The 5-Choice Serial Reaction Time Task: A Task of Attention and Impulse Control for Rodents

Summary

This protocol describes the 5-choice serial reaction time task, which is an operant based task used to study attention and impulse control in rodents. Test day challenges, which are modifications of the standard task, increase flexibility of the task and can be combined with other manipulations to more fully characterize behavior.

Abstract

This protocol describes the 5-choice serial reaction time task, which is an operant based task used to study attention and impulse control in rodents. Test day challenges, modifications to the standard task, can be used to systematically tax the neural systems controlling either attention or impulse control. Importantly, these challenges have consistent effects on behavior across laboratories in intact animals and can reveal either enhancements or deficits in cognitive function that are not apparent when rats are only tested on the standard task. The variety of behavioral measures that are collected can be used to determine if other factors (i.e., sedation, motivation deficits, locomotor impairments) are contributing to changes in performance. The versatility of the 5CSRTT is further enhanced because it is amenable to combination with pharmacological, molecular, and genetic techniques.

Introduction

The 5-choice serial reaction time task (5CSRTT) was developed by Trevor Robbins and colleagues at the University of Cambridge in order to understand the behavioral deficits displayed by people diagnosed with attention deficit hyperactivity disorder (ADHD)^1,2. It is based upon continuous performance tasks used to study attention in humans³; with attention being defined as the ability to allocate and sustain the focus of cognitive resources on specific stimuli or information while ignoring other information⁴. Although the task was originally designed for use with rats^1,2, a mouse version has also been developed^5,6.

The basic 5CSRTT requires rats to scan a horizontal array of five apertures for the presentation of a brief light stimulus (cue) in one of the apertures; once the rat detects the stimulus it must nose poke in the illuminated aperture to receive a sugar pellet reward. Thus, the task requires rats to both divide their attention across the 5 spatially distinct apertures and to sustain attention until the stimulus is presented in a given trial and across multiple trials in a session^1,7. Attention is typically assessed by the accuracy of responses. Although the 5CSRTT was originally designed to assess attention, it is also used to assess impulsive behavior or response inhibition^1,7,8: the ability to withhold pre-potent or inappropriate responding⁹. During the task, rats must withhold responding for the duration of the inter trial interval (ITI) and only respond once the stimulus is presented in one of the apertures¹. Thus premature responses, those occurring during the ITI prior to stimulus presentation, provide a useful index of impulsive behavior.

The 5CSRTT is an incredibly flexible task—there are a number of modifications of the basic task (i.e., test day challenges) that can be implemented to more carefully examine how experimental manipulations affect behavior. For example, decreasing the stimulus duration or shortening the ITI are different mechanisms to increase the attentional load of the task and can be used to systematically assess subdomains of attention^1,7,10-12. In contrast, increasing the stimulus duration minimizes the attentional demands of the task; this can be used to determine if a manipulation interferes with the ability to execute the basic response requirements of the task¹². Increasing the duration of the ITI can be used to determine whether a particular manipulation affects impulsive responding^1,7,8,13-15. Moreover, using test day challenges, such as those just described, can reveal deficits¹⁰ or enhancements^16,17 of behavior that are not apparent in well trained rats tested using standard testing parameters.

Importantly, the 5CSRTT is amenable to combination with a number of different techniques; for example cognition has been investigated following lesions of discrete brain areas^10,18-20, or selective neurotransmitter depletions^2,21,22. Behavioral pharmacological investigations have used either systemic^16,17,23-28 or discrete intracranial administration of drugs^29-32. Moreover performance is easily assessed after acute^{12,16,17,29-32} and chronic drug administration^13,14,23,33. The effects of task performance on neurotransmitter release³⁴ and metabolic activity³⁵ in discrete brain areas have also been assessed. In addition, performance on the task can be used to separate rats into groups based on baseline attentional performance^30,31 or levels of impulsivity^15,32. Finally, with the advent of a mouse version of the 5CSRTT^5,6, the task has been used to investigate the genetic contributions to attention and impulse control^5,36-39.

Because the 5CSRTT assesses multiple cognitive functions simultaneously and is amenable to use in combination of a variety of pharmacological, molecular and genetic approaches it has been routinely used to assess cognitive dysfunction in the context of animal models of psychiatric and neurological disorders. For example, the 5CSRTT has been used to investigate the neurobiology underlying the cognitive disruptions in attention deficit hyperactivity disorder (ADHD)^37,40,41, schizophrenia^23,33,42, drug addiction^13,14,43-45, Alzheimer’s disease^18,39, Parkinson’s disease³⁶, and Huntington’s disease³⁷.

This protocol provides guidelines for training rats on the 5CSRTT. Because a number of performance measures can be collected, we describe how common patterns of results should be interpreted. In addition several common modifications to the basic protocol, the test day challenges, are described.

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Protocol

This procedure requires the use of animals; these procedures were approved by the Oberlin College Institutional Animal Care and Use committee and are in accordance with the Guide for the Care and Use of Laboratory Animals⁴⁶.

1. 5CSRTT Apparatus

1. A schematic of the 5CSRTT apparatus is provided in Figure 1.
   1. The 5CSRTT apparatus consists of an operant conditioning chamber (30.5 x 24.1 x 29.2 cm) with 2 Plexiglas sidewalls, and a stainless steel grid floor.
   2. The aluminum front wall is rounded and contains five nose poke apertures (2.5 x 2.2 x 2.2 cm each); each aperture is equipped with a light emitting diode (LED) and an infrared sensor capable of detecting the insertion of the rats’ nose.
   3. The aluminum back wall contains the food magazine; this is connected to a pellet dispenser and is equipped with an infrared sensor and a small incandescent light.
   4. An incandescent house light, capable of illuminating the entire chamber is affixed near the top of the back wall.
2. House the 5CSRTT apparatus within a ventilated, sound attenuated operant conditioning chamber.
3. Use a PC computer to control the operant chamber and to collect data.

2. Animal Housing and Preparation

1. The procedure requires use of experimental animals; obtain approval from the Institutional Animal Care and Use Committee (IACUC) prior to commencing any experiments.
2. House rats in pairs.
   1. Maintain rats on a 14:10 light/dark cycle (lights on at 7:00 am) in a room with a constant temperature of 22 ± 1 °C.
   2. Allow rats free access to water while in their home cages, but food restrict them.
   3. Food restrict rats to 85-90% of their free feeding weight two to five days prior to the start of magazine training and throughout 5CSRTT training and testing. Feed rats after daily training sessions and weigh them daily to ensure that they are gaining weight (~5 g/week).

3. 5CSRTT Procedure

1. General 5CSRTT Training Considerations
   1. Train rats at a standard time of day a minimum of 5 days per week; training occurs over many stages (see Table 1) and takes several weeks.
   2. Train and test rats in the same operant chamber (see sections 3.2-3.5 below); small deviations in the rats’ environment can affect their performance.
   3. At the end of each session clean all surfaces of the chamber with water containing the disinfectant sodium hypochlorite (or another disinfectant after consultation with your veterinarian).
2. Magazine Training
   1. Introduce sugar pellets (45 mg) to rats in their home cage prior to the first session. This minimizes neophobia and ensures rats will retrieve sugar pellets from the food magazine.
   2. Place rats in operant chamber (fans on) with aperture holes occluded. Allow rats to habituate to chamber for 5 min.
   3. Deliver sixty sugar pellets to magazine on either a fixed interval 20 sec (FI-20, day 1) schedule or a FI-30 schedule (day 2).
      Note: The houselight can remain illuminated for the duration of the session and the magazine light should be illuminated upon pellet delivery and can remain illuminated until the pellet is retrieved.
   4. At the end of the session note whether sugar pellets are consumed; continue training for at least 2 days or until all of the pellets are consumed.
3. 5CSRTT Training
   1. Figure 2 provides a schematic of a single 5CSRTT trial.
   2. Place each rat in an operant chamber with fans on. Allow rats to habituate to chamber for 5 min.
   3. At the end of the habituation period, illuminate the magazine light and deliver one sugar pellet. The first trial begins when this pellet is retrieved.
   4. Begin each trial with an inter trial interval (ITI) during which only the house light is illuminated. At the end of the ITI, pseudo randomly illuminate one of the aperture lights for the prescribed stimulus duration. Allow the rat time to respond to the stimulus presentation; the time the rat is allowed to respond is the limited hold (LH).
   5. Nose poke responses into the illuminated aperture result in the delivery of a sugar pellet to the magazine and illumination of the magazine light; such responses are considered correct responses. Extinguish the magazine light and initiate the next trial upon pellet retrieval.
   6. Nose poke responses into unlit apertures (incorrect responses) and failures to respond during the LH (omissions) result in a time out (TO). Extinguish the houselight during the TO. Signal the beginning of the next trial at the end of the TO by illuminating the houselight.
   7. Score nose poke responses during the ITI as premature responses; punish these responses with a TO period. Reinitiate the same trial after a TO caused by a premature response.
   8. End each session after 90 trials or 30 min, whichever comes first.
   9. For the first stage of training set the stimulus duration to 30 sec, the LH to 30 sec, the ITI to 2 sec and the TO to 2 sec. Adjust these parameters across training such that the stimulus duration is 1 sec and the LH, ITI and TO are all 5 sec (see Table 1). Move rats to the next training stage once they have reached the suggested training criteria. Test rats after they exhibit stable performance on the final stage.
      Note: Sprague-Dawley rats typically reach criterion performance (~65 % accuracy, < 20% omissions) within 4-8 weeks if trained 5 days per week. Different strains of rats however, have different abilities to perform the task. For example, Lister Hooded rats can attain high levels of accuracy (> 80%) with fewer omissions (< 20%) using a short stimulus duration (0.5 sec) (e.g., Bari et al., 2008; Mizra and Bright, 2001). It is recommended that researchers adjust stimulus parameters and criterion performance to reflect strain of rat (or mouse) used.
4. 5CSRTT Testing
   1. Calculate baseline performance (% accuracy, % omissions, premature responses) by averaging performance on each measure across the last 3-5 sessions (see below). Use these data to divide rats into groups (if required) or as an individual rats’ baseline.
   2. Use test day challenges (Table 2) to further probe behavior.
   3. For within subjects designs, intersperse training sessions with test day challenge sessions.
      Note: Test day challenges can be used to complement examination of behavior on the standard task. These manipulations can reveal subtle changes in behavior that are not apparent after extensive training on the standard task and/or be used to gain a better understanding of the nature of a performance deficit.
5. 5CSRTT Performance Measures
   1. Use a computer to calculate performance measures.
   2. Accuracy of responding (% accuracy): Divide the number of correct responses by the total of correct and incorrect responses. This is the primary measure of attention.
      [# correct responses/(# correct responses+ # incorrect response)] x 100
   3. Omissions: Divide the number of trials in which the rat did not respond by the total number of trials completed. % Omissions can reflect attention, but can also be influenced by sedation, motivation and motor ability, thus the interpretation of omissions depends on other performance measures.
      [# omissions/(# omissions + # correct responses + # incorrect responses)] x 100
   4. Correct Responses: Divide the number of correct responses by the total number of trials completed.
      [# correct responses /(# omissions + # correct responses + # incorrect responses)] x 100
   5. Incorrect Responses: Divide the number of incorrect responses by the total number of trials completed.
      [# incorrect responses /(# omissions + # correct responses + # incorrect responses)] x 100
   6. Premature Responses: Determine the number of responses made during the ITI. This is the primary measure of impulsive behavior.
   7. Perseverative Responses: Determine the number of nose poke responses into any aperture after the rat has made a correct response but before retrieval of the sugar pellet. This is a measure of compulsive behavior.
   8. Magazine Entries: Determine the number of nose poke responses into the magazine. This is a measure of motivation.
   9. Latency to Correct Response: Calculate the average time from the onset of the stimulus to a correct response; a measure of processing speed or decision-making.
   10. Latency to Incorrect Response: Calculate the average time from the onset of the stimulus to an incorrect response; a measure of processing speed or decision-making.
   11. Reward Retrieval Latency: Calculate the average time for a rat to retrieve the sugar pellet reward; can reflect motivation.

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Results

Manipulations of the 5CSRTT that Probe Visuospatial Attention

One approach to varying the attentional demands of the task is to alter the duration of the stimulus. As the stimulus duration decreases, % accuracy decreases (Figure 3A) and % omissions increase (Figure 3B; adapted from 12). Thus shorter stimulus durations increase the attentional demands of the task and longer stimulus durations decrease the attentional demands of the task. Chang...

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Discussion

The 5CSRTT is a widely used task to assess attention and impulse control in rodents. Attention is most commonly measured by accuracy of responding^1,7,10. Because accuracy of responding does not include omissions and because both correct and incorrect responses have the same response requirement (i.e., a nose poke in an aperture), accuracy is not influenced by locomotor ability, motivation or sedation. The % omissions can also be used as a measure of attention because well trained rodents will...

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Materials

Name	Company	Catalog Number	Comments
Five Hole Nose Poke Wall Chamber Package	Med-Associates	MED-NP5L-D1	Alternatively one could use the standard package (Catalog #:MED-NP5L-B1) Deluxe
Dustless Precision Pellet	Bio-Serv	F0021	45 mg Purified