Air puff versus shock unconditioned stimuli in rabbit heart rate conditioning.

The present study examined whether corneal air puff can be used as an unconditioned stimulus to elicit reliable classically conditioned heart rate (HR) responses in rabbits. The conditioned and unconditioned HR responses were assessed during Pavlovian conditioning with different intensities of paraorbital shock (2.7, 1.2, or 0.5 mA) or corneal air puff (18.3, 5.9, or 2.2 N/cm2) unconditioned stimuli (UCSs). Each experimental group was given one acquisition session during which an acoustic conditioned stimulus was paired with either the high, medium, or low intensity of a shock or air puff UCS. The results suggest that: a) HR is reliably conditioned with a high-intensity air puff UCS, and with medium- or high-intensity paraorbital shock stimuli; and b) only UCSs that elicit a tachycardiac unconditioned HR response reliably support HR conditioning. It was concluded that either air puff or paraorbital shock can serve as an effective UCS for HR conditioned responses.