However, brain scans of 11 healthy adults shows the part of the brain that records emotions was much more active when decisions affected the subjects personally than when the decisions had little impact on their lives.
"There was a clear dichotomy. The ventromedial frontal lobe was much more active in personal as opposed to objective decision-making," says Shibata.
The study involved six women and five men who were asked a series of questions designed to elicit either emotional or objective responses. One emotional question, for instance, was whether you would rather have a camera or a bicycle. Then, to elicit an objective response, participants were asked which costs more, a camera or a bicycle.
"The questions were as close as possible, but different. One was about desire and the other about cost," Shibata says.
A functional magnetic resonance imaging (fMRI) machine showed high activity in the ventromedial frontal lobe (the part of the brain typically involved in emotions) when participants were making their choice. Activity in the same brain section was minimal when they were figuring out the cost. The magnetic scanning technique highlights blood flow and oxygen use in the brain.
"When we make a [personal] decision, we get in our brain an emotional image of the outcome of that decision," like imagining sloppy work if we don't sharpen a pencil, Shibata says.
Without that imaging, Shibata says it appears very difficult to make the decision about something that directly affects us.
Shibata says his findings corroborate other recent research that show emotional and analytical thinking are closely intertwined in personal decision-making.
For instance, he says other research shows that people with injury to the ventromedial front lobe through stroke or tumors have a very difficult time making the simplest decisions about themselves, like scheduling a doctor's appointment.
"You can give them a psychological test, and they will do quite well. Their intelligence and memory are intact, but they have a striking inability to narrow down the possibilities. In the absence of emotional drive, they don't have the basis to make a decision [about themselves]," he says.
Shibata says he hopes continuing research in this area eventually will have clinical use in treating diseases like schizophrenia.
"As we understand more about how the normal brain works and how emotions are processed, we can understand what's different about the brains of schizophrenics. Then we can use the information to better intervene," he says.
For instance, doctors could monitor brain activity while a patient takes certain drugs to understand how the drugs are working and thus be able to more specifically target which drugs are most effective in which patients.
"There are many different techniques used to evaluate how patients make decisions, and it's difficult to draw direct conclusions from a single piece of imaging data," says Michael Nolan, an anatomy and neurology professor at the University of Southern Florida College of Medicine.
What To Do
A description of schizophrenia can be found at the University of Groningen Web site. If you'd like to volunteer to take a decision-making test for research, go to California State University.
Check here for more on how the brain works and how illusions can fool your mind.