Threat bias interacts with combat, gene to boost PTSD risk

Soldiers preoccupied with threat at the time of enlistment or with avoiding it just before deployment were more likely to develop post-traumatic stress disorder (PTSD), in a study of Israeli infantrymen. Such pre-deployment threat vigilance and avoidance, interacting with combat experience and an emotion-related gene, accounted for more than a third of PTSD symptoms that emerged later, say National Institutes of Health scientists, who conducted the study in collaboration with American and Israeli colleagues.

"Since biased attention predicted future risk for PTSD, computerized training that helps modify such attention biases might help protect soldiers from the disorder," said Daniel Pine, M.D., of the NIH's National Institute of Mental Health (NIMH).

Pine, Yair Bar-Haim, Ph.D., of Tel Aviv University, and colleagues, report their findings, Feb. 13, 2013, in the journal JAMA Psychiatry.

Bar-Haim's team tracked 1085 male Israeli soldiers from recruitment through combat deployment during 2008-2010, to pinpoint how shifting attitudes toward threat interact with other factors to predict symptoms that develop after exposure to dangers. They expected that the more soldiers paid attention to avoiding threats just before and during deployment, the more they would suffer PTSD symptoms.

Researchers measured threat attention biases over the course of soldiers' first year of service: at the time of recruitment, about six months later – just before deployment to combat – and six months after deployment. Data from all three time points was collected for 487 of the soldiers.

Soldiers performed a computerized task that required paying attention to locations of neutral words, such as "data" or threatening words, such as "dead." A faster reaction time for identifying the location of threat words indicated increased threat vigilance. Slower reaction times to such word locations indicated attention away from threat, or threat avoidance.

The study also examined how threat attention bias vulnerability might be moderated by other factors, including the gene that codes for the protein on neurons that recycles the brain chemical messenger serotonin from the synapse. Versions of this serotonin transporter gene had been previously linked to PTSD risk. Evidence suggests that people with gene versions that result in less efficient recycling may be overly vigilant toward threats under normal circumstances. Yet there is also evidence that having these low-efficiency versions may help people cope with dangerous conditions, when such heightened vigilance may be adaptive.

As expected, soldiers who experienced higher combat exposure – e.g., served in units operating outside Israel's security fence – tended to show more threat vigilance than those with less stressful assignments. Compared to soldiers who were neither vigilant nor avoidant, soldiers with greater vigilance at recruitment or avoidance at six months – on the eve of deployment – had more PTSD symptoms at the end of their first year of service.