A stimulus previously paired with an electric footshock increases the point of subjective equality in timing in rats (Rattus norvegicus)

Abstract

In the present study, we examined time perception in the seconds-to-minutes range, interval timing, using a stimulus previously paired with an electric footshock as a to-be-timed stimulus. Rats were trained on the temporal bisection task using a 1000-Hz tone as the to-betimed stimulus. In Experiment 1, rats were trained on a standard temporal bisection task and we got the psychophysical functions; in Experiment 2, we measured rats' stable switching behavior during the presentation of a to-be-timed stimulus. In detail, rats waited in front of one lever for a period of time (switch latency) and then switched to the other lever and remained in front of it. Following sufficient training, they received differential classical conditioning in which one pitch (conditioned stimulus; CS+) was paired with an electric footshock (unconditioned stimulus; US) while the other pitch (CS-) was presented alone using 652- or 1633-Hz tones as CSs. The rats were then tested in the bisection task using the CS+ and CS- as to-be-timed stimuli. We found that the value of the point of subjective equality (PSE; Experiment 1) or the median of switch latency (Experiment 2) in CS+ trials was higher than in CS- trials. This result suggests that the stimulus previously paired with an electric footshock increases the value of the PSE in rats.