Left or right?
The findings of U. California-Berkeley researchers have lent insight into the neural process that controls which hand is chosen to complete everyday tasks, challenging previous assumptions about how motor-related decisions are made.
The study, published online Monday in the journal Proceedings of the National Academy of Sciences, found that magnetic stimulation of the brain can influence basic decisions, such as which hand to use when reaching for a tube of toothpaste, said Flavio Oliveira, a postdoctoral researcher in the campus psychology department and the lead author of the report.
When researchers applied magnetic stimulation to a right-handed subject’s left posterior parietal cortex – a region of the brain that is involved in spatial relations and movement planning – an increase in the use of the left hand occurred. This increase demonstrates both the causal relationship between the cortex and hand choice and the competitive nature of the decision-making process, Oliveira said.
By stimulating this region, the researchers were in essence “handicapping the right hand from winning the competition,” even if the normal preference of the test subjects was to use their right hands, Oliveira said.
“By and large, we typically think, ‘I choose to use my right hand,'” said Timothy Verstynen, a postdoctoral researcher in the department of psychology at the University of Pittsburgh and a contributor to the report. “But what this study found was that decisions like this are made at a more low level, a subconscious level. What we think of as an exercise of our conscious free will really isn’t so.”
The study revealed that the human decision-making process is more complex than previously imagined, Verstynen said.
“The existence of a competitive decision-making process is significant because it indicates the possibility of two times as many brain circuits to explore,” he said.
Although the researchers were restricted to focusing on hand choice – a basic, simple decision, Oliveira said – magnetic stimulation could potentially affect other choices.
“In theory, other more complex decisions could be influenced by such stimulation,” Oliveira said. “Do you decide to eat or get a glass of water? Which movie do you choose to watch? Which restroom do you go to?”
According to Oliveira, although the goal of the study was not to generate new rehabilitative methods, the findings may assist those who have lost the use of a limb and those with neurological disorders related to decision-making.
Verstynen described the study as a “teaser” study – one that will inspire more research on decision-making and free will.
“It’s a bit spooky, isn’t it? We can use brain stimulation to manipulate what we think of as a free, conscious decision,” he said.