Developmental constraints on the expression of behavioral and heart-rate orienting responses: I. The role of cardiosomatic coupling

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Abstract
The ontogeny of behavioral and heart‐rate orienting responses to a novel olfactory stimulus was examined in three experiments. The results of Experiment 1 demonstrated that behavioral responses to the olfactory stimulus were observed as early as early as Day 1, although heart‐rate deceleration in response to the stimulus was not observed until Day 9. In Experiment 2, bradycardia was observed in 6‐day‐old pups if stimulus‐elicited motor activity was reduced with haloperidol. Thus, the developmental asynchrony in the expression of behavioral and heart‐rate orienting responses was due, at least in part, to cardiosomatic coupling in the very young animal. The results of Experiment 3 demonstrated that although cardiosomatic coupling interferes with the expression of the heart‐rate orienting response very early in development, it has increasingly less impact over the course of the preweaning period.