The overall goal of the following experiment is to assess behavioral flexibility, including set shifting and reversal learning in rats using an automated operant based method. This is achieved by first pre-training the animals on the lever pressing behavior to familiarize them with the extension and the retraction of the levers and ensure consistent reporting. Next, the animals are tested on the first task of the desired sequence.
For example, the visual cue discrimination in the queue to response sequence, which establishes the animal's ability to learn a discrimination rule. Then the animals are tested on the second task of the desired sequence in order to assess animal's behavioral flexibility, which is their ability to shift from one rule to another. The results show effects on different aspects of behavioral flexibility based on various pharmacological or anatomical manipulations.
The main advantage of this technique over existing methods like maze based or digging tasks, is that there is greater stimulus control and standardization, and the rate of data collection is greatly increased. Demonstrating the procedure will be Bradley Roberts, an undergraduate student from my laboratory For carrying out behavioral flexibility tests in rats. Use operant chambers equipped with a minimum of two retractable levers placed on either side of a central reinforcement delivery area, two stimulus lights, one located above each lever, a house light and a reinforcement dispenser.
Ensure that the house light illuminates the entire chamber while not interfering with detection of the stimulus lights. Use palatable food for reinforcement such as 45 milligrams sucrose pellets. Control the stimulus presentation, lever operation and data collection via an interface with a computer.
Refer to the text protocol for additional details to pre-train the rats. Following the guidelines in the text protocol, give the rats retractable lever training sessions to familiarize them with the extension and retraction of the levers and to ensure that the rats are making relatively few omissions by the time they proceed to the main test phases of the task. During each trial, determine which lever to extend alternate lever extensions in a pseudorandom order such that there are 45 left lever trials and 45 right lever trials, but no more than two consecutive trials.
Extend the same lever, extend the selected lever. Reinforce the animal after it presses on the lever within 10 seconds after which time the lever is retracted. If the animal does not respond within 10 seconds, retract the lever and record an omission.
Continue 30 minute retractable lever training sessions for a fixed number of days or until animals meet a minimum criterion of five or fewer omissions for two consecutive days to test animals on the queue to response sequence, which represents one of the two possible testing sequences for strategy shifting. Begin testing animals on the Q task. This task reinforces animals to respond to the lever below the illuminated stimulus light, and is the set task in the sequence.
Begin each trial with both levers retracted, illuminate either the left or right stimulus light for three seconds. Then extend both levers into the chamber for 10 seconds or until a response occurs. Reinforce only a correct response on the signaled lever upon a response on either lever.
Retract the levers. Begin trials every 20 seconds throughout the session. Pseudo randomly determine the order of trials such that no more than two consecutive trials occur with the same stimulus.
Light illuminated. Continue trials until an animal has completed 10 consecutive correct responses and has completed a minimum of 30 trials or until 150 to 200 trials are completed without reaching criterion. On the next day, after reaching criterion on the Q task, shift animals to the response task, which represents the shift task in the sequence, and which reinforces animals for responding on the lever opposite their side preference.
Regardless of the cue beginning with both levers retracted pseudo randomly illuminate either stimulus light for three seconds, then extend both levers into the chamber for 10 seconds or until a response occurs. Reinforce only a response on the correct position lever opposite of the animal's side, preference upon a response on either lever. Retract the levers, continue trials until the animal has reached the criterion of 10 consecutive correct responses.
Efficient strategy shifting is dependent on the medial prefrontal cortex. On the first day of treatment, prefrontal inactivation did not impair performance on the Q set task. However, prefrontal inactivation on the second day significantly impaired performance in the response shift task in that animals required more trials to reach criterion performance.
In comparison, reversal of response, discrimination did not show dependency on the medial prefrontal cortex. Animals receiving inactivation of the prefrontal cortex on the reversal day did not differ from saline infused animals, which supports previous research showing that the orbital frontal cortex, not the medial prefrontal cortex, regulates reversal learning on a variety of tasks. To demonstrate how reminder trials can aid in data interpretation, rats acquired a Visual Q rule on day one.
On day two, rats received vehicle or hallal peritol and then were given 20 reminder trials from day one before switching to response discrimination. The results show that hallal peritol impaired retrieval of the visual cue during the reminder trials. Subsequently, the hallal peritol treated rats required fewer trials to achieve criterion, an outcome that may have been interpreted as an improvement in set shifting if reminder trials had not been available to indicate that memory was actually impaired for the previous rule.
Other methods like anatomical, environmental, or genetic manipulations, as well as physiological or chemical recording techniques can be added to this procedure in order to explore the neurobiological basis of behavioral flexibility and executive function.
