In the 1930s, researchers discovered that when a certain part of monkeys’ brains was removed, the animals became fearless. They approached snakes, started batting them around like sticks and played with their hissing tongues.

This experiment has been repeated in animals numerous times, and the scientific consensus is that when the amygdala is removed, an animal loses any sense of fear.

Now, scientists have confirmed that a missing amygdala results in similar behavior in humans, according to a study in the journal Current Biology.

“There’s not very many humans with this sort of brain damage,” said Justin Feinstein, the study’s lead author and a clinical neuropsychologist at the University of Iowa. “Luckily for us, we had access to a patient, SM, and we studied her different fear behaviors and we read her personal diaries.”