Were scientists to concoct an experiment that was all but guaranteed to unleash full-on, cheek-reddening embarrassment, then filming adolescents singing Let It Go from Frozen and playing back their performance might well do the job. And so to researchers at the University of Amsterdam who invited dozens of young volunteers into the lab before breaking the news as to what was required. In front of a camera, and without the benefit of a shot or two, they were asked to sing the Arendelle anthem or another choice track, before they and others watched the rendition back from inside a brain scanner. Through such pre-meditated mortification, and measurements from temperature sensors stuck to the participants’ cheeks, scientists hoped to uncover the signature of blushing in the brain, the neural activity underpinning what Darwin called “the most human of all expressions”. Psychologists speak of two broad theories when it comes to blushing. The one favoured by Darwin proposes that reddening cheeks come on when we consider how we must look to onlookers. The other suspects something simpler is afoot: a more spontaneous response to feeling exposed. “Is it just being in the social situation where you are exposed and centre of attention, and you feel the exposure, and attention from others,” said Dr Milica Nikolic, a psychologist and first author on the study. “Or is it more complex and that we start thinking about how we look and appear to other people?” After advertising for young people to take part in research that involved a “social task” and watching videos in a brain scanner, the scientists heard from more than 60 young people aged between 16 and 20. All but two were males, leading to a decision to focus purely on young women. On the first visit to the lab, each volunteer was asked to perform karaoke while being filmed. The songs were restricted to Let It go, Adele’s Hello, Mariah Carey’s All I Want For Christmas Is You and All The Things She Said by t.A.T.u – tracks that are deemed hard to do well and thus were contenders to cause the maximum embarrassment. Cue awkward smiles, arm scratching and some justifiably nervous warbling. A week later, the volunteers were back in the lab. This time, they watched their performance, along with those of others, while lying in a brain scanner. They were told others were watching their performance at the same time, a ruse designed to add to their embarrassment. People, as expected, blushed more readily watching themselves than others. But analysis of the brain scans revealed that the sudden reddening of the cheeks might not be triggered the way Darwin thought. Blushing went hand in hand with greater activity in the cerebellum, which the researchers link to emotional arousal, and signs in the visual cortex that people were paying close attention to their performance. Nothing in the scans suggested that people were thinking about how others might judge them, the researchers found. “Blushing can come simply from being exposed,” said Nikolic. “In that very short moment you maybe don’t think about how do I look and so on. I think it’s more automatic than the theory says.”