Mice and rats have long been used in medical research because of their biological similarities to humans.The tiny animals have already shown an ability to recognize objects,push buttons and find their way through complex paths.Now, scientists have trained rats to drive small vehicles created for them.One of the main findings of the experiment was that the driving activity seemed to help the rats relax.Researchers at the University of Richmond in Virginia led the experiment.Their findings were published in Behavioural Brain Research.The team built tiny cars out of plastic and other materials.The vehicles had an opening at one end where electrical wires were attached.By touching one of three different wires,the rat could steer the car in different directions – left, center and right.Sweet treats were placed inside the experiment containersin an attempt to get the rats to drive the vehicle to get to the food.Researchers trained 17 rats over several months to drive around the containers.The animals proved that they could be trained to drive forwardas well as in other directions to get to the treats.Kelly Lambert of the University of Richmond helped lead the experiment.She told the French news agency AFP the research suggeststhat rat brains may be more complex and flexible than once thought.Lambert said she had long been interested in neuroplasticity,or the way the brain changes to react to different experiences and difficulties.She found that rats kept in what she calls "enriched environments"performed far better than those in labs.While she expected that result, Lambert told AFP"it was actually quite shocking to me that they were so much better."The researchers examined levels of two hormones in the rats– one that causes stress and another that counters it.All rats that took part in the training had higher levels of the hormone that reduces stress.The research suggests the increased relaxation levelscould be linked to the enjoyment of successfully completing a new skill.The team also found that the rats that drove themselvesshowed higher levels of the stress-fighting hormonethan those that simply rode in small cars controlled by humans.Lambert said the most exciting result of the experiment for herwas about the possible effect on humans.The research may open new areas of non-drug treatments for peoplesuffering from mental health conditions."There's no cure for schizophrenia or depression and we need to catch up," she said."And I think we need to look at different animal models and different types of tasksand really respect that behavior can change our neurochemistry."Speaking to the British-based magazine New Scientist,Lambert said her team is planning to continue experimentsto learn more about how the rats learned to drive.The new research will also examine why some activities appear to reduce stress,and which areas of the brain are involved in the process.As an example, Lambert said new driving tests could be createdto test the effects of Parkinson's disease on motor skills and awareness of space."If we use more realistic and challenging models,it may provide more meaningful data," she told New Scientist.