Perseverative cognition is defined as “the repeated or chronic activation of the cognitive representation of one or more psychological stressors” (Brosschot, Gerin, & Thayer, 2006). Stressful events, or stressors, can make people “linger on” mentally. Humans, unlike animals, can make mental representations of stressors, long before and long after these events occur or are believed to occur. This continued cognitive representation of stressful events, before or after their occurrence, and even regardless of their actual occurrence, is called perseverative cognition. It can take the form of worry, rumination, angry brooding, etc., but also, for example, as mind wandering about negative topics. Perseverative cognition appears to play a causal or sustaining role in several major psychopathologies (anxiety disorders, depression, post-traumatic disorder) (Watkins, 2008) – indeed, worry is the hallmark of...