Patterns of reflex action, their autonomic components, and their behavioral significance.

This is a discussion of the evidence that autonomic system reflexes are invariably triggered by stimuli that evoke both simple and complex somatic reflexes. Stimuli not only initiate reverberatory activity but sequences of reinforcements from higher centers. Reflexes come in chains, one reaction triggering another. Reflex actions are patterned, and these patterns are appropriate to the behavioral requirement indicated by stimuli. Reciprocal action produces a powerful braking or stimulatory action. Coactivation or synergic action of autonomic "antagonists" also occurs and can effect a greater cardiac output in certain vascular reflexes that can sympathetic action alone. Coactivation of vagus and sympathetic fibers occurring in reflex action or resulting from stimulation of specific areas in the hypothalamus has a physiologic importance to attainment of maximal cardiac function. Finally, two additional suggestions are made: (1) that the rhythmic reflex feedback discharge of the vagus from the baroreceptors aids in maintaining the regularity of cardiac rhythm as by interaction of oscillators and (2) that the autonomic system, due to its early and often conditioned response, can be determinative as well as modulatory and supportive of behavior.