By forcing people to write with their elbows, scientists discovered that repetition really matters
Babies are born with a natural preference to use their left or right side. Now, a new study suggests that preference alone doesn’t explain the dominant camp’s superior skills: they come from practice.
The results, published on June 30 in the Proceedings of the National Academy of Sciences, show how flexible the human brain can be when learning new motor skills. A deeper understanding of how the brain generates movements could help better understand what happens when this process goes awry, such as after a stroke.
Even before birth, babies tend to move one hand more than the other, an early sign that 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 is not what interests researchers. Instead, they asked why a person’s dominant side – left or right – is more talented.
It could be that one half of the brain is simply better at control the movement. Or, as neurologist and neuroscientist Ahmet Arac now suspects, it could all come down to practice.
To differentiate these two ideas, Arac and his colleagues asked 11 people to write the letter A and the number 8 with their dominant or non-dominant hand. The results were exactly what you expected; dominant hands wrote numbers better.
Then Arac, of the David Geffen School of Medicine at UCLA, and his colleagues challenged these people by asking them to write with a pen taped to their elbow. Half of the people wrote with their dominant elbow and the other half with their non-dominant elbow. Neither elbow – dominant or non-dominant – was very good.
However, practice made all the difference. After a new group of 12 people put pen-equipped elbows to paper for a few hours, their writing improved – and it improved equally for both dominant and non-dominant elbows. By finding symmetrical improvements at the elbow, the new study helps demonstrate that practice is important. Domination, the researchers write, “is a practice effect.”
Most participants were right-handed. A study focusing on left-handers would be interesting, Arac says, as would exploring different types of body movements. Scientists also want to understand “what enables better or faster learning,” says Arac, especially for people who are relearning certain movements.
