NEW YORK (Reuters Health) - The difference between being light on one's feet or having two left ones might rest in a part of the brain called the cerebellum, new research suggests.

In brain-imaging experiments, scientists found that while the cerebellum was not particularly active when participants were learning new moves, it got very involved when it came to improving performance.

The findings suggest that the cerebellum may not contribute to learning motor skills, but is primarily concerned with how we perform movement after learning, according to the study authors.

Dr. James Ashe, of the University of Minnesota in Minneapolis, and his colleagues report their findings in the June 14th issue of Science.

According to Ashe's team, the role of the cerebellum in movement is controversial. Some research has shown the brain region to be active during the learning of movement, but because learning also causes changes in performance, it has been hard to weed out just when the cerebellum becomes vitally important.

"Clearly," Ashe told Reuters Health, "the cerebellum is involved in motor skills somehow." This study, he said, suggests "it's in performance."

In their experiments, Ashe and his colleagues had study participants learn a reaction-time task in which they had to move their fingers based on visual cues. The researchers used a technology called functional magnetic resonance imaging (fMRI) to measure participants' brain activity throughout the experiment.

To separate "learning" from "performance," the participants were presented with distractions while they were learning. This kept them from performing well, although actual learning was still taking place. During this test phase, the cerebellum was quiet.

But when participants were tested without distractions, their reaction times and error rates on the task improved significantly, and activity in the cerebellum went up--suggesting, according to the authors, that the cerebellum is important in the performance of learned movement, and not learning itself.

"These results challenge the commonly held assumption that the cerebellum is essential for motor skill acquisition," according to Eliot Hazeltine at the NASA Ames Research Center in Moffet Field, California, and Richard B. Ivry, of the University of California, Berkeley.

In an accompanying editorial, Hazeltine and Ivry note that the findings suggest a new explanation for why people with damage to the cerebellum fail to learn the task used in this study. Instead of this being a problem in patients' learning, the editorialists write, it could be a problem in executing what they've learned.

Ashe agreed that the findings could aid in the understanding of movement problems caused by damage to the cerebellum, such as that seen in some stroke patients.

And although this study doesn't really address it, he said, the findings "could make one wonder" if the cerebellum might "make all the difference" in whether someone becomes Tiger Woods or your average guy on the green.

SOURCE: Science 2002;296:2043-2046.

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