DURHAM, N.C. -- Duke University researchers have shown how emotions such as fear or horror travel along separate paths through the brain and are more likely than simple distractions to interfere with a person's efforts to focus on a task such as driving.
Using functional MRI to watch human brains in action, the researchers showed that emotional stimuli and "attentional functions" like driving move in parallel streams through the brain before finally meeting up in a specific part of the brain's prefrontal cortex.
The results, published in the August 20 issue of The Proceedings of the National Academy of Sciences (PNAS), help explain why a person who suddenly feels a pang of emotion is especially likely to lose focus. They also may lead to new avenues of research for treating depression, attention-deficit disorder, post-traumatic stress syndrome and other disorders.
"We've known for a long time that some people are more easily distracted and that emotions can play a big part in this," said Kevin S. LaBar, assistant professor at Duke's Center for Cognitive Neuroscience and an author of the study. "Our study shows that two streams of processing take place in the brain, with attentional tasks and emotions moving in parallel before finally coming together." The two streams are integrated in a region of the brain called the anterior cingulate, which is located between the right and left halves of the brain's frontal portion and is involved in a wide range of thought processes and emotional responses.
LaBar and his colleagues used functional MRI devices to study the brains of neurologically healthy subjects who tried to pay attention to specific visual targets on a screen. The test subjects were distracted in various ways, sometimes by images that were likely to evoke an emotional response. The results confirmed previous findings that emotional stimuli are more likely to cause a person to lose focus. However, they also shed light on the long-standing mystery of how the brain juggles different kinds of signals, and how the signals travel.
The Duke study indicates that the brain segregates attentional and emotional functions into parallel streams that extend into the prefrontal cortex. Emotional processing tends to occur in the ventral, or lower, part of the brain's front, while attentional tasks occur near the top. Surprisingly, an increase in one type of function is accompanied by a noticeable decrease in the other.
"This study is part of our larger effort to identify parts of the brain that are associated with emotional processing," said Gregory McCarthy, director of the Duke-University of North Carolina Imaging and Analysis Center, who headed the research study. "These findings are important because diseases that involve distractability, from Alzheimer's to attention-deficit disorder, always seems to involve the prefrontal cortex. Understanding the biology of this will speed efforts to develop drugs or therapies that may influence these systems."
The research team is now carrying out a similar study with subjects diagnosed with clinical depression to see how their brain activity might differ. The study reported in PNAS was supported by the Department of Veterans Affairs, the National Institute of Mental Health, the National Alliance for Research on Schizophrenia and Depression and the Japan Foundation for Aging and Health.
Proceedings of the National Academy of Sciences
Duke-UNC Brain Imaging and Analysis Center
Kevin LaBar laboratory