(1998) characterize anxiety as dysfunction in learning negative contingencies between a cue and an aversive stimulus. We propose that problems in learning that a cue is a negative predictor of a reward are crucial for the manifestation of impulsive behavior.
When exposed to fear conditioning protocols, animals acquire fear memory through the association between conditioned stimuli--a tone, a smell, or a context--with an unconditioned aversive stimulus, usually a foot shock.
If this impact was not present in the "staying" condition, it is likely that differences were not noticeable because of the impact of the aversive stimulus in the rats, so that generally the subjects didn't make mistakes.
Conditioned fear in vertebrates such as rodents is often brought about by pairing an aversive stimulus (the US)--for example, an electric shock-- with a neutral stimulus (the CS)--for example, a tone (see Maren, 2001).