Century-old Experiment Helps Researchers Understand PTSD

Century-old Experiment Helps Researchers Understand PTSD

Posted by Dr. Michael Roy, Professor of Medicine at Uniformed Services University of the Health Sciences on February 20, 2014

Illustration of a three-dimensional side view of the brain
This illustration shows a three-dimensional side view of the brain. The amygdala lies deep within the brain and the brain stem. (Photo courtesy of National Institutes of Health)

Why do posttraumatic stress disorder (PTSD) symptoms persist in some people and not others? An experiment performed more than 100 years ago is helping us find answers.

Our team and researchers at other top universities are learning more about PTSD using Russian scientist Ivan Pavlov’s famous “conditioned response” experiment. Working with service members with and without PTSD, we hope to better understand the disorder to improve diagnosis and treatment.

The experiment

One experiment, based on Pavlov’s discovery, involves observing how someone with PTSD experiences fear. The feeling of fear is an important cue to deciding if our surroundings are safe or dangerous. It also prepares us to respond. A part of the brain known as the amygdala plays a big role in deciding whether to stay where we are or run away, the “fight or flight” response.

In this experiment, we show individuals colored shapes on a computer screen. One pattern of shapes is paired with an uncomfortable puff of air directed to their throats. We show the shapes and then measure their physiological responses, such as heart rate, blood pressure, sweating and eye blinking. Their responses indirectly measure how their brain responds to stimuli. The amygdala and other parts of the brain trigger those responses.


During the experiment, study participants learn that one pattern of shapes signifies danger with the puff of air, while another pattern signifies safety, or no puff of air. Participants with PTSD tend to have a greater physiologic response to the danger cues — increased heart rate, blood pressure, sweat response and eye blinking, than those who don’t have PTSD. This holds true even if they’ve had similar traumatic experiences, such as combat.

After study participants have learned whether danger is near or not by the pattern of shapes they see, they’re shown the shape that means danger together with the one that means safety. Those with PTSD tend to pay more attention to the danger signal. Those who don’t have PTSD focus on the safety signal. We know this by their physiological responses.

What we learned

From this experiment we learned that individuals with PTSD find it harder to control their fear response even when danger and safety signals are present at the same time. The danger cue promotes such a fear of something bad happening that they can’t believe in the safety cue. This pattern fits with studies of the brain that show that the frontal lobes, which normally control the fear centers of the brain, don’t perform as well in individuals with PTSD.

To learn more about the relationship between PTSD and the brain, we look at how the brain functions in the same patients who did the shapes experiment. For this we use a special tool called functional MRI. The tool measures changes in oxygen levels in different parts of the brain. That gives us certain types of information, such as how strongly the amygdala responds to fear.

New imaging techniques, technologies such as virtual reality, and mobile applications such as smartphone apps can help us understand and treat PTSD. Come back to the DCoE Blog to hear more about what we’re learning from these remarkable tools in future articles.

Retired Army Col. (Dr.) Michael Roy is a professor of medicine and director of the Division of Military Internal Medicine at Uniformed Services University (USU), and director of recruitment for USU’s Center for Neuroscience and Regenerative Medicine. He’s the principal investigator on multiple studies about war-related health that often use cutting edge technologies and virtual reality therapy.