No abstract

To evaluate the effectiveness of prior discrimination training on subsequent heart-rate (HR) shaping under curare, 30 subjects were divided into three groups on the basis of amount of discrimination training (0, 2, and 4 hr.). These rats were then curarized and trained to increase or decrease HR with electrical stimulation of the brain (ESB) as reward. Results indicated that the animals did learn to produce significant changes in HR in the reinforced direction, although amount of discrimination pretraining had no effect on the magnitude of these changes.

Heart rate of curarized and non‐curarized rats was recorded while both groups were exposed to classical conditioning procedures with tone as the conditional stimulus (CS) and shock as the unconditional stimulus (UCS). The unconditional HR response of curarized animals to the tone was significantly greater than that of the non‐curarized animals, while the HR response to shock of the curarized animals was significantly less than that of the non‐curarized group. Both groups showed evidence of conditioning over 30 conditioning trials.

In order to determine whether parasympathetio stimulation given coincidentally with electric shock in a "fear-conditioning" situation would alter later performance on an avoidance conditioning task, one group of 10 subjects was implanted with a small chronic electrode around the cervical vagus. During preconditioning, consisting of 8 trials of tone followed by inescapable shock, one group of animals received stimulation of the vagus at the time foot shock was delivered. During subsequent avoidance conditioning, these subjects performed the avoidance task significantly better than subjects that received the same preconditioning without vagal stimulation and as well as subjects that had received no preconditioning shock trials.Recently DiCara and Weiss (1969) evaluated the effects of heart rate (HR) increase or decrease produced in curarized rats by avoidance training on the learning of a later skeletal avoidance response. They found that subjects reinforced for HR decrease in the pretraining phase were not significantly different from naive control subjects, while subjects reinforced for HR increase showed "freezing" behavior and generally failed to learn the avoidance response. The performance of the HR-increase group suggests that fear was transferred from the HR task to the skeletal avoidance task and that it was specific to the conditioned stimulus (OS). Subjects in this group "froze" to the tonal CS and could not learn a one-way avoidance task. The only known difference between these groups was the direction in which subjects learned to alter HR. The goal of the present study was to see if similar effects would be obtained when HR decrease was produced by a different method and in a different pretraining situation. In the present study a chronic electrode for stimulating the vagus nerve was used to alter autonomic reactivity during pretraining, which consisted of 8 trials of tone followed by inescapable grid shock in one group of subjects. Their performance on a later skeletally mediated 1 Requests for reprints should be sent to John

An electrode suitable for chronic implantation around the cervical vagus with lead wires attached to a female connector head piece was developed. Electrical stimulation through the electrode effectively produced a heart rate decrease, an indicator of effective vagal stimulation, in approximately 75 of the subjects implanted for a 14 day test period.