Startle Potentiation and Heart Rate as Affected by Fear and Hunger

Abstract

In a widely cited, unpublished study, abstracted at length herein, Meryman in 1952 reported that the acoustic startle response of the rat was potentiated by conditioned fear, by food deprivation, and summatively by both combined. Whereas others have verified the action of fear on startle, only scattered support has been obtained for the conclusion that startle can be potentiated by an appetitive variable. Because of the significance of this matter for general drive theory, further study is imperative. The present experiment, a replication and extension of Meryman's, was guided by a design in which two levels of fear and two of food deprivation were combined factorially. Two groups of rats, one deprived for 40 hr. and one for 1 hr., were shocked in a stabilimeter chamber to condition fear to the cues of that situation. Two other, nonfearful groups, one of which was deprived for 40 hr. and the other for 1 hr., were never shocked in the stabilimeter. Instead, they were shocked in a distinctively different chamber to control for amount of aversive stimulation across groups. Results provided by measurements of startle amplitude coincided with Meryman's in that response magnitudes increased over conditioning trials for the fearful animals but not for the controls and in that rats which were both fearful and deprived exhibited stronger reactions than fearful-only or deprived-only subjects. However, the appetitive variable alone did not exert a potentiating effect. Heart-rate recordings provided marginal evidence for the conditioning of fear. Our results and Meryman's, as well as the discrepancies between them, are explained as due to the depressing effect of near-satiation on the capacity of fear to potentiate startle.