Archive for November 6, 2008

WHY did they stop hoarding?

Over the past few days, we have noticed that the rats have plateaued at an all time low number of hoarded pellets. Over the last 4 trials, Penelope has hoarded an average of 8.33 pellets and eaten an average of 7.67 times. Louise has hoarded an average of 8.67 pellets and eaten an average of 5.33 times. This wouldn’t be such a worry for us and we would continue with the current experiment plans; however, we know that 1) hoarding a large number of pellets is a known natural behavior for rats, and 2) we have observed the rats hoarding many more pellets under other circumstances (i.e. when Penelope hoarded 30+ pellets on the first day and when they hoard a large amount of pellets while in their home cages.) Thus, although we began our experimental process by investigating whether rats hoard more when alone or when together, we have molded our experiment to simply find out WHY both rats stopped hoarding.

Like we have said before, there are many things that affect hoarding behavior, and therefore many variables that we could manipulate. We will attempt to tackle a number of these variables to see what will and will not increase the number of pellets hoarded, from our low baseline. We know that our baseline includes a foreign environment, delivering the pellets in piles of five into a plastic container, and a relatively small space. We will keep these variables in mind when we change other aspects of the experiment, and we will attempt to control for as many things as possible.

We will be focusing on the following specific changes:

1) Although research suggests that hoarding is based on deprivation, we will try to make the rats as full as possible and see if they hoard more (or at least eat less!)

2) Changing how food is delivered to the rats — Instead of delivering it in piles, we will deliver each pellet one-by-one by hand.

3) Although pellet size has also been shown not to make a significant difference in number of pellets hoarded, we will use bigger pellets so that perhaps they are less likely to eat the pellets.

4) We have already attempted to take pellets away once they are hoarded to prevent the rats from eating and to see if this would motivate them to hoard more (or faster.) As a result, Louise began to “protect” her food by standing over it and watching for our hands. It also just made her eat the pellets faster!

5) We have read literature that suggests that rats will hoard more in a familiar environment that in a novel one (however, we also read that rats habituate to novel environments and hoarding will eventually even out.) We have also observed each rat hoarding food within their own cages, and when we continuously delivered individual pellets to the rats in this environment, they hoarded a large number of pellets! Thus, we would like to see how they would behave in a more controlled, yet familiar, environment. In order to keep things as controlled as possible, we will place a cloth in each rat’s cage, hoping that the cloths take on each rat’s scent. The hope is that when we place this in the experimental environment, the rats will feel comfortable, and hoarding will increase. We may also add a small “cubby” (probably made of a shoe box cut in half) inside which we will place the “familiar” cloth. This may also stand as a home environment, and may increase hoarding. Here is a picture of one of the rat’s cages with the cloth inside:

penelope-200

6) It is possible that our experimental environment is too small — it may be unnatural to find food so close to where they must hoard (maybe the environment is too ambiguous.) Thus, we could remove the wire mesh barrier and allow the rats free reign of the entire tank, delivering the food at one end of the tank. We were also brainstorming new apparatus ideas and came up with the following:

ratapparatus1

Using the same glass tank, we could section off two corners and part of the long side of the tank, creating a chute down the middle and an open section at one end. We would place the food at the end of the chute and hope that the rats would bring the food back to the open end. We could even add the cloth and cubby to this environment.

We were also thinking it could be as simple as just removing the wire mesh barrier, adding the “cubby,” and placing the food at the far end of the tank like this:

ratapparatus2

Finally, here is a video of the hoarding behavior we have observed in the home cage environment. We hope this will translate to the experimental condition given our new plans!

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November 6, 2008 at 4:17 am Leave a comment


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