July 21, 2005 — Individuals who cope well with stress after trauma usually are described as being "thick skinned," but new research reveals the thickness is in their brains, not in their skin.

Scientists determined that resilient people tend to have a thick ventral medial prefrontal cortex (vmPFC), which is near the front of the brain. Conversely, this region tends to be thin for those who experience a lot of anxiety.

The discovery will enable doctors to predict who is at risk for stress-related disorders, which could lead to better treatments and may even determine who is best suited for certain careers and activities.

"For instance, an individual with a thin vmPFC might wish to avoid high risk professions such as policeman, firefighter or soldier," said Scott Rauch, co-author of the study, which recently appeared in the Proceedings of the National Academy of Sciences.

Rauch, who is associate chief of psychiatry for neuroscience research at Massachusetts General Hospital, and his colleagues made the determination after testing 14 healthy volunteers.

Volunteers looked at digital photographs of furnished rooms that contained lamps. Whenever the lamps lit up in colors, the test subjects would receive an electrical shock that each participant previously rated as "highly annoying but not painful."

A monitor measured skin moisture levels, or flop sweat, released during this fear-conditioning test.

The volunteers then underwent a "fear extinction" process, where they saw the same photos and lights, but received no shocks. This shockless test was repeated while the volunteers had an MRI brain scan.

The scan results then were compared to the skin moisture readings, which enabled the researchers to link the brain images to anxiety levels.

The MRIs revealed that volunteers whose conditioned fear of the flashing lights diminished during the fear extinction test phases each had a thick vmPFC.

Gregory Quirk, associate professor of neuroscience at Ponce School of Medicine in Puerto Rico, has performed similar MRI research on rodents.

"This finding is extremely important because it builds on data from rodents indicating that individual variability in fear responses is correlated with activity levels of neurons in the prefrontal cortex," Quirk told Discovery News.

When thick, this part of the brain appears to function like a fear helmet that protects against stress.

"Increase in the size, number or connections of neurons within the ventral medial prefrontal cortex may allow this particular brain region to have stronger inhibitory influence on brain regions that generate the conditioned fear responses in the first place," Rauch said.

The test mirrored what happens to people who experience trauma and then undergo therapy. For example, a person attacked in an elevator might later fear elevators.

Repeated exposure to elevators without any threats gradually extinguishes the fear in most victims, but some people have trouble recovering their sense of calm. These individuals, according to the research, may have a thin vmPFC.

Rauch and his team currently are awaiting the completion of analogous studies on people who are known to suffer from anxiety disorders.

Quirk also hopes the researchers will measure vmPFC activity levels to better reveal how the coping mechanism does or does not work properly.