The Neuroscience of Fear Responses and Post-Traumatic Stress

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Two recent studies offer new clues about how the brain copes with traumatic events that can trigger flashbacks and lead to post-traumatic stress disorder (PTSD). Do you suffer from some form of PTSD? I do. Hopefully, these new findings will lead to more effective treatments and interventions that will combat the debilitating power of PTSD.

The statistics on post-traumatic stress are alarming. In the general population, it's estimated that about 7 or 8 out of every 100 people will experience PTSD at some point in their lifetime. About 8 million American adults are clinically diagnosed with PTSD during any given year. Approximately 10% of women in the general population develop PTSD at some point in their lives, compared to about 4% of men.

The statistics for veterans suffering from PTSD are much higher. According to the U.S. Department of Veterans Affairs, it’s estimated that about 30% of Vietnam Veterans suffer from PTSD. As many as 20% of those who served in Operations Iraqi Freedom (OIF) and Enduring Freedom (OEF) have been diagnosed with PTSD. About 12% of Gulf War Veterans have been diagnosed with PTSD.

What Triggers Symptoms of Post-Traumatic Stress Disorder?

In a recent study, researchers in North Carolina identified that certain brain regions function atypically in people with PTSD. These changes in brain function make someone with PTSD more vulnerable to generalized anxiety that can be triggered by any stimuli that vaguely resembles the original fear conditioning. According to the researchers from Duke Medicine and the Durham VA Medical Center, these findings suggest that exposure-based PTSD treatment strategies might be improved by focusing on “tangential triggers” to the initial event.

The December 2015 study, “Fear Learning Circuitry Is Biased Toward Generalization of Fear Associations in Posttraumatic Stress Disorder,” was published in the journal Translational Psychiatry.

For this study, the scientists enrolled 67 military veterans who had been deployed to conflict zones in Iraq or Afghanistan after Sept. 11, 2001, and who had been involved in traumatic events. About half of the study participants had been diagnosed with PTSD.

All of the participants were placed in an fMRI and shown a series of five facial images that depicted a spectrum of emotions that ranged from neutral, to moderately scared, to terrified. The initial brain scans didn’t identify any differences between those with and without PTSD.

Then, the participants were taken out of the fMRI and shown the same images again while being given a mild electrical shock while viewing the middle image of a face only showing moderate fear. After this fear conditioning associated with the middle image, the patients underwent another fMRI scan as they viewed all five faces again.

Interestingly, those with PTSD had heightened brain activity when they saw the most fearful face and associated it with the electric shock, even though they had actually experienced shocks while viewing the middle image that was only moderately fearful. The non-PTSD group of participants correctly associated the middle face with the electrical shock and had heightened brain activity only when viewing this image.

Patients with PTSD often show differences in fear acquisition and extinction relative to trauma victims without PTSD. However, the researchers believe that symptom triggers may only vaguely resemble the index trauma and may differ from the trauma experience in "shape, context, emotional valence, smell, semantic association, and other dimensions."

In a press release, Rajendra A. Morey, M.D., an associate professor in the Department of Psychiatry and Behavioral Sciences at Duke and director of the Neuroimaging Lab at the Durham VA Medical Center said,

"We know that PTSD patients tend to generalize their fear in response to cues that merely resemble the feared object but are still distinct from it. This generalization process leads to a proliferation of symptoms over time as patients generalize to a variety of new triggers.

Our research maps this in the brain, identifying the regions of the brain involved with these behavioral changes. The PTSD patients remembered incorrectly and generalized their anxiety to the image showing the most fearful expression. This phenomenon was captured in MRI scans, showing where the PTSD group had heightened activity.

The amygdala, which is an important region in responding to threat, did not show a bias in activation to any particular face. But there was a definite bias of heightened activity in response to the most frightened expression in brain regions such as the fusiform gyrus, insula, primary visual cortex, locus coeruleus and thalamus."

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The researchers believe the visual cortex is significant in PTSD because it's not only doing visual processing, but also assesses potential threats. The locus coeruleus is also important because it's responsible for triggering the release of adrenaline during stress or serious threat during "fight or flight" responses.

This breakthrough discovery on functional brain differences in those with PTSD provides a neurobiological model for assessing fear generalization in which PTSD symptoms are triggered by things that merely resemble the source of original trauma.

"People with post-traumatic stress disorder grow anxious based on reminders of past trauma, and generalize that fear to a variety of triggers that resemble the initial trauma," Morey concluded. "Current fear conditioning therapies are limited by repeated use of the same cue to trigger the initial trauma, but they might be enhanced by including cues that resemble, but are not identical to, cues in the original trauma."

Double Whammy: A Second Unpredictable Traumatic Event Increases PTSD Risk

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My personal experiences with fear-conditioning and PTSD all occurred a few blocks from my apartment in the East Village of Manhattan. I had two traumatic events happen near my apartment within a few weeks of one another. These events permanently encoded this part of my neighborhood as being a dangerous place—even though, in reality, it is an extremely safe neighborhood.

In the summer of 2003, I was casually walking home from dinner at Pete's Tavern, when I was attacked by three guys in Stuyvesant Park at 16th Street next to Beth Israel Hospital. The assailants hit me on the back of the head with some type of object and then kicked my skull repeatedly as I was curled up helplessly in the fetal position bleeding onto a slab of concrete next to the fountain. Although I got over that trauma, a few weeks later, I was walking along 16th Street, when out-of-the-blue, a huge planter fell off a fire escape and smashed on top of a stranger’s head who was walking a few paces ahead of me.

Again, there was blood all over the concrete and I had instantaneous flashbacks to being beaten up a few weeks earlier. The guy who got hit by the planter was knocked out, totally unconscious, and bleeding from his head onto the sidewalk. I waited for the ambulance to arrive, but I don't know if he lived or died. The whole event happened in slow motion, and again, I saw my own life flash before my eyes. If I'd been walking two seconds faster, the planter would have fallen on my head... Based on the second unpredicted experience of seeing someone suffer traumatic head injuries, I became superstitious and spooked by this vicinity of New York City. To this day, I consciously avoid walking on East 16th Street.

I was reminded of my own fear-conditioning after reading another recent study on PTSD by researchers at New York University (NYU) who found that a singular traumatic experience is enough to rattle someone, but rarely takes them down. However, the researchers found that a second subsequent trauma that is unpredictably linked to the first can be the ‘straw that breaks the camel's back’ and results in post-traumatic stress disorder.

The December 2015 study, “From Memory Impairment to Posttraumatic Stress Disorder-Like Phenotypes: The Critical Role of an Unpredictable Second Traumatic Experience,” was published in the Journal of Neuroscience.

For this experiment, the scientists placed rats in a box that was brightly lit on one side and dark on the other side. In general, rats like to avoid brightly lit areas. Predictably, the rats headed into the dark side of their habitat. Upon entering the shaded side, the rats were given a mild electrical shock to their feet. Then, the researchers scooped them up and returned them to their home habitats where they were never shocked.

Later, the researchers measured how well each rat remembered the shock they’d experienced by having the animals revisit the electrified enclosure while measuring how long they stayed in the lighted area before retreating to the dark side, where they'd been shocked once before. After just a single shock, the fear-conditioning hadn't been hardwired, and the rats quickly ventured back into the dimly lit areas. However, after a second experience of being shocked with higher voltage in the dark area, the rats began to display fear and anxiety and avoided the area. This is classic “Skinner Box” fear-conditioning in action.

However, what really pushed the rats over the edge, was being administered random and unpredictable electrical shocks anywhere in their cage. The second shock actually came in two forms: sometimes quite predictably in the same dark corner of the cage, but sometimes in a completely lighted environment where the rats could not predict it.

When the shock was unpredictable, the researches were able to identify that it pushed the rats into showing symptoms that echo PTSD in humans. In a press release, co-author Cristina Alberini, a neuroscientist at New York University, said,

"Our conclusion was that two traumatic experiences are actually critical for the development of these symptoms. Although a first traumatic experience elicits a blunted stress and memory expression, perhaps as protective measure, an unpredictable second traumatic experience, therefore multiple traumatic hits, critically contributes to generating behavioral responses typical of PTSD.

The good news is that now we have a model [in rats] in which we can study this post-traumatic condition and hopefully test for treatments that may alleviate these problems.”

Conclusion: More Research Is Needed to Identify Effective PTSD Treatments

Hopefully, these new findings will lead to more effective interventions to help people with PTSD overcome paralyzing fear-conditioning—but more research is needed. If you'd like to read more on possible ways to overcome fear responses, check out a free sample of my chapter on behavioral conditioning and avoidance learning in The Athlete's Way.

To learn more about PTSD check out my previous Psychology Today blog posts:

• "The Neuroscience of Post-Traumatic Stress Disorder"
• "The Cerebellum May Be the Root of PTSD in Combat Veterans"
• "Two New PTSD Treatments Offer Hope for Veterans"
• "Surf Therapy and Being in the Ocean Can Alleviate PTSD"
• "Cortisol and Oxytocin Hardwire Fear-Based Memories"
• "How Does the Vagus Nerve Convey Gut Instincts to the Brain?"
• "The Neurobiology of Grace Under Pressure"
• "Chronic Stress Can Damage Brain Structure and Connectivity"
• "Neuroscientists Identify the Roots of 'Fear-Evoked Freezing'"
• "Decoding the Neuroscience of Fear and Fearlessness"
• "Optogenetics Allow Neuroscientists to Turn Fear Off and On"
• "Our Amygdala Influences Kindness and Altruism, Not Just Fear"
• "5 Neuroscience-Based Ways to Clear Your Mind"

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