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Century-old Experiment Helps Researchers Understand PTSD

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.

Comments (36)

  • Christina 24 Feb

    This was enlightening. Ty
  • Hal 25 Feb

    Hi, I am a "Recovered" PTSD Viet Nam "Survivor". The "Fight or Flight" responses are basically under control, although I still have a noticeably ' short fuse' about some things. My recovery can be almost solely contributed to Love. Went thru a 'program' at Jackson VAMC.............. it was kind of experimental, in 1983/84. It was bascially useless and cause me to loose most everything that meant anything to me(Girlfriend/fiance, son, career etc etc). My salvation came from getting away from Jackson and all of the then current VA treatments and falling back onto internal strength of character and getting back the woman that I loved. My biological family was a big help(dad was a WWII combat vet, mom a WWII nurse). All of that LOVE pulled me off the brink and got me to put all in perspective. You can do all the studies you want, But Family Support/Understanding are THE Single most important thing to get you thru it. It also helps to be able to talk with other Survivors and learn from them different experience's as survivor's. Just thought I would pass this along. Maybe something in here is useful for you. The men coming back now have it Much Worse then Any Generation of American Soldiers.......Ever.
  • DCoE Public Affairs 26 Feb

    @Christina, Glad you liked it and thanks for sharing. 
  • DCoE Public Affairs 26 Feb

    @Hal, We agree that the support and involvement of family can play a crucial role in helping someone who is experiencing physical or psychological wounds. We're glad your family was a huge help in your recovery. Thanks for sharing and for your service.

  • Gerald Holloway 03 Mar

    I am happy that you have had your PTSD cured and do not have to experience it anymore.  I to have PTSD but even with the same or similar support from my family I still suffer with PTSD.  I still cannot say I am cured from PTSD.  I am still confused by what you say to be a fact.  Good luck to you and I am happy you beat it.  Semper Fi!
  • John B. Jordin 03 Mar

    To me PTSD doesn’t have anything to do with controlling my fear. It has to do with controlling my emotional responses. I cry at things that I would never had cried at before. My temper flares up at things that it shouldn’t flare up at. Maybe I don’t have PTSD if you have to have a fear element. Mine is all emotional control. I have been diagnosed as PTSD by the Atlanta VAMC.
  • John 03 Mar

    This is well known for many years. In one of the classes at VA, I had the teacher go into depth explaining it to the class . You should have seen the reaction of these vets. To get a real answer was overwhelming comforting to these vets. Why the VA does not spend time retraining that gland into positive wellness is puzzling to me. No doctor has ever explained to me or any other vet. Very upsetting to me that these vets have not been given a reason for their PTSD. I applaud this writer for writing this story.
    the other thing that puzzles me is these brain injuries exclusive to Iran and Iraq veterans. In Vietnam- nam, mortar explosions and artillery and other explosions have rattled brains in soldiers from world war 1, 2, Vietnam-nam etc. Treat and test these people too. It amazes me the logic of the VA.
  • Dan 03 Mar

    I have ptsd and suffer with terrible headaches. I wake up scared with headaches. Any thoughts?
  • Gil Jones 03 Mar

    I've had PTSD since Vietnam 67.  After two VA and two private programs I thought I'd never get relief.  In 73 I stumbled upon Scientology and got relief.  Their remedy had nothing to do with the brain, had everything to do with mental image pictures/memories and their ability to 'drain' the charge connected to those memories...Semper Fi Nam 66-67
  • william ebrecht 04 Mar

    It will be interesting to see if there is a difference between Viet Nam vets who have had PTSD for possibly 40 years: and more recent vets who have access to treatment much sooner.  Will a measurable difference be found in the persistence of symptoms in those with longer or shorter term disorders.
  • xmilmt 04 Mar

      It's great that there are some of you that have family to support you, my father was a WWII vet but he almost never talked about it and he's gone now. I am a 29 year vet retired in 2004 and got to all the crap that went on. Did the anger management program and ended up on a permanent pill regiment for it and the headaches, and nightmares. But that's not the worst, the problem is people are not  Pavlov’s famous dog and the “conditioned response”  experiment. The worst is not reacting or feeling anything or caring about anything and just going thru the motions of having a happy life when it just doesn't matter anymore. So what do you phd's do for the 10% of the old soldiers that are too far gone for the VA to spend the time or money on and just give us another pill to try. And here it is midnight and the migraine is killing me so sleep is out guess I'll just vent.

    Be safe and be proud because you are the Greatest Generation of American Soldiers EVER! XMILMT

  • Dennis 04 Mar

    I'm a Vietnam veteran who has had problems with PTSD since around 1981. Got SC in 1986 and I'm now 100%. I've lived with symptoms since the war. At first, I thought it was my normal behavior and I was the only one like that. The Marine Corps taught me to survive in war, and once I survived war, that intense feeling never goes away. I will give myself the best chance to survive in any situation. That's why if you put a safety zone next to a danger zone, I will always react to the danger zone because as long as it exists, the safety zone is never really safe. Someone has to be on guard and be able to react. That's what Marines do. I turn emotionally stone cold as ice when threatened with attack. I never fear the threat. I just want to end it. I believe that aspect of my personality is learned behavior, the same as symptoms of PTSD are learned behavior. They become part of you and can't be removed.
  • Peter G DeRosa, MD 04 Mar

    I enjoyed reading your updated application of old information. As a practicing psychiatrist and following my active duty with the USAF, back in the 70's, I was actually training patients who manifested symptoms of excessive levels of arousal, to modify those levels through control of sympathetic activity by the cognitive raising of their finger temperature. This activity appeared to generalize the reduction of sympathetic nervous system activity beyond the specific target of increasing digital temperature. This was a successful tool used in my private practice, with civilian patients, and diminished the need for medication. 
  • J D 04 Mar

    I what to let you know that I survived the V N era and the first Gulf war but there is an ever lasting picture in my head and I am trying still to day to bare the dreams and the flash backs that takes place each and every day in my life.
    I forget where I am a lot of times and I keep seeing the children and my buddies be hurt or killed when I could not help them. and if it wasn't for the pastors I meet with every two weeks helping me and most of all, our Lord Jesus Christ is always here with me to comfort me and to put my mind at a some what different place away from the wars and killings and helps me to keep my eyes on him. I am better than I was a few years ago. So I think if we get with a Christian group to help us it will make things a little easier. May Jesus Bless you all that are in need of help.
  • DCoE Public Affairs 04 Mar

    @Dan, If you’re interested in information on the possible association of PTSD and headaches, please call the DCoE Outreach Center at 866-966-1020, email or live chat with someone at The center is available 24/7 and can assist you in finding information and resources on this topic.


    I was diagnosed with PTSD by a psychiatrist at Tampa, VA in Jan 2013. Prior to that I had open heart surgery with 5 by-passes in 2008 due to prior heart attack while on active duty in 1988.  Shortly after, I started having seizure like episodes at night while sleeping.  I started yelling, screaming and shaking in my sleep.  It scared my wife so I went to the VA in Buffalo it appeared that I had epilepsy, seizures and they prescribed seizure medications which I still am taking.  The psychiatrist in Tampa prescribed fluoxetine 10mg, and galantamine hyd 8mg for my memory loss, but my memory continues to fade and I am only 65.  I have not had any seizure or sleeping disorders for over a year because of the fluoxetine does in fact work it removes all  the depression I was also having.  But my memory is going downhill, my hands shake when I hold something and my leg starts to almost move like a drummers when I am on the computer or doing a Sudoku  puzzle or just thinking about something.  Is it possible that the medications prescribed for seizure episodes was incorrect and has hurt my memory and compounded this PTSD?   I was at Dong Tam in the Mekong Delta with the Navy Seabee's, we were under constant mortar fire during 1969.  Who could ever believe that this comes out after 40 years???  Not much was said about this PTSD stuff back in 2008, I guess that's why I was mis-diagnosed.   I have tried, twice to get my disability increased with the VA in 2008 and again in 2011 it has been hard and taken quite a while with rejections because seizure disorders were not a cause of active duty??? I've just re-applied last year with this PTSD diagnosis.  You think I have a case???? How long before an approval?  I guess it did happen while on active duty after all...
  • phil t 04 Mar

    I am combat vet of Vietnam. I participated in 7 various ptsd treatment programs. I also returned to Vietnam 2 times in the 2000 and 2005. To share experiences and trauma with other vets was temporarily helpful. However my hyper-vigilance never altered. My conscious mind has no fear of war memories or enemy combatants. My sub-conscious mind is ever on alert and I continue to have nightmares on a nightly basis. Not sure if any vets have found relief from like symptoms. I have heard of  therapy that claims these sub-conscious triggers can be eradicated. Any info would be helpful
  • Richard C. Crepeau 04 Mar

    I am hoping that this gets through. My earlier comments seem to disappear.
    I am a second generation Warrior, my dad was a career USAF Officer, and fought as a B-24 pilot in WWII and as an intelligent officer in Vietnam while I was in the Marines in I Corps 1966-67. I went undiagnosed with PTSD until 1996, plagued with the various symptoms described above. I then was introduced to a superb CBT psychologist who for 6 yrs. allowed me to receive her counseling and training.
    I was able to read then and finish 200+/- books on the history of PTSD and psychology in general. When she retired I did also from the VA assistance. I thought I had 'beaten' something but since PTSD is unbeatable I assumed I hadn't. Then four years later I was ordered to return and met superb recreational/CBT psych. who then helped me resolve work, marriage and future retirement issues for three yrs after he retired. I then became infected with a faciitusstaph disease which cost me my left foot, damage to my rt. wrist, knee damage and comatose for a month in 2010. I since then have been recovering for the third time from PTSD with a combination of the 'new' neuroplasticity of the brain, meditation/ mindfulness, physical training and positive psychology from Dr. Seligman, and six-ten other Positive Psych's including Dr. Tedeschi and Calhoun. I now intend to buy a Dragon and tame it and write notes on how to repeat my sofar success w/o hurting other Vets from getting maximum assistance. My Dad died from undiagnosed PTSD and alcohol and survival quilt. I don't want then new and next twenty years of war Vets to continue to see a hopeless world of lifetime crippling PTSD.
    Sincerely, SF, Richard Crepeau USMC
  • Roland Hiles 04 Mar

    I am a ww2 vet and still have haunting memories of my time in Normandy. While fighting in France in the hedgerows I charged a machine gun nest killing three German soldiers and received the Bronze Star for this deed. But as June rolls around each year I still relive that time that I had sent three men into eternity.I still have a feeling of guilt wondering how the parents or if they were married and had children  how they wondered how they had died. But life goes on.
  • Paul K. 05 Mar

    Interesting article.  I just wanted to point out that having PTSD does not always have to be combat related.  Many of us served in zones where combat was not present , but terrorist groups were present that hated U.S. military personal and took the lives and wounded many of them.  They are under reported and go down in history as ghosts.  When you go to work everyday in the military, you are willing to die for millions of free Americans that you do not even know.  The threat of having people who want to kill you weighs heavy on the brain.  There is no simple solution to PTSD, but remember that we are special and only 1 % of the U.S. population.  To all who suffer with a military disability, I say, thank you for your willingness to die for me so that I and millions of other Americans can live free.  Thanks to all who served!!!!
  • DCoE Public Affairs 07 Mar

    @Phil, First off, thank you for your service. Secondly, we definitely want to try to get you some information on this. Please call the DCoE Outreach Center at 866-966-1020 or email The center is available 24/7 and can assist you in finding information and resources on psychological health concerns.

  • Bob Deschner, Vet TRIIP, Inc. 08 Mar

    I commend you on your elegant experiment. It is interesting that the uncomfortable puff of air was directed to the throat. It would be interesting to see whether the side of the throat mattered (left or right). Dr. Eugene Lipov's work with stellate ganglia blocks (C6 right side to block descending vagus nerve) would suggest an asymmetric response.

    I noticed that you conclude that the frontal lobes don't perform as well in individuals with PTSD. I suggest that it is more likely that the amygdala response is stronger than normal (more highly conditioned--even with one event learning) with those with PTSD--something similar to the kindling process that happens during and after severe seizures.

    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.

    Keep up the great work.
  • Nichole 09 Mar

    I am preparing to write an article to be published at my university. I have done a recent survey involving PTSD. If anyone has information or would like to take my survey, please send me an email. I am very excited in doing more research on the topic of PTSD since I am a veteran.
  • Dr. Roy 17 Mar

    @Dan, Headaches are very common and there can be a lot of different reasons for them. Among the reasons is not getting quality sleep, which the nightmares of PTSD can certainly interfere with. TBIs can also cause headaches, and CNRM ( has a variety of studies that could assess you for this and see if there is something that might be able to help you.

  • Dr. Roy 17 Mar

    @William, In general, the sooner the treatment, the easier it is to treat. When symptoms have been present for decades it is usually going to be harder to get them to resolve.

  • Dr. Roy 17 Mar

    @xmilmt, Thank you for your service. We are definitely not implying that people are dogs. The fact that there are some similarities in responses only means that these pathways in the brain are very important since they have been preserved across species throughout evolution.

  • Dr. Roy 17 Mar

    @Dennis, I think your description is very accurate, and is exactly what we see as well. The responses that you learned clearly served you very well and helped to keep you alive, and that is of inestimable value. However, if the same response makes it difficult to relate to others and enjoy life, if we can help you do such things better we and other medical providers certainly want to try to do so.

  • Dr. Roy 17 Mar

    @Peter, This is very interesting, and it sounds like you were way ahead of your time with a biofeedback method. Thank you for sharing this.

  • Dr. Roy 17 Mar

    @JD, What you describe is very common, and we are glad to hear you have improved some. Please don’t hesitate to reach out to others as well for help if needed.

  • Dr. Roy 17 Mar

    @Paul, You are completely correct, PTSD can occur from a wide variety of traumatic experiences, not just combat. One new study we are about to start is intended to help those who do not have full PTSD, but just some symptoms, using smartphone apps. And it does not just help those after combat, but also those who may have witnessed mass shootings, bombings, or even natural disasters like hurricanes and earthquakes. We have also found that many with PTSD after combat have also had other life traumas in addition.

  • Dr. Roy 17 Mar

    @Roland, It is very common for those who have had such an experience to remember, and have more symptoms, around the anniversary of an event, and survivor guilt is a particularly common one. A sincere thanks for your service.

  • Dr. Roy 17 Mar

    @Richard, I am sorry to hear that you have had such difficult experiences, but it sounds like you are quite resilient as well, and have gotten some good help along the way. The positive attitude and “fight” that comes across in your message is as important, if not more so, than anything anyone else could ever do for you though.
  • Dr. Roy 17 Mar

    @Phil, That is a good question. We are still learning more about what causes certain types of symptoms to persist, and hopefully as we learn more we will be better able to treat such persistent symptoms.  I think meditation, yoga, or other relaxation techniques might be particularly helpful with hypervigilance symptoms, but suspect you may have already tried some of these?

  • Dr. Roy 17 Mar

    @Joe, Symptoms can become more apparent at any time in your life, as you have discovered. There are likely a lot of reasons that contribute to them coming out at different times. For example, the severity of your heart condition might have led you to think about your life being in danger, which in turn caused you to reflect on when it was before, or just to review your life history more. I can’t really tell you what the disability system might do, but I do encourage you to try to get some help for your symptoms so that you can have the best quality of life now.

  • Jessica 26 Dec

    I came across this article while I was stalking my sister's Facebook page. My father was an alcoholic and as a result, I have struggled w PTSD since childhood (I am now almost 36). This article was really easy to understand, even as a civilian w a high school education. I also found that it made a lot of sense, and I actually had a lightbulb go off at one point when it said "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." It helped me to understand WHY I still have triggers, even if I am in a safe environment. I just wanted to say thank you for this really informative article, and I will be following your page for more studies and articles in the future.
  • DCoE Public Affairs 19 Jan

    Thanks, Jessica. We're so glad you found this blog post and that it was helpful! We look forward to you following our blog. 

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