John Violanti -- associate professor of social and preventive medicine in the University at Buffalo's School

of Public Health and Health Professions -- said chronic and severe stress is thought to decrease blood flow between emotional and thinking areas of the brain, leading to lingering memories and thoughts of stressful experiences.

"This can, in turn, lead to shrinkage of the hippocampus, an area of the brain that involves memory and extinction of fear," Violanti said Friday in a release.

Violanti, a former member of the New York Police Department, is principal investigator on a pilot study of PTSD in police officers. The study is funded by the National Institute of Occupational Safety and Health.

"Our aim is to assess the association of PTSD symptoms and changes in brain function and structure in police officers, a group routinely exposed to traumatic work situations," he said.