Vagal activity predicts eyeblink conditioning in human subjects.

A group of old (mean age 73 years) and young (mean age 19.8 years) human subjects received concomitant eyeblink and heart rate classical conditioning, in which a 1000 Hz tone was the conditioning stimulus and a corneal airpuff was the unconditioned stimulus. Fewer old than young subjects showed eyeblink conditioning and age greatly attenuated the magnitude of the brady-cardiac conditioned heart rate response. The heart rate conditioned response was also significantly smaller in the subjects who failed to show eyeblink conditioning regardless of age, suggesting a relationship between parasympathetic cardiac control and somatomotor learning. The power associated with the respiratory peak in the heart rate spectrum, which is vagal in origin, was also smaller in subjects that failed to show eyeblink conditioning, again suggesting a relationship between parasympathetic cardiac activity and motor learning.