 Assuming (as most emotion theorists do) that the cardiovascular reactivity sparked by certain negative emotions prepares the body for specific actions, the broaden-and-build theory suggests that positive emotions can speed recovery from—or undo—this cardiovascular reactivity and return the body to mid-range levels of activation suitable for pursuing a wider range of behavioral options.According to this view, positive emotions have a unique ability to down-regulate lingering negative emotions and the psychological and physiological states they generate.In one of the studies, they gave participants an acute stressor – the possibility of giving a public speech.