A mathematical model of stress reaction: Individual differences in threshold and duration

People differ in what they experience as stressful and to what extent. We d efine a variable-stress threshold (sigma)-that links the hypothalamo-pituit ary-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 i ts products, consequently changing the value of sigma for future stressors. After the action of a strong exterior stressor, the new stressful memory a cts as an internal source of stress. We assume that its intensity decreases with the rate of processing the stressful information. This process is cha racterized by a time parameter tau. Both sigma and tau are individual: They depend on personality traits, genetic as well as acquired. The mathematica l model presented here simulates the feedback mechanism between the HPA axi s and the memory system involved in stress reaction.