Delay classical conditioning in young and older rabbits: initial acquisition and retention at 12 and 18 months

Classical conditioning of the nictitating membrane-eyeblink response in young (7 months old) and older (36 months old) New Zealand white rabbits in a delay paradigm with a 400-ms conditioned stimulus-unconditioned stimulus interval was examined for initial acquisition and retention. Older animals required significantly more acquisition trials to reach learning criterion. Age differences in acquisition were temporary. Older rabbits responded at a level comparable to that of young rabbits such that total performance over the 630 trials of acquisition was not different. Rabbits in the explicitly unpaired control groups exhibited no age differences in unconditioned response amplitude or latency measures. Twelve- and 18-month retests demonstrated no significant age effects on retention. Patterns of retention differed between the age groups. Older rabbits required fewer trials to obtain the learning criterion at each phase of testing. Younger rabbits maintained a stable performance throughout training.