Form and characteristics of the cardiovascular conditional response in Rhesus monkeys

Three Rhesus monkeys restrained in primate chairs were exposed to several Pavlovian control procedures, followed by 13 sessions of cardiac conditioning under a delay paradigm. The conditional stimulus (CS) was a vertical line and the unconditional stimulus (US) was electric foot shock. Heart rate (HR) was analyzed in successive fivesecond intervals beginning five seconds before CS onset. The major finding was that the conditional response was consistently biphasic and consisted of an initial acceleration followed by deceleration toward the baseline, but rarely reaching it before onset of US. The subjects differed in magnitude of acceleration and subsequent deceleration as well as the location of the maximum rate in the CS-US interval. A breakdown of trials on the basis of the pre-CS HR revealed that the magnitude of effect was inversely related to the pre-CS rate.