SLC6A4 and major depressive disorder: Although the behavioral response to ambiguous feedback is likely to differ in humans and rodents (increased negative feedback sensitivity vs. increased post-reinforcement latency), intolerance of uncertainty is found in major depression and anxiety disorders (Carleton et al., 2012; Boswell et al., 2013) and recent evidence indicates that the 5-HTTLPR also influences decision making under ambiguous circumstances (He et al., 2010; Stoltenberg and Vandever, 2010; Stoltenberg et al., 2011).