Neural Substrates Underlying Learning-Related Changes of the Unconditioned Fear Response
Three groups of subjects, viz. low trait anxious (LA), high trait anxious (HA) and neurotic patients (PAT) recieved a series of warned unpleasant auditory stimuli. The expectation that the warned stimuli would evoke smaller accelerative heart rate responses than the unwarned ones was not confirmed. On the contrary, the responses to the warned stimuli stimuli were larger than to the unwarned stimuli. Evidence was provided for the idea that homeostatic mechanisms were, at least in part, responsible for this result, though the possibility that even homeostatic heart rate changes can have psychologically relevant effects on central structures was not excluded. Neither the responses during the ISI nor the responses to the unpleasant stimuli (UCS) differed between groups although the response in the IS was in the predicted direction, i.e. a stronger initial acceleration in the LA group as compared to the HA and PAT groups. It was further suggested that the difficulty separating homeostatic effects from changes in sensitivity of the organism makes the operationalization of preception in terms of UCR amplitude of heart rate questionable.