We originally coined the term conditioning-specific reflex modification (CRM) to describe changes in the rabbit's nictitating membrane response (NMR) to an unconditioned stimulus (US) when the US was tested by itself after classical conditioning. Following pairings of a tone conditioned stimulus (CS) and electrodermal stimulation, NMRs to the US increased in size and peaked later, especially at intensities weaker than the training intensity. Post-traumatic stress disorder [PTSD] is a psychological disorder resulting from exposure to a traumatic event. The symptoms associated with PTSD include persistent re-experiencing of the traumatic event, persistent avoidance of stimuli associated with the trauma, numbing of general responsiveness, and persistent symptoms of increased arousal. One of the hallmarks of PTSD is intense psychological distress and/or physiological reactivity to cues that symbolize or resemble an aspect of the traumatic event. This learning-related aspect of PTSD has some similarities to CRM. Like a Vietnam veteran who "hits the deck" when he hears a car backfire, our rabbits now blink to a mild electrical stimulus as if it were a strong stimulus. We would argue that the backfire is a weak "US" rather than a "CS."

Figure shows simple reflex responses are increased in size and become more complex after learning.