“Stress can also prevent extinction from taking place.53 This is thought to be due to the fact that stressful events release the hormone cortisol via the pituitary-adrenal system (see Chapter 3); this hormone has impairing effects on PFCVM function.54 Thus, the very factor needed to induce extinction—exposure to stressful threats—can prevent extinction. This is an argument against the use of flooding and related exposure procedures that elicit high levels of “fear.” However, the hormones released during stress that impair extinction have complex and sometimes opposing effects on different phases of learning (acquisition, memory consolidation, memory retrieval, extinction, and memory reconsolidation).”