Is fear all in the mind? Experiments on twins who can't feel fear are suggesting that some emotions are experienced only after we become aware of changes to our body. Many studies have shown that the amygdalae – two almond-shaped regions near the centre of the brain – are crucial for feeling fear. People who have lost their amygdalae through brain injury or disease also lose the ability to feel fear. In 2013, Justin Feinstein at the University of Iowa in Iowa City and his colleagues managed to scare three "fearless" people – two female identical twins and a woman known as S.M., none of whom have amygdalae – by getting them to inhale carbon dioxide, making them choke.