Heart rate during conditioning in humans: Effects of UCS intensity, vagal blockade, and adrenergic block of vasomotor activity.

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Abstract
Two experiments concerned with the influence of the vagal and sympathetic innervations of the heart and of peripheral reflex mechanisms are reported on the deceleration of heart rate observed on test trials during classical conditioning in human Ss. An increase in vagal restraint was observed to be the basis of the deceleratory response, which in turn masks the manifestation of sympathetic acceleratory effects. The latter were only observed when the vagus was pharmacologically blocked and when a very intense UCS (unconditioned stimulus) was used. When the conditioned pressor responses were blocked pharmacologically, as evaluated by direct recordings of arterial blood pressure, the deceleratory response was not changed, indicating that the peripheral homeostatic reflex mechanisms are not the basis for this response and that it is likely a conditioned response.

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