Conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response: US intensity effects.

Conditioning-specific reflex modification (CRM) of the rabbit's nictitating membrane response (NMR) describes changes in responding to an unconditioned stimulus (US) when the rabbit is tested in the absence of the conditioned stimulus. Specifically, after at least 3 days of tone-electrical stimulation pairings, responses to the US increase in size, especially at intensities weaker than the training intensity. CRM is similar to classical conditioning in that it is a function of the strength of conditioning, it can be extinguished, and it can be generalized from one stimulus to another. To compare CRM and classical conditioning further, we conducted three experiments to examine the effects of US intensity (1.0, 2.0, and 4.0 mA) on CRM. CRM was weak following conditioning with 1.0 mA and extremely strong following conditioning with 2.0 mA and 4.0 mA. The data suggest that CRM is a function of US intensity and have implications for posttraumatic stress disorder, a disorder potentially modeled by CRM.