If scientists were to design an experiment almost guaranteed to cause significant embarrassment, filming adolescents singing “Let It Go” from Frozen and then replaying their performance would likely do the trick.

Researchers at the University of Amsterdam did just that. They invited dozens of young volunteers into their lab, revealing that they would be filmed singing the Arendelle anthem or another chosen track in front of a camera. The participants then had to watch their performance playback inside a brain scanner.

By intentionally inducing embarrassment and using temperature sensors on the participants’ cheeks, scientists aimed to identify the neural activity associated with blushing, which Darwin described as “the most human of all expressions.”

Psychologists have two main theories about blushing. Darwin’s theory suggests that blushing occurs when we consider how we appear to others, while the alternative theory suggests it is a spontaneous response to feeling exposed.

Dr. Milica Nikolic, a psychologist and the study’s first author, explained: “Is it just being in the social situation where you are exposed and the center of attention, and you feel the exposure and attention from others? Or is it more complex, involving thoughts about how we look to others?”

The researchers recruited more than 60 young people aged 16 to 20, with almost all participants being female, leading the study to focus on young women. During their first lab visit, each volunteer performed karaoke while being filmed. The song choices included “Let It Go,” Adele’s “Hello,” Mariah Carey’s “All I Want For Christmas Is You,” and t.A.T.u’s “All The Things She Said,” all considered challenging to perform well, thus likely to cause embarrassment.

A week later, the volunteers returned to watch their performance and those of others while lying in a brain scanner. They were told others were watching their performance simultaneously, a tactic designed to increase their embarrassment.

As expected, participants blushed more while watching themselves than others. However, brain scan analysis suggested that blushing might not be triggered as Darwin theorized. Increased activity was observed in the cerebellum, associated with emotional arousal, and the visual cortex, indicating that participants were closely paying attention to their performance. There was no evidence that participants were thinking about how others might judge them.

“Blushing can come simply from being exposed,” said Nikolic. “In that very short moment, you maybe don’t think about how you look. I think it’s more automatic than the theory suggests.