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Researchers in the US have taught a group of rats how to drive small plastic cars, in exchange for reward bits of cereal. After a few months the rats learned how to change the car’s direction. After the trials, all of the rats had higher levels of an anti-stress hormone. Scientists think this could be linked to the satisfaction of having learned a new skill. Dr Kelly Lambert is the lead scientist. She spoke to Â鶹Éç OS. (Photo: A lab rat driving the "RatCar". Credit: HO/University of Richmond/AFP)