A current theory holds that during a traumatic event, a person may learn to associate the people, locations, and objects in the situation with the trauma, and long after the event even the “safe” stimuli can trigger fearful and defensive responses. Experts believe it is an “overlearned response” to a threatening experience. But the way in which that learning happens is not well understood, say researchers from Yale University in New Haven, Connecticut, and the Icahn School of Medicine at Mount Sinai in New York City. Their study, though, may shed new light on how people with PTSD symptoms learn and unlearn fear.
In the study, funded in part by the National Institute of Mental Health, the researchers examined how the mental adjustments performed during learning and the way the brain tracks these adjustments relate to symptom severity.
They gave combat veterans with varying levels of PTSD symptom severity a reversal learning task. Participants were shown 2 mildly angry human faces and mildly shocked after viewing 1 face, but not the other. Then the task was reversed, with the aim of having the participants “unlearn” their original fear conditioning and testing their ability to relearn how to respond to negative surprises in the environment.
Although all participants were able to perform the reversal learning, the researchers found “pronounced differences in the ‘learning rates.’” Highly symptomatic veterans tended to overreact when what they expected to happen and what actually happened did not match up.
The researchers say they found biomarkers that could explain the different reactions. In the highly symptomatic veterans, 2 areas of the brain—the amygdala and striatum—were less able to track changes in threat level.
“One’s inability to adequately adjust expectations for potentially aversive outcomes has potential clinical relevance,” said Ilan Harpaz-Rotem, PhD, co-leader of the study, “as this deficit may lead to avoidance and depressive behavior.”
The researchers say their findings could give a “more fine-grained understanding of how learning processes may go awry in the aftermath of combat trauma.”