According to a new brain study, even people who seemed resilient but were close to the World Trade Center when the twin towers toppled on Sept. 11, 2001, have brains that are more reactive to emotional stimuli than those who were more than 200 miles away.

That is the finding of a new Cornell study that excluded people who did not have such mental disorders as post-traumatic stress disorder (PTSD) or major depression. One of the first studies to look at the effects of trauma on the brains of healthy people, it is published in the May issue of the journal Emotion.

"These people appear to be doing okay, but they may, indeed, be having more sensitive responses to upsetting stimuli," said Elise Temple, a co-author and assistant professor of human development at Cornell.

More than half the population experiences trauma, which makes people more likely to develop PTSD, depression, anxiety and physical illness later in life, according to other studies. Also, trauma has been found to make the brain's emotional processing centers -- particularly the amygdalae, the parts of the brain that judge emotional intensity and make emotional memories -- more sensitive in cases of PTSD.

The findings suggest that events that trigger shock, fear and horror that are within a normal range -- may cause similar changes in the brain that traumas do. Victims may experience lingering symptoms (bad dreams, jumpiness, thinking about the incident and avoiding the site of the trauma), but they are not severe. However, the kinds of changes that these traumas cause in the brain, the researchers suspect, create vulnerability to developing future mental disorders.

Specifically, the Cornell researchers found that three years after Sept. 11, 2001, the amygdalae were most sensitive in those who were close to the World Trade Center. These individuals tended to still experience lingering symptoms that were not severe enough to be diagnosed as a mental disorder. Those with lingering symptoms showed significantly more sensitive emotional reactions in the brain when stimulated by photographs of fearful faces.

"Our study suggests that there may be long-term neural correlates of trauma exposure, even in people who have looked resilient," said lead author Barbara Ganzel, Cornell M.S. '99, Ph.D. '02, a postdoctoral researcher in human development at Cornell. "Up until now, there has been very little evidence of that."

Using functional magnetic resonance imaging to see how people's brains responded to photographs of fearful versus calm faces, the scans of 11 people who were within 1.5 miles of the World Trade Center on Sept. 11, 2001, were compared with those who were living more than 200 miles away at the time; none of the subjects had psychiatric disorders.

"We know that looking at fearful faces in normal adults tends to activate the amygdalae relative to looking at neutral faces," said Ganzel. "So we were looking to see if people who have had a very bad experience would have more response to this relatively mild everyday stimulus."

Indeed, the amygdalae of those who were close to the twin towers were significantly more activated than that of others, even when other factors were controlled for in the analysis.

"People who had experienced traumas that left them with more lingering symptoms were the ones who had higher activity in their fear centers," said Temple. "We think that the World Trade Center experience was traumatic enough that it left them with hyperactive amygdalae."

Other co-authors include B.J. Casey, director of the Sackler Institute for Developmental Psychobiology at the Weill Cornell Medical College; Henning Voss, a physicist at the CitiGroup Biomedical Imaging Center in New York City, where the fMRI scanning took place; and Gary Glover of Stanford University, who developed the fMRI techniques used.