Parasympathetic Over-activation
Cannon believed that extreme emotional stress could be explained in terms of degree of sympathetic-adrenal excitation. However, an experiment performed by Curt Richter (1957) responded to Cannon's challenge with an animal model. Richter placed pre-stressed rats in a closed turbulent water. the latency to drowning was recorded. Most domestic lab rats lasted for hours while unexpectedly all of the wild rats died within 15 minutes. Richter monitored heart rate and determined whether the heart was in systole or diastole after death. He found out that heart rate slowed down prior to death and the heart was engaged with blood reflecting a state of diastole. This contradicted Cannons proposal that sympathetic adrenal over-activation is the result of death since a sympathetic over-arousal would increase both heart rate and blood pressure to severe degrees. Richter interpreted this that the rats died as a result of Vagus death, direct result of over stimulation of parasympathetic nervous system. The lethal Vagal effect was the psychological state of hopelessness.
Sudden prolonged immobility or faked death is an adaptive response exhibited by many mammalian species. Hofer(1970) demonstrated that several rodent species when threatened exhibited an immobility that was accompanied by a very low heart rate. For some of the rodents that heart rate reached bellow 50% of the baseline. Hofer distinguished between prolonged immobility and faked death phenomenon. Unlike the behavior of "hopelessness" described by Richter, the death-faking occurred with a sudden motor collapse during active struggling. Hofer interpreted the fear-inducing slowing of heart rate as a Vagal phenomenon.
This data suggests that Vagus contributes to severe emotional states and may be related to emotional states of immobilization, such as extreme terror. Unfortunately, this immobilization technique is potentially life-threatening for mammals(but not for reptiles). Mammals would undergo states of Bradycardia or Hypoxia as an over-activation of parasympathetic Vagus system. The oxygen-hungry mammal is drained of oxygen and dies.
Read more about this topic: Voodoo Death