Conditioned Reflex Reactions in High-Impulsivity Rats Are Weaker than Those in Low-Impulsivity Animals

The delay discounting procedure was used to classify rats into high-impulsivity (preferring low-value immediate food reinforcement) and low-impulsivity (choosing a high-value reinforcement with a 5-sec delay), as well as ambivalent animals, which did not display any preference for reinforcement choice. In high-impulsivity rats, the conditioned fear reaction assessed in terms of freezing reactions was less intense than in low-impulsivity and ambivalent rats. Between-group differences were apparent at the training stage and on testing the reflex 24 h after training. Differences were seen both on exposure to the signal stimulus (a sound) and on exploration of the context. Extinction of the conditioned reflex fear reaction in high-impulsivity rats occurred more quickly than in low-impulsivity and ambivalent animals. Pain reaction thresholds (twitching and jumping) were no different in the three groups of animals. The results are assessed in relation to concepts of the functional and dysfunctional forms of impulsivity and their corresponding manifestations of conditioned reflex fear and negative affective disorders.