Figure 4.

Chronic stress response. If the stressor is above a certain intensity or duration, the sympathetic response is more intense; if there is an inadequate defensive response, the system as a whole may fail to reset to normal functioning, remaining “tuned” to excess sympathetic and deficient parasympathetic activation. This state may persist indefinitely, giving rise to a state of “chronic stress,” where the system responds inappropriately to environmental challenge with excess activation. Note that this is not “allostatic wear and tear,” but an altered (dys-)functional state; such a chronic state is a major contributor to allostatic over-load. Through appropriate intervention, the system can be returned to a normalized, fully functional state; but without such intervention the dysfunctional state may last indefinitely.