A microexpression is a facial expression that only lasts for a short moment. It is the innate result of a voluntary and an involuntary emotional response occurring simultaneously and conflicting with one another, and occurs when the amygdala responds appropriately to the stimuli that the individual experiences and the individual wishes to conceal this specific emotion. This results in the individual very briefly displaying their true emotions followed by a false emotional reaction.

Paul Ekman is an American psychologist and professor emeritus at the University of California, San Francisco who is a pioneer in the study of emotions and their relation to facial expressions. He was ranked 59th out of the 100 most cited psychologists of the twentieth century. Ekman conducted seminal research on the specific biological correlations of specific emotions, attempting to demonstrate the universality and discreteness of emotions in a Darwinian approach.