Pavlovian conditioning of the immune system.

In the classical Pavlovian conditioning paradigm, a stimulus that unconditionally elicits a physiological response is repeatedly paired with a neutral stimulus that does not elicit that same response. Eventually, the neutral stimulus becomes a conditioned stimulus in that it elicits the physiological response in the absence of an unconditioned stimulus. Here we summarize experiments in which Pavlovian conditioning has revealed an intimate relationship between the central nervous system and the immune system.