The adaptive function of mood change.

It is useful to imagine an 'agonistic strategy set', containing the two alternative and mutually incompatible strategies of escalation and de-escalation. The strategy set is accessed by loss, threat or some other form of 'ranking stress'. It is further suggested that ranking stress is dealt with relatively independently at three levels of the brain/mind, so that an agonistic strategy set is deployed at each of the three levels. Normally, all three levels escalate or de-escalate in unison, but sometimes lower level de-escalation is associated with middle or higher level escalation, and then the resolution of agonistic situations is delayed and psychopathology may be recognized.