PTSD typically occurs in the wake of a traumatic event--anything from illness to an earthquake to witnessing a shooting--and its symptoms are anxiety, depression, sleep disorders and flashbacks. Naomi Breslau, an epidemiologist at Michigan State University and the lead author of the study published in the November issue of Archives of General Psychiatry, says that when researchers first encountered the connection between intelligence and PTSD, while studying Vietnam veterans, "the idea was that it was the PTSD that caused a reduction in IQ." Subsequent studies, including her team's, however, showed that to be untrue: "It wasn't low IQ, but it was high IQ that came up as an important factor," she explains. "High IQ is protective, rather than lower IQ is a risk factor."
In the new study, Breslau's team studied 336 boys and 377 girls born in one of two hospitals: one located in a suburban area and another in an impoverished urban neighborhood, where traumatic events are more likely to occur. At six years of age, each child took a standard IQ test that resulted in a mean of 100 and standard deviation of 15. In addition, the children's teachers evaluated them on their conduct at school, while the researchers interviewed parents to ascertain whether the kids showed any signs of anxiety-related behavior, such as irrational fears. When the children reached 17 years of age, Breslau's team probed each subject to determine what, if any, trauma they had suffered over the previous 11 years as well as what effects it may have had on them.
Of the 713 study participants, nearly 76 percent had suffered through at least one traumatic event, and more than 8 percent of those subjects presented symptoms of PTSD. Those teens who were found to have had behavioral issues as children were nearly three times more likely to have experienced trauma and twice as likely to have PTSD than those who exhibited good conduct. Urban children were more than three times more likely than their suburban counterparts to experience trauma and nearly twice as likely to suffer from PTSD. However, those with an IQ higher than 115--one standard deviation above the mean--were only 30 percent as likely to have faced a traumatic event and were only 20 percent as likely to have PTSD. In fact, this protective aspect of IQ to trauma and PTSD was consistent even if a child grew up in an urban area or had behavioral issues.
High IQ is a solid predictor of education-related abilities as well as socioeconomic success, says Breslau, who speculates that higher intelligence may also confer the ability to avoid "getting into trouble." The low incidence of PTSD among more intelligent kids, she adds, could be tied to advanced coping with any sort of exposure to severe occurrences. It is "the way that people explain to themselves what happened to them, how it fits in with their lives, whether it is their fault or not their fault, whether they can get over it and perform some task," Breslau says. "There is no question that there are cognitive aspects with the disorder."