The overall goal of this behavioral task with touchscreen operant chambers is to measure the sustained attention capacity of rats. This method can help uncover the neuro biological mechanisms critical for appropriate sustained attention which is the monitoring of intermittent and unpredictable events over time. The main advantage of this technique is that we have adapted a well validated rodent sustained attention task to the touchscreen operant chamber.
An apparatus of growing popularity with programmability to many cognitive tasks. The applications of this technique extend toward the study of neuropsychiatric and neurodegenerative disorders characterized by disrupted attention. Therapies for which, can be tested using the method presented here.
Generally, individuals new to this method will struggle with setting up a system to ensure that the rats are being accurately tracked and that the data is being properly recorded. For this experiment, touchscreen chambers must be prepared within sound attenuation cubicles. Equip the chambers with the house light, a tone generator, a camera positioned above, a touchscreen and a pellet dispenser with the feeder reward area.
The feeder reward area can be illuminated. Before loading the 45 milligram reward pellets, shake the dust off them using a flour sifter. This dust can clog the feeder.
If the rats are outfitted with a head implant, use a feeder with a large aperture. Feed each chamber with a black acrylic mask to limit the response areas on the touchscreen. Leave a central circular hole for the light stimulus and two square response holes below the central hole positioned center.
While in use, operate the chamber in a sound attenuation cubicle. This completes the chamber preparations. The text protocol describes how to set the perimeters for the experiment.
For this experiment, rats can be housed individually or in groups. Prior to starting a study, handle the rats daily for five minutes per day, for five straight days. Always wear personal protective gear.
Start the food restriction three days before starting the behavior shaping. On the first day, record each rats free-feeding weight and calculate their target weight which is 85%of the free-feeding weight. Prior to shaping, pre-expose the rats to 15 food reward pellets in their home cage.
After the initial food restriction, adjust the food intake to maintain the target weight, allowing for slight weight gain over time. Prior to starting a new schedule, food restrict the rats a little more than usual, to increase their motivation. On days that rats do not perform the task, increase their food by at least one gram to compensate for not receiving pellet rewards.
After each session, wait at least 30 minutes before providing food, to avoid making an association between the testing succession and their feeding time. If the rats are group housed, feed them separately for an hour before regrouping them. In preparation, power up the equipment.
Ensure that the pellet dispensers are filled with pellets and ensure that the mask is in position in front of the touchscreen. Then, check the function of each box. Test the pellet dispenser, the screen, the lights and the tone generator.
Testing the function of the chambers at the beginning of each day is critical because any one small malfunction can confuse the animals and prevent them from learning the task or performing at a normal level. Next, review the schedule for loading the boxes. Pay close attention to the test group and input the relevant information regarding animal ID, sex, experimental condition, user initials and other notes.
With all the preparations made, retrieve the subjects. Generally, test the rats at least 30 minutes into their dark cycle. To work with the rats in the dark, use head mounted red lights.
When transporting the rats during the dark cycle, cover their cages with black towels. Once in the behavior room, load the rats into their appropriate box and start the session for the sustained attention task. In the sustained attention task, rats are trained to distinguish signal trials from non-signal trials.
Signal trials include a variable duration light flash followed by an audible tone and a four second response window. During the four seconds, if the rat then posed the correct area on the screen. In this case, it is the right response area, the rat is rewarded with a food pellet and this is called, a hit.
If the rat pokes the other response area, this is considered a miss and the rat is not rewarded. A non-signal trial does not include the light and the rat must poke a different part of the screen to indicate that no signal was detected to earn a reward. A correct response on a non-signal trial is called, a correct rejection.
If the rat pokes the other response area on a non-signal trial, this is considered a false alarm and is not rewarded. The correct response areas for signal and non-signal trials should be counter-balanced between subjects. For signal and non-signal trials, a failure to make any response during the response window counts as a, no mission and is not rewarded.
There is also a distracter version of the sustained attention task, where the house light flashes during the second of three blocks of trials. After starting a session, monitor the rats during the first several minutes, to ensure that everything is functioning properly. Then, check their performance intermittently.
Once a session is complete, record the summary data and any issues in the notebook. Between trials, wipe down each chamber with 10%ethanol and replace the bedding. After running all the trials for the day, thoroughly clean the chambers with 10%ethanol, making sure the floor grid is as clean as possible.
Then, replace the bedding. After every session, it is a good idea to fully update the spreadsheets and back them up to a separate server. The median number of days to reach criteria on SAT was 54.5 days for male rats and 62 days for female rats with no significant difference.
Performance measures on the SAT task showed that based on the percentages of hits and correct rejections, males and females were similarly accurate on the signaled and non-signaled trials. An overall measure of intentional performance, the vigilance index or VI, showed similar measures between the sexes as well. Nor were there sex differences in the low percentages of omissions recorded.
During the tasks, the visual signal varied between 500, 50 and 25 milliseconds and performance declined with the shorter signals. There was no main effect based on sex. To increase attentional demands, the house light was flashed as a distracter during the second of the three trial blocks, in one subset of rats.
As expected, there was a main effect for the trial block. With performance declining in block two and recovering in block three. Unexpectedly, females performed significantly worse than males.
After watching this video, you should have a good understanding of how to test sustained attention in rats using touchscreen operant chambers. While attempting this procedure, it's important to remember to keep track of each individual animal's performance and adjust feeding as necessary to ensure that they have acquired the task as quickly as possible. Don't forget, that when working with rodents, protocol should first be approved by IACUC and personal protective equipment should always be worn.
