NASHVILLE, Tenn. — Are you moody? If so, then there is a small area near the front of your brain an inch or two behind your right eye (if you are right handed) that is probably working overtime.
That is the conclusion of a new study, published Feb. 12 in the online Early Edition of the Proceedings of the National Academy of Sciences, which found a significant association between activity in a specific area of the brain and individual differences in mood.
There are lots of beliefs about the relationship of individual differences in emotional behavior and brain function, but this is one of the first times weve seen direct evidence of an association with a specific brain region, says David H. Zald, assistant professor of psychology at Vanderbilt University, who co-authored the paper with Dorothy L. Mattson from the Minneapolis Veterans Affairs Medical Center and José V. Pardo from the University of Minnesota.
The study used the brain imaging technique called positron emission tomography (PET) to record the levels of brain activity in two groups totaling 89 individuals. The subjects ranged in age from 18 to 55 years, with a median age in the mid-20s. There were slightly more men than women. None of the participants had a history of medical or neurological problems or were using mood-affecting medicines. They were all right-handed, because of potential differences in the brains of left- and right-handers.
Before the brain scans were taken, the individuals filled out a questionnaire that asked them a series of questions about the extent to which they had experienced unpleasant moods during the previous month. They then used these answers to rate each individual on a negative affect scale. Negative affect is a technical term that includes a range of unpleasant mood states, ranging from irritability to anxiety to anger. Previous studies have established the reliability of the negative-affect scale and have shown that individuals who rate high on the scale are at increased risk of developing depression or anxiety disorders.
After scanning the first group of 51 subjects, the researchers compared the levels of brain activity of all the subjects. They looked for areas where the activity level varied in accordance with patients rating on the negative affect scale, showing either increasing or decreasing activity levels in those with higher negative-affect ratings.
The most striking positive correlation we found was localized in only one small region of the brain, the ventromedial prefrontal cortex, says Zald. Because this is just a correlation, we dont know whether this activity is the cause or the effect of negative mood states. Such a connection does make sense, however, because animal studies show that this region of the brain controls heart rate, breathing, stomach acidity levels, sweating and similar autonomous functions that have a close connection to mood.
In order to double-check their findings, the researchers assembled a second group of 38 subjects. They put them through the same procedure and came up with essentially the same results: the variation of activity associated with differences on the negative affect scale account for about 20 percent of the total variation in the activity levels measured in the region.
Since the time of the ancient Greeks, there has been speculation that the brain is the basis of personality, but it is only within the last 20 years that scientists have developed instruments capable of measuring brain activity with enough accuracy to address this question directly.
With increased knowledge of the relationship between brain function and mood, we should be able to find more effective ways to treat the millions of Americans who suffer from clinical depression each year, says Zald.
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