The touchscreen operant platform for assessing executive function in rats and mice

Abstract

This protocol details a subset of assays developed within the touchscreen platform to measure various aspects of executive function in rodents. Three main procedures are included: extinction, measuring the rate and extent of curtailing a response that was previously, but is no longer, associated with reward; reversal learning, measuring the rate and extent of switching a response toward a visual stimulus that was previously not, but has become, associated with reward (and away from a visual stimulus that was previously, but is no longer, rewarded); and the 5-choice serial reaction time (5-CSRT) task, gauging the ability to selectively detect and appropriately respond to briefly presented, spatially unpredictable visual stimuli. These protocols were designed to assess both complementary and overlapping constructs including selective and divided visual attention, inhibitory control, flexibility, impulsivity and compulsivity. The procedures comprise part of a wider touchscreen test battery assessing cognition in rodents with high potential for translation to human studies.

Figure 1. Flowchart overview of pretraining stages 2-5.

Stage 2: A visual stimulus is presented in one of the response windows. If not touched, stimulus offset occurs after 30 s and a reward is delivered. If touched, offset is immediate and a triple reward is delivered. After reward collection and an ITI period, the next stimulus is presented in a new trial. Stage 3: Proceeds as in Stage 2, but the stimulus remains on the touchscreen until touched. Animals to be tested on Extinction can proceed directly to the Extinction procedure after reaching criterion on Stage 3. Stage 4: Proceeds as in Stage 3, but the animal must enter and exit the magazine after the ITI to initiate the next trial. Stage 5: Proceeds as in Stage 4, but touches to blank response windows (when there is a stimulus on the screen) are discouraged with a time out. Following this and the ITI the next trial may be initiated, but in pretraining for the majority of tasks this is a CT in which the previous stimulus is represented, rather than a new trial. Note that CTs are not given in Stage 5 of pretraining for the 5-CSRT. The labels in italics indicate steps in which the animal is required to perform an action.

Figure 2. Extinction task.

A: Schematic of a three-hole mask used in the Extinction paradigm. B: Flowchart overview of acquisition learning phase. Following initiation, a solid white square stimulus is presented at a central location on the touchscreen. When the subject touches the stimulus, a reward is delivered, and after reward collection and an ITI, a new trial may be initiated. The labels in italics indicate steps in which the animal is required to perform an action. C: Flowchart overview of extinction learning phase. Each trial begins with a 10 s ITI, after which the single, solid white square stimulus is presented on the touchscreen. The subject is not required to initiate the trial. If the subject either touches the stimulus (response) or does not touch the stimulus within a 10 s duration (omission), the stimulus is removed and the 10 s ITI leading to the next trial is initiated. No rewards or conditioned reinforcers (e.g., traylight or tone associated with reward delivery) are delivered during the extinction phase. The labels in italics indicate steps in which the animal is required to perform an action. D: Representative data of C57BL/6J mice using a 2-choice acquisition and extinction procedure showing the typical number of sessions to criterion (data replotted from ). E: Representative data from the same mice showing the time course of response extinction. Data are presented as means with error bars indicating S.E.M.

Figure 3. Reversal Learning task.

A: Schematic of a two window mask and stimuli used in the Reversal Learning paradigm. B: Flowchart overview of the Reversal Learning procedure. Following initiation, a pair of stimuli (CS+, CS−) is presented on the screen, in pseudorandom locations. Correct responses (to CS+) are rewarded, and after reward collection and an ITI, a new trial may be initiated. Incorrect responses (to CS−) are discouraged with a time out, then after an ITI and initiation the previous trial type is represented (a correction trial). The correction trial loop will continue until a correct response is made. The labels in italics indicate steps in which the animal is required to perform an action. C: Spider versus plane stimuli typically used for Visual Discrimination and Reversal Learning in rats (reproduced from with permission). D: Horizontal versus vertical pattern stimuli which rats acquire more readily. E: Typical Reversal Learning performance in rats (n = 10, with a history of Object-Location Paired Associates Learning and Trial-Unique Nonmatching-to-Location training) using “castle” versus “face” photographic stimuli (C.A. Oomen, unpublished results). F: Typical Reversal Learning performance in mice (n = 17, of mixed background (approximately 1:15 CBA/ca:C57BL/6J), using “marble” versus “fan” stimuli (A.E.H., unpublished results). Data are presented as mean +/− S.E.M.

Figure 4. 5-Choice Serial Reaction Time (5-CSRT) task.

A: Schematic of a five-hole mask used in the 5-CSRT paradigm. B: Flowchart overview of the 5-CSRT task. A trial is initiated when the subject enters and withdraws its head from the illuminated magazine. After a 5 s delay, a white square stimulus is briefly presented in one of the five response windows. Touching the white-square location either when the stimulus is present (or during a short subsequent limited-hold period) is recorded as a correct trial and rewarded. Collection of reward initates a 5 s ITI. A response in any other response window is recorded as an incorrect trial, and results in a time out period, before the beginning of the 5s ITI. Failure to respond at the screen during the stimulus presentation or the limited-hold period is recorded as an omission and also leads to a time out. Response(s) before the onset of the stimulus is recorded as a premature response, and lead to a time out, but premature trials do not contribute to the session trial count. After the ITI has elapsed, the magazine is illuminated and the subject can initate another trial. C and D: Representative data illustrating the dependence of response accuracy and omission, respectively, on stimulus duration in adult C57Bl/6J mice (S. Nilsson, L Saksida, T Bussey, unpublished data). Data are presented as mean +/− S.E.M.

Figure 5. Annotated photographs of a Campden Instruments rat touchscreen chamber.

(1) Touchscreen, (2) black plastic mask covering touchscreen except for response windows, (3) black Perspex walls, (4) pellet dispenser (optional), (5) infrared beam assembly, (6) houselight positioned above chamber, (7) infrared camera positioned above chamber, (8) tone and click generator, (9) sound/light-attenuating box with ventilation fan fitted.