BY KELLY NORTH
In a study performed by Dr. Joseph Miele, Gina Colonna and I at East Stroudsburg University, Long-Evans rats were capable of learning to use a tool to retrieve food out of reach.
Psychologists have long been interested in tool use by animals. By 1980, evidence of tool use had been presented across most of the animal kingdom.
Very little work has been reported on tool use in rodents. Rodents, such as badgers, have been found to use tools in nature, and more recently in a study performed by researcher Okanoya and his colleagues, Octodon Degus have been trained to use tools in the laboratory.
However, rats and mice are widely used in behavioral research in the United States. Rockland-Swiss mice were recently shown to be capable of tool-use in the laboratory during a study directed by Dr. Miele.
In the our study, we wished to expand this research to laboratory rats as well. A rake was used to retrieve a piece of food beyond the direct reach of the rats to show if Long-Evans rats could learn to use a tool in a similar manner as other rodents.
Eight male Long Evans rats were used in this study. They were purchased at thirty days of age and housed in groups of two or three in a temperature controlled colony room.
The training apparatus was a standard clear rat cage that was modified for this experiment. The cage was devided in halves by a quarter inch of plexglas raised one centimeter from the floor of the cage. A metal cage top was used to secure the rat inside the cage during sessions.
The tool used for retrieving the food reward was a small wooden Zen garden rake, measuring three centimeters wide, with a ten centimeters handle.
At sixty days of age, the researchers placed black marks on the tails using permanent marker to identify cage-mates. Food was removed from the home cage at several hours the day prior to testing. Food was provided immediately following testing.
Each rat received one session of habituation (Phase One). This consisted of five 2-minute trials, with inter-trial intervals averaging 60-seconds. A trial consisted of placing the treat in the same side of the test chamber as the rat. On each trial, a new treat was given.
Rats were considered habituated if they ate the treat on 3 of 5 non-consecutive trials in a single session. All rats met this criterion after one session.
In the second phase of the study (tool-use opportunity) the rats were exposed to four tool-use sessions. A trial consisted of placing the treat on the opposing side of a divider, approximately 2cm away. The rake was placed so the grabbing end was just behind and touching the treat. The rake handle was positioned perpendicular and slid underneath the Plexiglas and accessible to the rat on the other side of the divider. The position of the rake handle was randomly determined.
During each two minute trial, the researchers recorded the number of seconds to pull rake, whether the rake pull was partial or complete and if the rat ate none, some, or all, of the treat.
In the third phase, the rats were allowed to experience three tool-interactions sessions. During each ten-minute session, the rake was placed on top of the treat on the same side of the test chamber as the rat. Interaction with the tool and treat was observed and recorded.
During each session, researchers recorded number of seconds to interact with the rake, whether the rake was nosed or pawed, and if the rat ate some or all of the treat. The tool-use chamber, partition, and rake were thoroughly cleaned between sessions.
The fourth and final phase of the study was similar to the second phase, consisting of ten additional tool-use opportunity sessions. Measures were recorded as during the first phase.
Six of eight rats were able to use the tool to retrieve food by the end of training. We did not see the rapid developing tool-use found by Okanaya and his colleagues while studying Degus. However, they used a more compressed training schedule, with many trials over a single session over five consecutive days.
Okanoya employed a more enriched environment, with cages that contained tunnels, a running wheel, and sleeping den with nesting material. Long-Evans rats lived in standard polypropylene cages containing, corn cob bedding. Moreover, the researchers seemed able to overcome the relative depravity of our housing environment by providing three sessions of free interaction with the rake tool between phases one and three.
Researchers Bentley-Condit and Smith have provided a compelling and comprehensive catalog of animal tool use and tool manufacture. They define ten tool use categories but argue almost eighty five percent of animals use tools in only one of the tool use categories. Only Passiriformes and Primates use tools in four or more categories.
This research with the Long-Evans Rats did not seek to produce or assess the functional understanding of tool-use, though it should make for an interesting line of future research.
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