Cardiovascular responses as behavior

Exercise is a ubiquitous, biologically and clinically significant behavior. Although the somatomotor responses are generally regarded as ''behavior,'' the cardiovascular adjustments that accompany these responses are generally considered to be reflexes that are elicited by neurally mediated stimuli and metabolites arising from working muscles. We report experimental evidence that monkeys can be trained to exercise, to slow heart rate, and to combine these two skills. Furthermore, some animals will emit more physical work at slower heart rates (at comparable levels of cardiac output) and lower left ventricular work during the combined condition relative to an exercise-only condition. Thus, these findings show that the cardiovascular and somatomotor responses of exercise can be dissociated and that both sets of responses should be considered behaviors. Also included are results that show these animals can perform these behaviors during sympathetic or vagal blockade. These findings are further evidence that the cardiovascular adjustments to exercise are, in part, learned behaviors because they show that the behavior - attenuation of the tachycardia of exercise - is not a reflex that is specifically tied to any neuroeffector system; rather, this behavior is emitted to achieve a contingent reward, and the nervous system will use whatever mechanisms are available to attain that consequence.