A colleague recommended "Free Solo" to me a few years back. There was this part where the doctors claim (paraphrasing) his brain is unique in that he is much less afraid of danger than us. The part towards the end, where he does the actual climb of El Capitan in Yosemite National Park, is also worth watching.
I'm very skeptical of that claim. It seems just as reasonable that he has a perfectly normal brain that is exactly as afraid of things as the rest of ours, but he's spent a lot of time doing terrifying things and has learned to suppress how his body reacts to it.