Research shows that observing other's stresses can change connectivity in the brain.
Post-traumatic stress disorder (PTSD) develops in some people following a frightening, dangerous, or shocking event.
Although most people do not develop PTSD after such an experience, an estimated 7-8 percent of people in the United States will experience PTSD during their life.
Symptoms vary from individual to individual, but can include flashbacks, intrusive negative thoughts, avoiding places, events, or objects, and being easily startled.
Even if a specific event does not trigger PTSD at the time, it raises the chance of an individual developing it at a later date.
PTSD without experiencing stress
PTSD can be a life-altering condition. However, the trauma is not limited to the individual who lived through the traumatic event; it can touch anyone who interacts with this person. This can include caregivers, loved ones, or anyone who witnesses or hears about the others' suffering.
Lead author of the current study, Alexei Morozov - an assistant professor at the Virginia Tech Carilion - says:
"There's evidence that children who watched media coverage of the September 11 terrorist attacks are more likely to develop PTSD later in life when subjected to another adverse event."
In 2008, RAND Corp. - a nonprofit group that helps guide policy through research and analysis - assessed a number of studies on PTSD in previously deployed service members. They found that people who had not experienced a serious incident but had heard about it were just as likely to develop PTSD as those who had been involved in it. This is referred to as observational fear.
In earlier studies, Morozov and Wataru Ito - a research assistant professor at the Virginia Tech Carilion Research Institute - investigated observational fear in a rodent model. They found that animals that witnessed stress in others, without experiencing any negative events themselves, displayed an increased fear response in other situations.
Following on from these findings, the team set out to investigate any neurological changes that might underpin the observed behavioral changes.
Specifically, they researched the prefrontal cortex, which is an area of the brain involved in understanding the mental state of others and empathy. Their results are published in this month's Neuropsychopharmacology.
Brain changes in PTSD mouse model
Researcher Lei Liu measured neural responses in the brains of mice who had witnessed a stressful event in another mouse. The experiment involved placing two mice in adjoining cages. The cages were separated by a Plexiglass wall with holes large enough to be able to hear and smell their neighbor and touch whiskers.
One of the mice (the demonstrator) received 24 electric shocks through the floor of the cage, one every 10 seconds. The other mouse (the observer) did not receive shocks. The next day, the brain of the observer mouse was examined for changes.
Specifically, the team charted signal transmission through the inhibitory synapses that moderate the strength of signals being shipped to the prefrontal cortex from other brain areas.
"Liu's measures suggest that observational fear physically redistributes the flow of information. And this redistribution is achieved by stress, not just observed, but communicated through social cues, such as body language, sound, and smell."
The changes measured by the team indicate that communication is increased via synapses in the deeper layers of the cerebral cortex, but less so in more superficial layers. This study demonstrates that while changes certainly occur, it is not clear at this stage what the exact changes are.
As Morozov says: "Once we understand the mechanism of this change in the brain in the person who has these experiences, we could potentially know how something like post-traumatic stress disorder is caused."
Although these findings can be considered preliminary, the hope is that the more we know about the changes, the more we will be able to understand how best to treat PTSD.