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Oct. 21, 2008

NORTHAMPTON, Mass. – A study that tracked police cadets from training through induction into the force is the first to report that people who show exaggerated startle responses while being threatened with harm may be more likely to develop posttraumatic stress disorder (PTSD).

Researchers studied 138 police academy cadets, both men and women, who were in training in urban academies in New York and California, and found that cadets who were more easily startled were also more likely to develop symptoms of PTSD once on the force for a year.

PTSD affects about 7.7 million American adults age 18 and older, according to the National Institute of Mental Health (NIMH) and is especially likely to occur following interpersonal violence. Given the violent nature of their work, urban police officers are about twice as likely as civilians to develop the disorder. Yet, mere exposure to violence and traumatic stress is not enough to predict who will get PTSD.

“We need to find out who is likely to head down this path, particularly among those who put themselves in harm’s way,” said Nnamdi Pole, Smith College associate professor of psychology and the study’s lead researcher. “If we can help figure out a vulnerability in advance, we can help those at risk to avoid going down that path.”

Pole conducted the study with colleagues at the University of California, San Francisco, and funding from the NIMH. It is slated for publication in the journal Biological Psychiatry.

Long before PTSD was a recognized psychiatric diagnosis, distressed trauma survivors complained about being easily startled, according to Pole. Though the understanding of PTSD has changed in many ways over the years, “exaggerated startle” has remained on the list of core symptoms.

This investigation — part of a new push to study people who are the likeliest candidates for PTSD (prospective) as opposed to people who already have PTSD (retrospective) – indicates exaggerated startle may be more than just a symptom of PTSD but also an early warning system, or risk factor, for PTSD.

To trigger the startle effect, study participants wore headphones that did not provide any sound until an unexpected moment when they gave off a sudden loud noise. In the seconds following that burst of noise, researchers measured participants’ eye blinks, heart rate and sweat responses. Importantly, participants heard several startling sounds while also maintaining an awareness of an approaching threat, which in the study was a mild electric shock.

Researchers gathered the participants together again one year later – a year into their exposure to police-related trauma – and identified two significant findings. Those who had exhibited the strongest startle reactions while anticipating threat of shock and those who were unable to moderate their physiological responses after repeated startles were more likely to exhibit symptoms of PTSD after a year of police work.

Given the findings, said Pole, eventually science may be able to assist those with a propensity for PTSD to either avoid risky careers or perhaps to strengthen the vulnerabilities revealed by the startle testing so that future officers may function optimally in high risk environments. 

The research team which, in addition to Pole, includes Thomas C. Neylan, Christian Otte, Clare Henn-Hasse, Thomas J. Metzler and Charles R. Marmar, will continue to gather data throughout the police officers’ first five years of service during which time the officers’ rate of PTSD is expected to rise.


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