Following the attacks on Sept. 11, 2001, research has broadened the understanding of post-traumatic stress disorder, U.S. researchers say. A special issue of the American Psychologist includes a dozen peer-reviewed articles, which examine the social, political and psychological impacts of the nation's worst terrorist attacks. The issue illustrates how psychology is helping people understand and cope with Sept. 11, 2001's, enduring impacts and explores how psychological science helped people understand the roots of terrorism and how to prevent further attacks. For example, Yuval Neria of Columbia University and New York State Psychiatric Institute, Dr. Laura DiGrande of New York City's Department of Health and Mental Hygiene and Ben G. Adams of Columbia University examined the research literature on PTSD among highly exposed populations. "The terrorist attacks of Sept. 11, 2001, brought a substantial and enduring burden of post-traumatic stress disorder on those people who lost loved ones, as well as on firefighters and recovery workers," the study says.