Acquisition of the classically conditioned eyeblink response in humans over the life span.

Human subjects ranging in age from 18 to 85 years underwent classical conditioning of the eyeblink response to a tone conditioned stimulus (CS) and an air-puff unconditioned stimulus (UCS). There was a decline in percentage of conditioned responses with age. This decline was most noticeable in subjects over age 50. These conditioning deficits were not due to age-related changes in sensitivity to the tone CS or the air-puff UCS, nor could the conditioning deficits be attributed to an age-related decline in general cognitive abilities or to changes in spontaneous blink rates. The results are discussed in terms of using the classically conditioned eyeblink in humans in conjunction with the classically conditioned nictitating membrane response in rabbits as a model system for studying the neurobiology of age-related conditioning deficits.