Age-related disruption of trace but not delay classical conditioning of the rabbit's nictitating membrane response

Young (6 months of age) and old (36-60 months) New Zealand albino rabbits underwent classical conditioning of the nictitating membrane response in either a delay conditioning (Experiment 1) or a trace conditioning (Experiment 2) paradigm. There was no difference between old and young animals in acquisition of the conditioned response in the delay paradigm, nor were there any age-related differences in generalization to the tone conditioned stimulus (CS) or in sensitivity to the tone CS or eye shock unconditioned stimulus. In the trace conditioning paradigm, however, old animals acquired the conditioned response significantly more slowly than young rabbits. Because the same stimulus parameters and the same response were used in both experiments, it is unlikely that age-related differences in trace conditioning were due to stimulus sensitivity, motivation, or fatigue. The results are discussed in terms of how brain changes that accompany aging could differentially affect these two types of classical conditioning.