Autonomic Interactions in the Control of Heart Rate in the Monkey

Each of 5 monkeys ( Macaca mulatta ) was operantly conditioned to raise and to lower heart rate consistently and reliably. Following such training the animals were tested using autonomic blocking agents (methyl‐atropine bromide and 1‐propranolol) to characterize the autonomic mechanisms mediating such control. The results were: 1) In the undrugged animal the extent to which it decreases its heart rate over a 2048‐sec period is a linear function of the baseline heart rate; 2) A linear relationship between baseline heart rate and heart rate decrease also is present within the first 128 sec; 3) There is a less consistent relationship between baseline heart rate and change in heart rate when animals must increase heart rate; 4) Vagal blockade significantly attenuates the ability of most animals to increase heart rate, primarily by reducing their ability to produce large, relatively rapid increases; 5) Sympathetic blockade significantly attenuates the ability of most animals to increase heart rate both in terms of overall changes and in terms of large, relatively rapid responses; 6) Vagal blockade very significantly attenuates the ability of all animals to slow heart rate; 7) Sympathetic blockade facilitates the ability of most animals to slow heart rate. These findings show that both branches of the autonomic nervous system participate in the operant control of heart rate. The relative role of one branch or the other in a given experiment will depend upon the baseline conditions at the time of testing, and upon the requirements—i.e., raising or lowering of heart rate.