But the scientists weren’t done embarrassing the volunteers. In the weeks after singing, the participants returned to the lab to watch a video of their performance while an MRI exam studied how much they blushed and which parts of their brains activated that blushing.

The resulting study, published Wednesday in the journal Proceedings of the Royal Society B, found that most of the 40 participants blushed while watching themselves sing due to increased activity in the cerebellum, an area of the brain that has been found to help process emotions. The researchers said that the blushing was probably an automatic emotional response to feeling exposed.

Most people have blushed while feeling self-conscious, embarrassed or ashamed. Biologist Charles Darwin, who developed the theory of evolution, once called blushing “the most peculiar and the most human of all the expressions.”

Research has found that people blush when they watch videos of themselves that they find embarrassing. Nikolić, a professor of developmental psychopathology at the University of Amsterdam, and her fellow scientists thought participants might feel vulnerable while watching themselves sing karaoke. They selected a subject group with ages 16 through 20 because research has found that people in that age group are more likely to feel self-conscious about how they’re perceived.

For the music, they sought out songs that are hard to sing so that participants would be more likely to make a mistake and feel embarrassed, Nikolić said. Researchers also wanted the music to be popular among the subject group, she said, so the singers would notice their mistakes. They consulted music experts, who helped them rule out songs that might be too old for their subjects to spot those mistakes, such as ABBA’s 1975 hit “Mamma Mia.”

The researchers settled on four songs: “Hello” by Adele, “Let It Go” by Idina Menzel, “All I Want For Christmas Is You” by Mariah Carey and “All The Things She Said” by Russian pop duo t.A.T.u.

When the study began in the summer of 2020, participants visited the University of Amsterdam’s behavioral science lab, put on a pair of black headphones and sang the lyrics that appeared on a screen. Meanwhile, a camcorder filmed them.

The participants returned in the following weeks to lie in an MRI machine that examined their brains and the temperature of their cheeks. Blood flow to the face increases during blushing, causing the temperature of the skin to increase and the skin to become redder.

Before participants entered the tight MRI tube, researchers told them that other volunteers would also watch their singing performance, hoping that might make them more embarrassed.

While undergoing the MRI, participants watched a video of themselves singing and a video of another participant singing on a screen above them. They wore headphones to block the loud beeping noises the machine produced.

“We didn’t know if we would really be able to evoke any kind of blushing in a very small, dark room where there’s no audience,” Nikolić said.

But researchers found that many participants’ cheek temperature increased by about one degree while they watched the videos of themselves singing — an indication that they were blushing. When viewing videos of other participants singing, most of the volunteers didn’t blush, Nikolić said. The cerebellum was most active when participants watched themselves sing, leading researchers to believe they were most engaged then and blushed as a spontaneous reaction.

There’s still more to learn about blushing, Nikolić said. To better comprehend the behavior, she next plans to research blushing in young children who haven’t developed the cognitive skills to consider what other people think of them.