It has been suggested that vertebrate freezing and tonic immobility (TI) represent the antecedents of human emotional vasovagal syncope. When a prey detects an approaching predator, it suddenly interrupts its ongoing activity and behaves according to the predator's distance. A prey enters TI when the fight or flight reaction is not feasible and the animal is captured. TI is defined as a post-contact, all or none, innate immobility reflex response that persists after the end of the prey-predator contact. In humans, vasovagal syncope, a reversible adaptive response frequently associated with fainting, occurs in response to emergency conditions such as strong emotions, orthostatic stress, anoxia, visceral pain and decrease in blood volume.

The aim of the present review is to dispute the hypothesis that human vasovagal syncope represents the evolution of the bradycardia observed during freezing in a prey-predator condition in other vertebrates. The hypothesis does not take into account three crucial issues: 1) freezing and TI are defence responses which differ from each other in behavioural, cardiovascular and neurophysiological correlates; 2) the initial phase of vasovagal syncope is associated with tachycardia, whereas freezing is associated with a sudden fast-developing bradycardia; 3) the second phase of vasovagal syncope terminates with a blood pressure collapse, whereas blood pressure levels remain at basal levels during both freezing and TI.

有人提出，脊椎动物冻结和强直不动 (TI) 代表了人类情绪性血管迷走性晕厥的前因。当猎物发现有接近的捕食者时，它会突然中断其正在进行的活动，并根据捕食者的距离采取行动。当战斗或逃跑反应不可行并且动物被捕获时，猎物进入 TI。TI 被定义为在猎物-捕食者接触结束后持续存在的接触后、全部或无、先天不动反射反应。在人类中，血管迷走性晕厥是一种经常与昏厥相关的可逆适应性反应，它是在应对紧急情况时发生的，例如强烈的情绪、直立性压力、缺氧、内脏疼痛和血容量减少。

本综述的目的是质疑人类血管迷走性晕厥代表其他脊椎动物在冷冻期间观察到的心动过缓演变的假设。该假设没有考虑三个关键问题：1) 冻结和 TI 是防御反应，它们在行为、心血管和神经生理学相关方面彼此不同；2）血管迷走性晕厥的初始阶段与心动过速有关，而冻结与突然快速发展的心动过缓有关；3) 血管迷走性晕厥的第二阶段以血压崩溃结束，而在冷冻和 TI 期间血压水平保持在基础水平。