Sometimes a traumatic incident can trigger an enduring response of fear whenever the incident is recalled, even indirectly. A car backfiring, for instance, can set off an emotional response in a combat veteran if the loud noise becomes associated in his mind with a wartime experience.

有些时候，只要大脑中回忆起创伤性事件，即便是间接的回忆，也会引发人体持久的恐惧反应。比如，汽车爆胎会让退伍老兵产生情绪化的反应，只要他的脑子将这声巨响同战争中的某次经历联系在了一起。