — which fits any of the readings. But he also scored high on conscientiousness and low on neuroticism, and, more surprisingly, high on the impulsive traits — urgency, disinhibition — associated with rash decisions made without much thought for the consequences. Joseph had expected him to come out low there. He scored on the high end.
That last result points away from “fearless and therefore safe.” Joseph’s takeaway was less a celebration than a warning. Asked what caution she would offer Honnold on the strength of the scan and the surveys, she gave one line: “Don’t let the impulsivity win out over the conscientiousness.” The thing keeping Honnold alive, on that reading, was that the discipline kept winning, climb after climb. A man with a quiet amygdala and a loud impulsive streak is not safe by nature; he is safe only as long as the control holds.
El Capitan
The case never closed. A year and a few months after the scan, with every explanation still standing, Honnold did the thing they were arguing about.
On June 3, 2017, he parked in El Capitan Meadow in Yosemite, hiked up the boulder-strewn path to the base, and started up the granite in the pink light of dawn at 5:32 a.m. The route was Freerider — 3,000 feet of vertical and overhanging rock, graded 5.13a, a line most elite climbers struggle to finish with a rope. He carried none. He moved up the wall on fingertips and friction — a stretch of slab six hundred feet up where the only purchase is rubber pressed flat against the stone, “like walking up glass,” he said of it, and a notorious sequence of tiny holds where a slip would have been the end. At 9:28 a.m. he pulled himself over the lip of the summit, three hours and fifty-six minutes after he started.
It was the first free-solo ascent of El Capitan, and it was filmed; the resulting documentary, Free Solo, won the Academy Award for best documentary feature in February 2019. What the camera could not show was the thing in the scanner — that while a normal nervous system would have been screaming the whole way up, the alarm in Honnold’s head, whether quiet at the source, overruled from above, or worn smooth by a lifetime of practice, simply was not going off.
He said it himself, more plainly than any scan, and in a line that fits the quiet-alarm reading better than the throttled-alarm one: “If you don’t have any fear to begin with, there’s a lot less to control.”