Temporal discounting of aversive consequences in rats

Previous research has extensively evaluated the impact of delay on the value of positive reinforcers, but the study of its impact on the value of aversive consequences is scarce. The present study employed a modification of Evenden and Ryan's procedure (1996, Psychopharmacology, 128(2), 161-170) to obtain data on temporal discounting of an aversive consequence, with rats as experimental subjects. In the first phase of the procedure, rats chose between one-pellet and four-pellet alternatives; when subjects developed preference for the larger-amount alternative, a shock was added to it, resulting in a loss of preference. In the first experimental condition, the delay to shock was progressively increased within each session from zero to 40 s (ascending delays), which resulted in a recovery of the preference for the larger-amount + shock alternative as the delay to shock was increased. In a subsequent condition (descending delays) the delay to shock was progressively decreased within each session, from 40 to 0 s. In both conditions, the preference for the smaller-amount no-shock alternative was well described by a hyperbolic function. The order of presentation of the delays within the session, ascending or descending, did not alter the relationship between preference and delay to shock. The temporal discounting curve obtained in the present study could represent a baseline for analyzing the impact that diverse environmental and pharmacological variables have on the temporal discounting of aversive consequences.