Choosing when to schedule a doctor's appointment or whether to fasten your seatbelt might not seem like emotional tasks, but a new study suggests that in fact people use the emotional part of the brain to make rational decisions for themselves. The findings, presented yesterday at the annual meeting of the Radiological Society of North America, lend weight to the notion that the emotional and rational parts of the brain may overlap more than previously thought.

Dean Shibata of the University of Washington posed a series of personal and impersonal questions to 11 test subjects, requesting that they mull the questions over for a few seconds while MRI scanners measured their brain activity. "The point was to test the hypothesis that when people make decisions that affect their own lives, they will utilize emotional parts of the brain, even though the task itself may not seem emotional," Shibata explains. In the case of the seatbelt decision, for example, "that seems like a very rational kind of thing," he remarks. "But it's also very emotional¿you can envision that you are going to die, that you could hit your head on the windshield, if you don't put your seatbelt on." As it turns out, people making these kinds of so-called personal rational decisions exhibited activity in the ventromedial frontal lobe¿the part of the brain that governs emotion. In contrast, those thinking impersonally about, say, the comparative financial costs of two events, displayed no such brain activity.

The research results fit neatly with earlier work suggesting that patients who have sustained damage to the emotional part of the brain can solve abstract problems but struggle with personal rational decisions. Looking forward, Shibata expects that the work could lead to insights into mental illnesses as well. "Hopefully by understanding how our rational and emotional sides come together, we can understand more about psychiatric diseases such as schizophrenia, and ultimately how to treat them."