Famous Russian scientist (physician and psychiatrist) and Nobel Prize winner Ivan Pavlov -- famous for his experiments with ringing bells, feeding time and dogs that evoked the characteristic "Pavlovian response" -- also had some things to say about PTSD. Bessel van der Kolk, M.D., a Harvard-trained psychiatrist, writing in his scientific paper, "The Body Keeps the Score: Memory and the Evolving Psychobiology of Post Traumatic Stress," mentions that Pavlov thought that "individual differences in temperament account for the diversity of long-term adaptations to trauma." Interesting!
Editor's Note: The item van der Kolk appears to be citing is Pavlov IP. Edited and translated by GV Anrep. "Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex." New York: Dover Publications (1926).