Abstract
ABSTRACT
An experimental group of 5 rabbits received 5 acquisition sessions during which repeated presentation of a 550 Hz tone for 10 sec as the conditioned stimulus (CS) was always followed immediately by 25 pulse per sec, 10 sec train‐duration stimulation of the posterior lateral hypothalamus as the unconditioned stimulus (US). A control group of 5 rabbits received random presentations of the CS and US. The unconditioned responses (URs) to intracranial stimulation consisted of tachycardia and a depressor response; conditioned responses (CRs) consisted of depressor responses unaccompanied by systematic changes in heart rate. Neither systematic heart rate nor blood pressure responses occurred to the CS in the control group.
The present results contrast with those of previous studies in rabbits in which higher frequency, shorter pulse‐train hypothalamic stimulation as US induced a pressor response and reflexive bradycardia as URs, and bradycardia unaccompanied by blood pressure changes as CRs. It is concluded that hypothalamic stimulation as US permits more than one cardiovascular response pattern to be studied under controlled conditions during classical conditioning.
