Left or right – which hand do you prefer?

Right-handed people use their left hand more when the left hand side of the brain is stimulated say scientists from University of California Berkley.

Researchers applied transcranial magnetic stimulation (TMS) – magnetic pulses which alter electrical activity in the brain and disrupt neurons in the underlying brain tissue – to the posterior parietal cortex of the brain in 33 right-handed volunteers. They found that stimulating the left side of the brain increased the use of their left hand.

Participants – with sensors on their fingers – were asked to reach for various targets on a virtual tabletop while a 3D motion tracking system followed the movement of their hands. When the left posterior parietal cortex was stimulated and the target was located in an area when both hands could be used, there was a significant increase in the use of the left hand.

“You’re handicapping the right hand in this competition and giving the left hand a better chance of winning,” said Flavio Oliveira, a postdoctoral researcher and lead author of the study.

The study’s findings challenge previous assumptions about how we make decisions revealing a competitive process for completing manual tasks. The left hemisphere of the brain controls the motor skills of the right side of the body, and vice versa, but by stimulating the parietal cortex – which plays a role in processing spatial relationships and planning movements – the neurons that govern motor skills are disrupted.

TMS is able to manipulate the brain to change plans for which hand is used to do the task, and may help forward research in rehabilitation of stroke and other brain injury. The research was inspired by alien hand syndrome, a neurological disorder in which victims report the involuntary use of their hands.

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