After a few stumbles and bruised knees, bike riding and other so-called motor skills quickly become second nature, and they last a lifetime. Now, a team of neuroscientists reports how this muscular mastery comes about: Within a few hours of practicing a new motor skill, the brain shifts the new instructions from short-term memory to the areas responsible for motor skills. The research, reported in today's Science*, suggests that even though you can't explain how to ride a bike, the brain may learn how to do it just like other more "cerebral" tasks.
A team of neuroscientists led by Reza Shadmehr of Johns Hopkins University had already shown that motor skills become more permanent--and less subject to confusion--several hours after a practice session. Their experiments require subjects to reach toward a series of targets while holding onto a robotic arm, which the scientists can program to imitate a complicated "force field." To find out which areas of the brain manage the new information, the scientists used positron emission tomography to map blood flow in the subjects' brains as their muscles learned, and later recalled, how to compensate for the force field. Areas with the greatest blood flow are presumably the most active.
As the subjects initially learned the task, the region of the brain called the prefrontal cortex--known to be involved in short-term memory and many kinds of learning--was relatively active. And it stayed active as long as the subjects practiced the movement, even if they repeated it effortlessly hundreds of times. When the subjects returned 5 1/2 hours later, they had no trouble retracing the movements. But different parts of their brain had taken charge: the premotor, the posterior parietal, and the cerebellar cortex structures--regions that help control movement.
The intriguing implication, says neuroscientist Jerome Sanes of Brown University, is that although we are not aware of guiding individual muscles, conscious parts of the brain may be teaching them new tricks. "No one really understands how we learn to tie our shoes or play tennis," he says, or whether the brain processes involved are the same or different from learning other skills.