The overall goal of this protocol is to measure aspects of attention in rats and mice, similar to those measured by the human Psychomotor Vigilance Test, such as accuracy, motor speed, and vigilance. This method can help answer key questions regarding neurobehavioral performances in rodents, including the effects of lesions, pharmacological manipulations, genetic modifications, and sleep deprivation or restriction. The main advantage of this technique is that it provides a stable baseline for assessing the effects of a wide variety of experimental manipulations.
To pretrain the rodents, first assign each animal to an operant chamber, where it will be tested each day at approximately the same time, prior to daily feeding. It is critical that the behavioral data be examined each day before moving them to the next training step. If it is not done at the right time, the result will be poor performance.
Prepare the operant chamber by loading the pellet dispenser with food pellets. Then deliver 10 to 20 food pellets to the food receptacle in the chamber. Then, weigh the animal, in this case a rat, and place it in the operant chamber.
For pre-training, the experimental parameters should be low, fixed values. Once started, the computer program controls the presentation of the house lights, the nose poke key illumination, and automatic dispensing of food pellets. Use settings that will give the animal ample time to explore and be rewarded, such as 10 seconds of nose poke key illumination.
Once the rat finishes the food pellets, start to manually shape the rat's behavior. Leave the cubicle open and watch the rat's behavior. Using a handheld switch wired to the feeder, provide pellets as quickly as possible after the rat performs the desired behavior.
Shape successive approximations of the desired behavior. For example, once the rat reliably retrieves food pellets from the food receptacle, shape it to move to the left after retrieving a food pellet, towards the nose poke key. During the shaping process, keep the computer program running and controlling the house light, nose poke key, and feeder.
Thus, if the rat pokes the key, the computer program reinforces the behavior automatically. After the session, count the total number of pellets the rat receives, and subtract this total mass of food from the rat's daily food allotment. 30 minutes or more after the session, feed the rat the remainder of its daily rations.
Clean the operant chamber daily with a gentle disinfectant. Use 70%ethanol sparingly. Check the nose poke key functionality daily, and clean it as needed.
Pretrain each rat until it scores at least 40 computer reinforced responses on the illuminated key and retrieves each food pellet. Usually two or three half hour sessions will be enough. Once the rat's behavior is shaped, train the rat with an initial two second, foreperiod interval, and two second timeout.
Illuminate the nose poke key as long as needed to get a response, such as nine seconds. This is the limited hold value of the program. Use the timeout as a punishment for premature responses, or when the rat responds prior to the illumination of the nose poke key.
During the timeout, the rat has no opportunity to earn food. Proceed by running the 30 minute session. Once the rat completes eight out of 10 correct trials at the current foreperiod value, have the computer increase the foreperiod value and timeout by a tenth of a second.
And also, shorten the limited hold value by a tenth of a second. These tenth of a second increases to the foreperiod and timeout values, and decreases to the limited hold values, occur repeatedly within each session as the rat completes eight out of 10 correct trials at each foreperiod value. Once the 30 minute session is over, record the maximum foreperiod length achieved by the rat in a session, and how many pellets were earned.
As during pretraining, subtract the amount of food consumed from the rat's daily allotment. The next day, start the 30 minute training session with a foreperiod that is 300 milliseconds slower than the maximum value achieved in the previous session. As the rat achieves eight out of 10 correct trials at each foreperiod value, the computer program will continue to automatically increase this value just as the day before.
When the timeout reaches eight seconds, and the limited hold reaches 1.5 seconds, advance these variables no further. The foreperiod can get as long as tolerated. Analyze the rat's daily performance as the percentage of correct trials, premature trials, and misses.
Rats commonly maintain an average of 40 to 90%correct responses with steady improvement. Once the rat reaches a foreperiod of 10 seconds or more, vary every foreperiods in the trial from seven and 10 seconds, while keeping the other parameters fixed at eight and 1.5 seconds. When a rat is able to get 70%of the trials correct, with a variable foreperiod, extend the range of the variable foreperiod to five to 10 seconds.
This often occurs within a session, so it is good to keep a close eye on the data. Again, after the rat is able to complete 70%of the trials successfully, broaden the variable foreperiod range to three to 10 seconds. It is really important that the rat get 70%or better success before advancing the degree of difficulty.
Because some rats will adopt a strategy of responding randomly, instead of waiting for the stimulus. With the parameters detailed here, 86.7%of 122 male rats reached the final rPVT parameters within an average of of nine computer automated training sessions. The reaction time of rats was then compared to that of humans performing the PVT.
Like humans, rats show the expected sharp rise in reaction times at the lower values, with a longer rightward tail at the higher values. As seen in the human PVT, the rats'response speed decreases over time on task, which indicates a vigilance decrement, or a decrease in performance, as the amount of time performing the task increases. Foreperiod time had a significant impact on the rats'performance.
At lower foreperiod values, performance was slower and contained a greater percentage of lapses. However, as the foreperiod time increased, correct responding decreased while reaction times were faster, and the percentage of premature responses increased. After watching this video, you should have a good understanding of how to train rats and mice to accurately perform a rodent version of the human PVT, and obtain stable, consistent performances on a daily basis for months.
Once mastered, this technique can be used to train rodents to perform the rodent PVT within 10 to 15 days, and produce stable performances thereafter.
