Post-traumatic stress disorder may change brain processes that make it harder to recognize fear and sadness, Bosnia-Herzegovina and Dutch researchers say.Dr. Ervin Poljac of the International University of Sarajevo and the University of Leuven, Dr. Barbara Montagne of the Radboud University Nijmegen Medical Centre and Edward de Haan from the University of Amsterdam, investigated emotional processing in a group of war veterans with symptoms developed after prolonged exposure to combat-related traumatic events.PTSD is already known to be associated with difficulties in experiencing, identifying, and describing emotions, but this study examined the participants\' ability to recognize particular emotional facial expressions, the researchers say.Participants were shown short video clips of emotional faces representing one of the six basic emotions -- happiness, anger, fear, surprise, disgust and sadness.Compared with healthy subjects, the participants with PTSD were less able to recognize two emotions in particular: fear and sadness, the study says.The findings are to be published in the September issue of Cortex.