A region of the brain a few inches behind the bridge of the nose may hold the key to why some people have a negative outlook on life, scientists announced last week.
The study, published in the Proceedings of the National Academy of Sciences, is the first to examine the neurological roots of what scientists call "negative affect," a trait that predisposes people to anxiety, irritability, anger and a range of other unpleasant moods.
By suggesting that an unconscious disposition toward these emotions may be molded by a specific area in the brain, the research moves into previously uncharted waters. It is part of a broad effort by neuroscientists to use powerful brain imaging technology to pinpoint the areas of the brain responsible for various emotions.
"It touches on an important issue: the relationship between individual differences in personality and brain function," said Marcus Raichle, a professor of radiology and neurology at Washington University in St. Louis. "There have been for many, many years attempts to explain the differences we observe among ourselves--[why] we have different personalities.
"If you believe behavior and brain are related, you would have to suppose there are differences in brain systems that lead to differences in personality," he said.
For the study, scientists at Vanderbilt University, the Veterans Affairs Medical Center in Minneapolis and the University of Minnesota asked 89 healthy people to take detailed tests that measured their emotional outlook over the previous month. The tests were designed to screen out people's mood states on the day they were evaluated and look instead for a pattern of emotional attitudes--in other words, an outlook or a temperament.
While the subjects rested after the tests, the researchers conducted brain scans that measured changes in blood flow within their brains. The scientists found that increased brain activity in one particular region--the ventromedial prefrontal cortex--was associated with those who reported greater negative affect.
Many factors besides physiology are responsible for personality, and other parts of the brain are involved in emotions. But researchers say the circumstantial evidence indicates that the ventromedial prefrontal cortex acts as a sort of volume knob for emotions. While the emotions may be produced elsewhere in the brain in response to stimuli, this region of the brain can make them deafening or muted.
As a result, some people may react sharply in a situation, while others appear unruffled. The volume knob, in other words, may be what people interpret as temperament.
Most studies of brain activity have focused on trying to match regions of the brain with particular moods or such abilities as vision, language and physical movement. By focusing on an underlying trait or a temperament in healthy people, scientists hope to eventually understand why healthy people react so differently to the same cues and why people with mental illnesses have extreme responses.
In turn, this could lead to better treatments of both psychiatric medicines and psychological therapy. Current treatments for these emotional disorders may in fact work by affecting these same brain areas.
"There's at least one component of the biology of temperament in the ventromedial prefrontal cortex," said Jose Pardo, an associate professor of psychiatry at the University of Minnesota and one of the researchers who conducted the study. "In a practical sense, what we know is a person with higher activity in this area can be predicted to have a high level of negative affect," he said. "High levels of negative affect have been shown to have a high risk of depression and anxiety. This may begin to tie aspects of temperament to disease."
While negative affect may seem like the opposite of positive affect, researchers do not find that people with diminished activity in this part of the brain are "happier." Instead, patients with damage to the ventromedial prefrontal cortex have previously been found to lack normal responses to emotional cues, according to the paper.
"What you see in people with brain lesions in this area is they don't seem to be able to appreciate risk," said David Zald, an assistant professor of psychology at Vanderbilt and the lead author of the study.
"They can tell you they are doing something that has a good chance of failing, but they don't have the emotional reaction to it--they don't have visceral arousal."
For example, he said, "if you are betting a lot of money, you may get a feeling in the pit of your stomach. They won't experience that; they won't get as upset about it."
The example serves notice to those who might want scientists to find a way to shut off the brain region in order not to be bothered with anxious or irritable thoughts.
"Anxiety is often helpful to us; it is protective,'' said Zald. "If you don't have it, you're likely to not detect when you are in danger or when you are taking too big a risk."