Classical conditioning of heart rate and blood pressure in Macaca mulatta.

Classical delay conditioning of heart rate, and of systolic and diastolic blood pressures, was carried out in 16 rhesus monkeys. Blood pressure and inter-systolic interval were measured from an in-dwelling arterial catheter; recordings were taken prior to conditioned stimulus (CS) on each trial, during a 20 sec visual stimulus that filled the conditioned-unconditioned stimulus (CS-UCS) interval, and following UCS (a brief electric tail-shock). The heart rate response both to CS and to UCS was biphasic (acceleration followed by deceleration); the blood pressure response functions were more complex, and were different for the CS and post-UCS periods. Comparison of the patterns of cardiac and blood pressure responses on any trial indicates a possible sequence of baroreceptor reflex activity.