Right or Left Hand Actions – It Depends on the Brain

Scientists have found that brain stimulation can change what hand you use most, thanks to magnetic pulses, which can disrupt the neurons that control motor skills.

About 80 percent of people worldwide are right-handed, but when it comes to performing a task that does not require precision, most people are ambidextrous.

Inside the human brain, there is a battle every time we want to push a button or reach for a glass of water, because the brain races to decide which hand, the right or the left, will do the job.

University of California, Berkeley researchers found out that if a certain region of the brain receives magnetic stimulation, then the left side is more likely to win.

They used transcranial magnetic stimulation, or TMS, to the posterior parietal cortex region of the brain in 33 right-handed volunteers.

The results showed that stimulating the left side triggered an increase in their use of the left hand.

The participants had sensors on their fingertips, and they were instructed to reach for different targets on a virtual tabletop while a 3-D motion-tracking system followed the movements of their hands.

When researchers stimulated the left posterior parietal cortex, and the object was located in a spot where they could use either hand, there was a significant increase of the use of the left hand, said Flavio Oliveira, a UC Berkeley postdoctoral researcher in psychology and neuroscience and lead author of the study.

The motor skills of the right side of the body are controlled by the left hemisphere of the brain and the other way around for the left side of the body.

The parietal cortex plays a very important part in processing spatial relationships and movement planning, so when it is stimulated, the neurons that govern motor skills are disrupted.

“You're handicapping the right hand in this competition, and giving the left hand a better chance of winning,” Oliveira said.

This research is opening a way for clinical advances in the rehabilitation of victims of stroke and other brain injuries.

"By understanding this process, we hope to be able to develop methods to overcome learned limb disuse," said Richard Ivry, UC Berkeley professor of psychology and neuroscience and co-author of the study.

The research was published in the journal Proceedings of the National Academy of Sciences.