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In new research aimed at identifying brain changes that underlie the development of tool-use ability, scientists have taught captive rodents to use tools. This is the first report of such training in rodents.

Atsushi Iriki and colleagues at the Brain Science Institute (RIKEN, Saitama, Japan) trained a group of five degus (Octodon degus), small rodents native to Chile, to reach through a fence, grasp a rake and use it to retrieve a food reward that would be otherwise out of reach. They used a step-by-step training procedure with increasing complexity. At the first level, the reward was placed immediately in front of the rake, so that the animal only had to pull the rake toward itself. The distance between the rake and the reward was increased in the second level of training. In the third level of training, the reward was placed to the side of the rake, requiring the animal to move the rake laterally before pulling it in order to retrieve the reward. In the final level, the reward was placed just beyond the rake, such that the animal had to first pull the rake toward itself and then move the rake laterally and away from itself, past the reward, before pulling the reward within reach. The degus mastered each training level and learned to manipulate the rake smoothly (PLoS ONE 3, e1860; 2008), as shown in video clips available online from the journal's website (http://www.plosone.org/).

Iriki's group had previously used a similar procedure to train Japanese macaques, which do not tend to use tools in the wild. As the macaques learned to use the rake to retrieve food rewards, the researchers observed concomitant changes in gene expression and in circuitry in the intraparietal cortex, an area of the brain involved in cognition and processing of sensory input. Iriki believes it is reasonable to assume that similar changes may take place in the rodent brain as a result of tool-use training, and his group has begun studies to address this question. The group is also investigating potential brain changes in marmosets.

Iriki's work may offer insight into the development of tool use in early humans. Tool use is commonly considered to be a mark of advanced intelligence. But the new findings suggest instead that the brain structures involved in tool use may be present, albeit dormant, in many animals.