Emotions are feelings that have physiological and cognitive elements and influence behavior. They prepare us for action, shape future behavior, and help us interact effectively with others. There are several theories about the roots of emotions, including the James-Lange theory that emotions are reactions to bodily events, the Cannon-Bard theory that physiological arousal and emotions occur simultaneously, and the Schachter-Singer theory that emotions are determined by physiological arousal and environmental cues. The amygdala plays a role in linking emotion-producing stimuli to later recall. While facial expressions of emotion may be universal, display rules govern appropriate emotional expression. The six primary emotions are happiness, anger, sadness, surprise, disgust, and fear.