Evidence for timing in the midsession reversal task with rats.

The midsession reversal task is frequently used to study behavioral flexibility and decision strategies in animals. In a typical version of the task, subjects complete 80 trials in which they choose between two simultaneously presented stimuli, S1 and S2. During the first 40 trials, responses to S1 are reinforced, whereas responses to S2 are not. The contingencies then reverse and, from Trial 41 to 80, only responses to S2 are reinforced. In birds, performance in this task is often characterized by a strong preference for S1 on the first trials and for S2 on the last trials, with a gradual reversal of preference from S1 to S2 around the contingency-reversal trial. Anticipatory and perseverative errors at midsession suggest that the birds rely on elapsed time since the session began to reverse their preference. In contrast, rats tested in operant conditioning chambers typically show near-optimal performance with few errors, a pattern often interpreted as evidence that rats rely primarily on local reinforcement cues rather than temporal information. The present study investigated whether rats exclusively rely on local cues in the midsession reversal task or whether temporal information also contributes to the decision process. Two groups of rats were trained in the standard task with different intertrial intervals: 5 or 10 s. During acquisition, both groups displayed similar learning rates and near-optimal steady-state performance with minimal anticipatory or perseverative errors. However, when the intertrial interval changed in probe sessions, the pattern of choices was affected also by the temporal midpoint experienced during training. These results suggest that rats rely on a mixed strategy that combines local response-outcome cues from the last trial(s) with global time cues. Hence, temporal control may be present even when it is not expressed during standard training sessions. (PsycInfo Database Record (c) 2026 APA, all rights reserved).