Researchers at Yale University and the Icahn School of Medicine have identified biomarkers, using sophisticated computational tools, which may explain why some people have more severe posttraumatic stress disorder (PTSD) symptoms than others.

The findings published in Nature Neuroscience may help evaluate who would be at greater risk of PTSD symptoms.

The study of combat veterans who had been exposed to extreme incidents, demonstrated that those veterans who had severe PTSD symptoms had distinct patterns of neurological and physiological responses affecting associative learning—the ability to discern harmful stimuli from safe ones in the environment.

Ilan Harpaz-Rotem, associate professor of psychiatry at Yale and co-corresponding author of the paper said, “We are shedding new light on how people learn fear and unlearn it.”

The researchers wanted to unravel why some people suffer greatly when experience a traumatic event while others exhibit few or limited side effects.

Retired soldiers who had undergone intense circumstances during combat deployment were examined for physiological responses while being presented with pictures of two different faces. In classic fear-conditioning tests, the subjects were given slight electric shocks after viewing one of the faces, but not the other. Later, the faces that were combined with shock were switched in an attempt to have the subjects “unlearn” original fear conditioning and test their ability to learn that something new in the environment is hazardous.

The findings deduced using computational modeling revealed that in people with severe PTSD symptoms, the amygdala and striatum were less able to track changes in threat level, which may serve as biomarkers for PTSD symptom severity.

According to Harpaz-Rotem, “There were pronounced variances in the ‘learning rates’ of those with severe symptoms and those without symptoms.” Highly symptomatic individuals tended to overreact to a mismatch between their expectations and what they actually experienced. In a war zone, a garbage can might contain an explosive device, he explained, but those with severe PTSD symptoms have a harder time unlearning the fear in civilian life in comparison to those with less severe symptoms.

The study’s co-author and associate professor of comparative medicine and neuroscience at Yale, Ifat Levy said, “The study has offered novel understanding of the neurobiology of PTSD and a better understanding of learning processes among people with this disorder which might pave the way for refining potential PTSD treatment in future.

PTSD is a common anxiety disorder that develops after exposure to a harrowing event or ordeal. It can occur at any age between childhood and adulthood. Those suffering from PTSD may experience startling thoughts and memories of the event. Sleeplessness, depression, or other anxiety disorders frequently co-occur with PTSD.

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doi:10.1038/s41593-018-0315-x

 

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