In a Perspective article published in the journal Neuron, two professors at the University of Michigan (U-M) Medical School present a new theory of post-traumatic stress disorder (PTSD), suggesting that an inability to perceive the true context of the moment may play a major role in the disorder.
The researchers believe the new theory helps unify current separate models of PTSD. They also hope to stimulate interest in the theory and invite others in the field to test it.
In the article, the experts explain that people with PTSD appear to suffer from disrupted context processing, a core brain function that allows us to recognize that a particular stimulus may require different responses depending on the context in which it is encountered. Knowing the right context allows us to call upon the “right” emotional or physical response to the current encounter.
For example, a mountain lion seen in the zoo would not warrant a “fight or flight” response, while the same lion unexpectedly encountered in your backyard most likely would.
For a person with PTSD, a stimulus associated with the trauma they previously experienced — such as a loud noise or a particular smell — triggers a fear response even when the context is very safe. So the benign sound of the front door slamming or the smell of food burning on the stove may elicit the same fear response as a previously terrifying situation.
Context processing involves a brain region called the hippocampus, and its connections to the prefrontal cortex and the amygdala. Research has shown that activity in these brain areas is disrupted in PTSD patients.
The researchers hope their theory can unify wide-ranging evidence by showing how a disruption in this circuit can interfere with context processing and can explain most of the symptoms and much of the biology of PTSD.
“We hope to put some order to all the information that’s been gathered about PTSD from studies of human patients, and of animal models of the condition,” said Israel Liberzon, M.D., a professor of psychiatry at U-M and a researcher at the VA Ann Arbor Healthcare System who also treats veterans with PTSD.
“We hope to create a testable hypothesis, which isn’t as common in mental health research as it should be. If this hypothesis proves true, maybe we can unravel some of the underlying pathophysiological processes, and offer better treatments.”
One particular problem, say the researchers, is that none of the current PTSD models can sufficiently explain the various symptoms nor all of the complex neurobiological changes seen in the disorder.
For example, the first model of PTSD is based on abnormal fear learning. It is rooted in the amygdala, the brain’s “fight or flight” center that focuses on response to threats or safe environments. This model emerged from work on fear conditioning, fear extinction and fear generalization.
The second model, exaggerated threat detection, is rooted in the brain regions that figure out what signals from the environment are “salient,” or worth paying attention to. This model focuses on vigilance and disproportionate responses to perceived threats.
The third model, involving executive function and regulation of emotions, is mostly based in the prefrontal cortex, the brain’s center for keeping emotions in check and planning or switching between tasks.
By focusing only on the evidence bolstering one of these theories, researchers may be “searching under the streetlight,” said Liberzon. “But if we look at all of it in the light of context processing disruption, we can explain why different teams have seen different things. They’re not mutually exclusive.”
The main thing, says Liberzon, is that “context is not only information about your surroundings — it’s pulling out the correct emotion and memories for the context you are in.”
A deficit in context processing would lead PTSD patients to feel “unmoored” from the world around them, unable to shape their responses to fit their current contexts. Instead, their brains would impose an “internalized context” — one that always expects danger — on every situation.
The researchers say this type of deficit, developing in the brain as a result of both genetics and life experiences, may create vulnerability to PTSD in the first place. After trauma, a vulnerable person might develop symptoms of hypervigilance, sleeplessness, intrusive thoughts and dreams, and inappropriate emotional and physical outbursts.