TUESDAY, July 12, 2005 (HealthDay News) -- It may not be thick skin that protects you from emotional pain, but a thick brain.
Scientists have discovered that variations in the size of an area of the brain called the ventromedial prefrontal cortex may explain why some people recover from trauma better than others. Specifically, people with a thicker ventromedial prefrontal cortex (vmPFC) exhibited better ability to inhibit fear.
The research, which appears in this week's issue of the Proceedings of the National Academy of Sciences, may be an important clue in the age-old mystery of why some people react severely and continuously to emotional trauma while others don't.
There may be numerous clinical implications to the research, the study authors said.
"One would be the idea that perhaps people with a thinner cortex in this area might be at greater vulnerability for developing anxiety disorders, but that's still a speculation," said senior study author Dr. Scott Rauch, director of the Psychiatric Neuroscience Research Division at Massachusetts General Hospital, in Boston. "This could also be a potential predictor of responses to [certain types of] behavior therapy."
Some people associate certain cues with traumatic memories so that, when they are exposed to the cue, the memory comes flooding back. In other words, certain sounds or sights trigger a recall of the previous, traumatic experience. The most obvious example of this is post traumatic stress disorder (PTSD).
For most people, this sensitivity diminishes over time and the fearful response goes away, something called "extinction memory."
For others, however, the fear persists.
Earlier animal and other studies had indicated that the vmPFC, on the lower surface of the brain, might be involved in this process.
To see if individual differences in fear extinction correlated to vmPFC size, the study authors recruited 14 healthy volunteers. On the first day, each person was given photos to look at, and then an electric shock. Then they viewed the photos without the shock.
The next day, the volunteers looked at the same photos while researchers monitored changes in electrical activity in the skin -- an indication of anxiety level. The participants then underwent brain scans with structural magnetic resonance imaging.
Those who had smaller skin responses -- in other words, less anxiety -- also had a thicker vmPFC, the researchers said.
"This was the only region in the brain that showed the significant relationship to extinction memory," said study author Mohammed Milad, a research fellow in the department of psychiatry at Massachusetts General Hospital.
Although the finding is an important one, many questions remain, said Paul Sanberg, director of the University of South Florida Center for Aging and Brain Repair, in Tampa.
For instance, do some people just have a thicker vmPFC and, therefore, a better ability to recover from trauma, or is the ability to cope with stress acquired? Some studies have shown the brains of people and animals tend to get bigger in a mentally stimulating environment, Sanberg said.
It's also not clear what mechanisms are at work in that region of the brain, Sanberg said. "Is it more neurons or more glial cells, is it connections, or is it the neurochemistry?" he asked.
Rauch said, "The most obvious connection [of the research] would probably be to PTSD, but we believe it certainly has implications for panic disorder and potentially for other anxiety disorders such as phobias."
The research may have broader implications for treatment, he added. "All of those anxiety disorders are responsive to extinction-based behavior therapy," Rauch said.
Dr. Rodrigo Kuljis is a professor of neurology and psychiatry at the University of Miami School of Medicine. He said the new research "is interesting. It tends to support the feeling that certain aspects of memory are mediated by certain parts of the brain. It could be used eventually as a measure to determine if someone is more susceptible to certain conditions and also to predict treatment."
The real question, Kuljis said, is whether the new findings can be corroborated. "It's very sophisticated imaging but the bottom line is you are measuring something [the vmPFC] that is around a centimeter thick at best, probably thinner," he said. "The resolution of the instrument is marginal, but it's the best we have. The margin of error is enormous."
More information
To learn more about post-traumatic stress disorder, visit the National Center for PTSD.
