PTSD is seen most often in soldiers who have been in war zones
Scientists say they are moving ever closer to being able to diagnose Post Traumatic Stress Disorder (PTSD) using a brain scanner.
Research to be presented to the World Psychiatric Association congress in Florence suggests differences in the brain activity of PTSD sufferers.
Over 40 US soldiers who had served in Iraq or Afghanistan were tested - about half of whom had a diagnosis of PTSD.
Their brains were examined with an MRI scanner as they performed memory tests.
The term PTSD is used to describe a range of psychological symptoms people may experience following a traumatic, usually life-threatening, event. It is seen most commonly in those who have been on active service.
Researchers at Duke University in the US presented 42 soldiers, both male and female, with photographs of three similar faces.
They were then showed pictures of a combat scene, a non-combat scene - such as as man playing a trombone for instance - or a digitally scrambled picture.
Finally, they were shown a photograph of a face again and asked whether they had just seen it.
Driven to distraction
While watching the part of the brain associated with paying attention, researchers noted the group without PTSD was far more distracted by the pictures of combat scenes.
Those with PTSD were distracted by both the combat and non-combat pictures and performed more poorly in the memory test of faces which followed.
"This sensitivity to neutral information is consistent with the PTSD symptom of hypervigilance, where those afflicted are on high alert for threats and are more distracted by not only threatening situations that remind them of the trauma, but also by benign situations," said Dr Rajendra Morey, an assistant professor of psychiatry at Duke University.
"This has not been seen at the brain level before. If further research confirms this preliminary finding, this pattern could be useful in distinguishing the PTSD brain."
But experts in the UK said it was hard at this stage to see much practical use there was in being able to identify PTSD on a brain scanner.
"It is not actually hard to diagnose PTSD - all you need is a decent mental health professional," said Professor Simon Wessely, director of the King's Centre for Military Health Research.
"The real challenge is to persuade people to come forward for help.
"Neuroscience is clearly going to help us understand the neural substrates underlying symptoms, but as long as soldiers continue to believe that admitting to psychological distress is not what a soldier should do, most will never get near an MRI scanner."
Neil Greenberg, a senior lecturer in military psychiatry, said he could not see any therapeutic benefit in using a scanner to diagnose.
But he said: "There's a possible use from a medico-legal perspective, if someone wants to prove definitively that this is a condition they have.
"And it's also feasible that it could be used against those who are avoiding military duties because they say they have PTSD."