People differ in what they experience as stressful and to what extent. We define a variable-stress threshold (sigma)-that links the hypothalamo-pituitary-adrenocortical (HPA) axis and the memory system in a feedback mechanism. Current sigma dictates the intensity of a stimulus that turns the stress response on. On the other hand, each jump of the HPA axis helps long-term registration of the stressful event via concentration changes of some of its products, consequently changing the value of sigma for future stressors. After the action of a strong exterior stressor, the new stressful memory acts as an internal source of stress. We assume that its intensity decreases with the rate of processing the stressful information. This process is characterized by a time parameter tau. Both sigma and tau are individual: They depend on personality traits, genetic as well as acquired. The mathematical model presented here simulates the feedback mechanism between the HPA axis and the memory system involved in stress reaction
