The overall goal of this procedure is to train a rat to perform a sequence of tasks by which multiple brain functions can be investigated. This is accomplished by first acclimating the rats to the behavioral chamber. The second step is to train the rat to push a lever to obtain food pellets as rewards.
Next, the rats are trained to reveal a hidden lever by poking their head into the nose poke hole. The final step is to train the rats to recognize a sensory cue and then to push the correct lever indicated by the queue. Ultimately, the rats learn the entire sequence of the tasks aimed at obtaining the rewards.
We have developed a a fully automated system for right behavioral testing and neuronal activity recording. Using this system, multiple brain functions can be investigated. The unique future of this system is a customer made acoustically transparent chamber, which is ideal for auditory task training.
Another feature of this system is that different operant devices can be added easily, which makes the system quite versatile, allowing the implementation of a variety of auditory, visual, and audiovisual behavioral tasks. The system is composed of three major components, a double walled soundproof room, a multiple channel electrophysiological recording system, and a fully automated behavioral testing system. A custom designed opera in chamber sits inside the soundproof room.
The chamber consists of three acoustically transparent walls and one modular operation panel to monitor and record behavior. A video camera is mounted above the opera in chamber. An interface box transmits signals back and forth between the chamber and a computer.
Auditory cues are generated by a calibrated programmable audio generator and are delivered via three speakers located on the operation panel for visual cues, a stimulus light and two triple stimulus displays are located on the middle and side panels. A nose poke device with three color LED lights is mounted at the bottom of the middle panel. An infrared detector installed within the nose poke unit records, nose poking and holding.
Period two removable retractable response levers are mounted on each side of the operation. Panel rewards are provided by two pellet dispensers that drop food into the pellet receptacles. Four pairs of infrared beams are placed at the bottom of the chamber to both indicate the position of the animal and to control devices based on the animal's position.
Lastly, cables from a head stage are connected to a commutator for recording neuronal activity. The experimental protocol is fully automated via programs created within the Med PC four software platform. Behavioral data are saved and translated to Microsoft Excel files then imported into and analyzed with matlab.
Before training, limit the food intake until the animal's weight is 90%of baseline. To prepare the chamber for acclimation, retract the levers, block the nose poke hole with a rubber stopper, and place about 20 pellets of food into each pellet. Receptacle now place a naive animal into the chamber for acclimation.
The rat will soon start to explore the food cups and eat the pellets. When both food cups are empty, use the software to dispense a single pellet into each tray. In doing so, the rat will learn to associate food with the cup.
Force the rat to move to both sides of the chamber by dispensing pellets randomly into each food cup. One session is usually enough for establishing the Food Cup Association In a new session, extend both levers into the chamber and leave the food cup empty. Next place an acclimated rat into the chamber.
When the animal enters the vicinity of a lever, dispense a pellet. Also provide rewards when the rat shows interest in the lever, such as sniffing, touching, or climbing. An accidental lever push should also trigger a reward.
To encourage lever pushing and to force exploration of both levers, allow the animal to push each lever consecutively a limited number of times when the limit is reached, retract the lever. Extend both levers to repeat the procedure. Gradually decrease the limit until the lever retracts every time it is pushed.
One to two sessions are usually enough for establishing the lever. Push Food reward Association. In a new session, retract the levers.
Remove the rubber stopper from the nose poke hole, and place several food pellets in the nose. Poke device. Reintroduce the animal into the chamber and extend one of the two levers randomly.
When the rat sniffs the nose poke hole for food pellets, seeing the extended lever, the rat will approach and push the lever to obtain a food pellet. After the is pressed and the reward is dispensed, retract the lever to encourage the rat to explore the nose poke device. It usually takes one 30 minute session for a rat to learn the task sequence, nose, poke, lever, push rewards.
In another new session, place the animal into the chamber to begin Q training. After the animal performs a nose poke event, play a distinct auditory cue. Extend both right and left levers.
After each auditory cue presentation, reward the rat only when it pushes the lever that is indicated by the auditory cue, the animal will gradually learn to associate a specific auditory cue. With one lever. The animal should now be able to perform the intended full sequence of training, nose, poke, cue, lever, push, reward, or no reward.
Allow the rat to practice the newly learned task until a consistent performance level is reached. The session is limited to 30 minutes. This system can be used to perform the two alternative choice pitch discrimination task, which examines the frequency discrimination threshold of a rat.
After training the rats to quickly push the correct lever indicated by an auditory cue, an auditory learning curve is obtained. Each colored line represents the discrimination frequency variations of an individual animal. The dark line represents the averaged learning curve.
On average, it took about seven sessions of training to attain the 75%hit rate.Criterion. Animal behavior in this task can also be quantitatively characterized by several measurements, including the reaction time relative to the onset of the auditory queue, the inter trial interval, and the temporal dynamics of performance. Multiple cognitive brain functions can also be investigated using this system.
The top captions describe each action in sequence of one trial. The bottom captions indicate the cognitive behavioral functions that can be studied when combined with electrophysiology. Recording the neural basis of the cognitive behavioral functions can also be studied.
This plot shows a neuron recorded in the nucleus space ssus of a rat performing the two alternative choice pitch discrimination task. While this plot shows a neuron recorded in the ventral segmental area, When attempting this procedure is important to pay close attention to, to differences between rats and their behavioral characteristics, and cognitive ability, training procedures and parameters should be individualized for best training results. Although we developed this system mainly for study auditor system, it can be easily adapted by other research to study a visual system and multiple cognitive brain functions such as motivation, attention, patients, and rewards.
