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Learning to drive small cars helps rats feel less stressed, scientists found.

Researchers at the University of Richmond in the US taught a group of 17 rats how to drive little plastic cars, in exchange for bits of cereal.

Study lead Dr Kelly Lambert said the rats felt more relaxed during the task, a finding that could help with the development of non-pharmaceutical treatments for mental illness.

The rats were not required to take a driving test at the end of the study.

Dr Lambert and her colleagues built a tiny electric car by attaching a clear plastic jar to an aluminium plate, fitted to a set of wheels.

A copper wire was then threaded horizontally across the jar - the cab of the car - to form three bars, left, right and centre.

To drive the car, a rat would sit on the aluminium plate and touch the copper wire. The circuit was then complete, and the animal could select the direction in which they wanted to travel.

After months of training, the rats learned not only how to make the ratmobile move but also how to change direction, researchers wrote in the journal Behavioural Brain Research.

Some of the rats in the experiment had been raised in a lab, while others lived in "enriched environments" - that is, they had more natural habitats.

The rats raised in "enriched environments" were significantly better drivers than the lab rats.

After the trials, researchers collected the rats' faeces to test for the stress hormone corticosterone, as well as for dehydroepiandrosterone, an anti-stress hormone.

All of the rats had higher levels of dehydroepiandrosterone, which the scientists believe could be linked to the satisfaction of having learned a new skill.

Dr Lambert told AFP news agency that the findings could prove useful for future research into treatments for different psychiatric conditions.

"There's no cure for schizophrenia or depression, and we need to catch up," she said.

"I think we need to look at different animal models and different types of tasks and really respect that behaviour can change our neurochemistry."