The role of trial tracking in rats' working memory

Abstract

The experiments reported in the present study tested whether decreasing intertrial intervals (ITIs) intensifies the disruptive effects of increasing retention intervals (RIs) in a delayed conditional discrimination by decreasing the animal's trial tracking accuracy (Cohen and Armstrong, 1996; Cohen and Roberts, 1996). Rats responded on a fixed ratio (FR) 1 or fixed interval (FI) 10-sec reinforcement schedule at a second light or tone stimulus, S2, when the first light or tone stimulus, S1, had signaled an FI 10-sec or FR 1 schedule, respectively. RIs between S1 and S2 were increased from 3 to 24 sec and never exceeded ITIs that were reduced from 24 to 6 sec. For some rats, the trials were separated from each other by extending the lever at S1 and retracting it at the end of S2 (ITI lever-retracted group). For other, control rats, the lever remained extended throughout the session (lever-extended group, Experiment 1) or was extended and retracted with the onset and offset of each stimulus (RI/ITI lever-retracted group, Experiment 2). The rats under all trial conditions learned to delay leverpressing on the FI 10-sec schedule. Latency to begin leverpressing on the FI 10-sec schedule declined as RIs were increased, but this effect was attenuated in the ITI lever-retracted groups in both experiments, as would be predicted by the trial tracking hypothesis. Decreasing ITIs from 24 to 6 sec intensified the disruptive effects of increasing RIs from 3 to 6 sec in the RI/ITI lever- retracted group (Experiment 2), as would be predicted by the trial tracking hypothesis.