A microexpression is the innate result of a voluntary and an involuntary emotional response occurring simultaneously and conflicting with one another. This occurs when the amygdala (the emotion center of the brain) 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. Human emotions are an unconscious bio-psycho-social reaction that derives from the amygdala and they typically last 0.5–4.0 seconds, although a microexpression will typically last less than 1/2 of a second. Unlike regular facial expressions it is either very difficult or virtually impossible to hide microexpression reactions. Microexpressions cannot be controlled as they happen in a fraction of a second, but it is possible to capture someone's expressions with a high speed camera and replay them at much slower speeds. Microexpressions express the seven universal emotions: disgust, anger, fear, sadness, happiness, contempt, and surprise. Nevertheless, in the 1990s, Paul Ekman expanded his list of emotions, including a range of positive and negative emotions not all of which are encoded in facial muscles. These emotions are amusement, embarrassment, anxiety, guilt, pride, relief, contentment, pleasure, and shame.