Rodents rake for rewards

In the past, the use of tools enabled humans to adapt to different ecological niches. The resulting new experiences presented more learning opportunities, extending our brain capacity.

Now researchers at the RIKEN Brain Science Institute in Wako have trained degus, a medium-sized rodent native to Chile, to use tools. The study shows that degus could be a useful animal model for directly observing how tool use modifies brain behavior¹.

“Rodents are cheaper and smaller than primates,” explains project-scientist Kazuo Okanoya. “Also, techniques for genetic manipulations are more advanced for rodents and we could modify these existing procedures for degus.”

The researchers originally chose to study degus because they noticed that the animals are playful, highly inquisitive, and have good manual skills (Fig. 1). Adult degus were placed in a chamber with openings that the degus could put their hands through. Food was placed just beyond the animals’ reach, while a rake-like tool was placed within their reach.

To begin with, the food was placed behind the rake’s blade, so that all the degus had to do was pull the rake handle. Once they had mastered this, the task was made more difficult by placing the food in front or to one side of the tool. The degus soon began to try out new movements such as pushing the tool or wiggling sideways. With more practice the movements merged into one smooth trajectory and the degus were seen to stare at the food rather than at the tool, suggesting that the tool was becoming an intuitive extension of their own arms.

Furthermore, the degus adapted to tools of different sizes, shapes and colors, and quickly learned to ignore tools that didn’t work. This shows that the animals gained a mental appreciation of the tool’s function.

The results for degus compare favorably with previous studies on primates. The researchers expect that tool use produces new connections between different areas of the brain, leading to improved hand–eye co-ordination. “We are confident that other rodents could also be trained to use tools, although it might take longer than for degus,” says Okanoya.

In the future, Okanoya would like to study the links between tool use and voice. “We think the site where these two activities overlap could be a precursor for the brain areas related to language production,” he says. “Thus, the current tool use study can lead to the study of the origin of language.”