Babies are born with a natural preference for using their left or right side. Now, a new study suggests that preference alone doesn’t explain the dominant side’s superior skills: They come from practice.
The results, published June 30 in the Proceedings of the National Academy of Sciences, show how flexible human brains can be when learning new motor skills. A deeper understanding of how the brain generates movements could help illuminate what happens when that process goes awry, such as after a stroke.
Even before birth, babies tend to move one hand more than the other, an early sign of whether a person will be left- or right-handed. This preference probably comes from a mix of genetics and quirks of brain development. But this origin story isn’t what interested researchers. Instead, they wondered why a person’s dominant side — left or right — is more talented.
It could be that one half of the brain is just better at controlling movement. Or, as neurologist and neuroscientist Ahmet Arac now suspects, it could all come down to practice.
To tease these two ideas apart, Arac and his colleagues had 11 people write the letter A and the number 8 with either their dominant or nondominant hand. The results were exactly what you’d expect; dominant hands wrote the figures better.
Then, Arac, of the David Geffen School of Medicine at UCLA, and his colleagues threw these folks a curveball by asking them to write with a pen taped to an elbow. Half the people wrote with their dominant elbow, and the other half wrote with their nondominant elbow. Neither elbow — dominant or nondominant — was very good.
Yet practice made all the difference. After a new group of 12 people put pen-equipped elbow to paper for a few hours, their writing improved — and it improved equally for both dominant and nondominant elbows. By finding symmetrical improvements in the elbow, the new study helps make the case that practice matters. Dominance, the researchers write, “is a practice effect.”
Most of the participants were right-handed. A study focused on lefties would be interesting, Arac says, as would exploring different sorts of body movements. Scientists also want to understand “what enables better or faster learning,” Arac says, particularly for people as they relearn certain movements.
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