Schematic representation of operant-based tests of impulsivity in rodents. Green arrows represent correct responses and outcomes, whereas red arrows denote incorrect responses and associated outcomes. Blue arrows denote outcomes associated following an omitted response. Adapted with permission from Dalley and Roiser (Dalley and Roiser, 2012). (A) The five-choice serial reaction time task (5CSRTT) requires animals to wait for a food-predictive light cue before carrying out the response. The trial is initiated when the animal enters the illuminated food magazine (panel 1) and, following a delay (5 seconds), one of five cue lights is briefly illuminated (panel 3). If subjects nose-poke in the corresponding aperture, they receive a food reward (green arrow, panel 3). Responses that are made prior to the presentation of the cue light (impulsive responses; panel 2), are incorrect (red arrow, panel 3) or are withheld (panel 4) are punished by a 5-second time out during which the house light is extinguished. (B) The stop-signal reaction time task requires subjects to withhold reinforced responding following presentation of a tone cue (stop signal). The task begins following entry into the food magazine (panel 1), after which the left lever is introduced into the arena (panel 2). Responding on this lever introduces the right ‘reward’ lever, which, if depressed during a go trial (no tone), results in delivery of a food reward (panel 3). During a stop trial (during which a tone is presented), responding on the right lever is punished by a time out. If no responses are made during a stop trial, a food reward is delivered (panel 4). Conversely, if no response is made during a go trial, this is punished by a time-out period. Impulsive individuals have difficulty inhibiting responses during stop trials. (C) The delay-discounting task requires subjects to choose between a small immediate food reward or a larger reward delivered following a delay. The tasks begins following entry into the food magazine (panel 1), after which animals are presented with two levers (panel 2): one provides a small immediate food reward (left lever) and the other a larger reward following a delay (right lever). Omitted responses (panel 3) are unrewarded. Impulsive individuals prefer the immediate over the delayed reward.