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Delay Intolerance Task: Different Impact of Timeout Duration on Impulsive and Non-Impulsive Rats

The intolerance-to-delay (ID) task, classically used to measure behavioural impulsivity in rodent models, requires the setting of specific temporal constraints: daily session length, reward delay intervals, and duration of timeout, i.e. the period following food delivery during which responding is without scheduled consequences. Here we focus on the impact of the timeout (TO) interval, to ascertain whether it affects or not the perception of delays. As expected, individual differences in the preference for large-late vs small-soon rewards emerged, with the identification of two distinct rat subpopulations: one with a nearly horizontal curve (“non-impulsive”) and another with a very steep slope (“impulsive”). Noteworthy, the reaction to increasing delay length was affected by the TO duration, but only as a function of individual temperament. Interestingly, the use of extended timeout periods further decreased impulsive choice in already delay-tolerant rats. In conclusion, we demonstrate that TO is a key constraint of the ID task and therefore should be handled carefully. Author Keywords