The overall goal of this procedure is to detect deficits in a two choice sent discrimination task in rats. This is accomplished by first habituating the rats to the training and testing materials. The second step is to train the rats to uncover and consume reinforcers buried in unscented play sand.
Next, the rats are trained to discriminate between two different scents that have been mixed into the sand. The final step is to test the rats on a series of two choice scent discriminations. Ultimately, the Dig Scent Discrimination Task can be used to show performance deficits in each of the scent pairings in injured rats.
The main advantage of the dig task over other behavioral assessment measures for brain injury is that it is a simple economical task that can be easily incorporated into any existing battery. The implications of this task extend toward therapy for traumatic brain injury cause it evaluates cognitive dysfunction, which is one of the most pervasive deficits following brain injury. Begin by setting up the test apparatus.
The chamber should be large enough to accommodate one animal and two scent cups as seen here. The scent cups should be sufficiently wide and deep to allow for digging and have a holder to stabilize them. Choose scents that were previously established not to show a response bias and mix them at a ratio of one gram odorant to 110 grams of clean unscented playground sand.Here.
Fruit loop cereal pieces are used as a reinforcer. It is recommended to expose animals to the reinforcer in their home cages three to five days prior to training. Food restriction is needed to help motivate animals to perform the task and should be initiated at least three days prior to both training and testing.
And animal weights should be checked every other day for the first session completely fill the scent cups with the reinforcer, place the rat in the chamber and allow it to explore and habituate to the chamber. For 30 minutes, the animal should be allowed to freely consume the reinforcer. The next step is to completely fill the Scent Cups with the reinforcer and pour a small amount of unscented sand into each cup filling no more than half of the cup so the reinforcer is only partially covered.
Place the animal into the apparatus for another 30 minutes and allow it to habituate to the sand to promote surface digging. Fill the scent cups with an even mixture of reinforcer and unscented sand, leaving multiple reinforcers exposed. Place the animal into the apparatus for 30 minutes.
In the process of consuming the exposed reinforcers, the animals should uncover additional reinforcers below the surface of the sand. Encourage further digging by filling the Scent Cups with a mixture of one part reinforcer to three parts unscented sand, leaving one to two reinforcers exposed. Place the animal into the chamber for 30 minutes.
The animal should begin to dig with its four paws to uncover additional reinforcers and remove them from the sand. Next, promote full digging by filling the Scent Cups with a mixture of one part reinforcer to three parts unscented sand, leaving no reinforcers exposed. Place the animal into the apparatus for 30 minutes.
If the animal does not uncover and consume a reinforcer within five to 10 minutes, assist by uncovering a single reinforcer and allowing the animal time to consume it. Some animals may need multiple instances of this session in order to demonstrate full digging behavior. Once digging behavior has been established, place three reinforcers in deep, middle, and shallow positions in the sand.
In each scent cup, place the animal into the chamber until all three are retrieved from each cup assisting as needed. Once all reinforcers have been retrieved, place the animal into a holding apparatus for 15 to 30 seconds and reset the scent cups. Next, place the animal back into the chamber and repeat the process until the animal has completed four total trials.
Ideally, the animal should start digging immediately when placed into the chamber. Demonstrate full digging behavior and retrieve the reinforcer placed at the bottom of the scent cup. Next place a single reinforcer at half of the depth of the sand in each cup.
Place the animal into the chamber and allow it to retrieve both reinforcers and then place it into the holding apparatus For 30 seconds, reset the scent cups and repeat this process. For four total trials, the animal should begin to dig faster and require minimal assistance from the researcher. The next step is mock discrimination testing.
Fill the cup as described in the last session and give the animal 30 seconds to retrieve both reinforcers. Remove the animal from the chamber when both have been retrieved or after 30 seconds. Repeat this for the number of trials that will be used in the testing phase.
Animals should learn to dig rapidly when placed back into the chamber. The animal is unable to retrieve both reinforcers within 30 seconds. Give it some more time or trials.
Eventually the animal will speed up. However, if the animal continues to perform very slowly, place it into the whole clean apparatus for about a five to 10 minute break. After the break, place the animal back into the box and try again.
If the animal is still performing slowly or not responding at all, it may be satiated or full for the day and testing may have to continue. The next To begin discrimination testing, choose ascent to be paired with the reinforcer and another which will not be Prepare the sand as demonstrated earlier. Next, set up the chamber as seen previously, place the reinforcer in one of the cups containing scented sand.
The data for each trial can be recorded by hand and should include correct or incorrect choice Latency. To initiate digging and trials in which a rat times out on to begin a trial, place the animal into the chamber facing the rear equidistant from each cup. Placing an animal closer to one cup may increase the chance of developing a bias.
If the animal correctly discriminates, allow it to retrieve and consume the reinforcer, and then remove it to the holding apparatus for 30 seconds. If it times out or chooses incorrectly, remove it immediately before it corrects itself and place it into the holding apparatus. Repeat this process for the chosen number of trials, resetting the reinforcer and randomizing its position between each trial until the animal achieves a predetermined criterion.
The typical performance of sham control and frontally injured rats across several different phases of testing is shown here. In this example, the data are represented as a bar graph with white dots representing data points for individual rats in each group. The dotted line represents performance at chance level.
Here, the same data is represented in a line graph. There was no difference on the pre-injury discrimination acquisition. However, following injury, sham rats perform the task with more accuracy when compared to injured rats.
When a reversal of the discrimination was administered, injured rats dropped to below chance performance. Similarly, on a novel scent discrimination, frontally injured rats had difficulty learning the novel pairing and stayed at below chance performance. This graph shows typical performance of sham versus unilateral parietal injured rats across several different phases.
The data here are represented as a bar graph with white dots representing data points for individual rats. In each group here, the same data is represented in a line graph. There is no difference between the groups on any of the discriminations unilaterally injured rats performed at, or in some cases slightly higher than sham levels following injury.
The training portion of this task can be completed in as little as four hours. While the testing can take as much time as the researcher deems appropriate, After watching this video, you should have a good understanding of how to administer a simplified set discrimination task for the assessment of deficits after brain injury.
