![Illustration of brain regions studied in mental illness: ACC, amygdala, hippocampus, prefrontal cortex. [NIH]](https://sp-ao.shortpixel.ai/client/to_webp,q_glossy,ret_img,w_750,h_375/https://www.psypost.org/wp-content/uploads/2015/08/Hippocampus-prefrontal-cortex-amygdala-anterior-cingulate-cortex-by-NIMH-750x375.jpg)
A new neuroimaging study showed that people suffering from posttraumatic stress disorder (PTSD) exhibited increased activation in the amygdala region of the brain when shown surprised and neutral facial expressions. The same phenomenon was observed in identical twins of these individuals who did not suffer from PTSD.
The study, which was published in the Journal of Psychiatric Research, sheds new light on the neural mechanisms underlying the development of PTSD.
PTSD is a condition that develops in approximately 20% of individuals exposed to psychological trauma in their lifetime. It is defined by wide clusters of symptoms that include intrusive memories, negative alterations in mood, heightened levels of arousal, and other symptoms. Currently, there are many treatment options available for PTSD; however, for some patients, the treatments offered do not provide clinical relief.
“There are many symptoms that define PTSD, and one of them is hypervigilance, or always feeling the need to monitor the environment for potential threats,” explained study authors Cecilia A. Hinojosa and Lisa M. Shin, a postdoctoral research fellow at Emory University and a psychology professor at Tufts University, respectively.
“Previous research suggests that hypervigilance may lead us to respond even to signals that are ambiguous and not clearly threatening. Thus, we were interested in this topic to learn whether individuals with PTSD showed differential brain activation to ambiguous signals of threat compared to individuals without the disorder.”
“We were also interested in uncovering the origins of abnormal brain activation found in individuals with PTSD to determine whether such abnormalities may make an individual more vulnerable to developing the disorder after experiencing trauma or whether these abnormalities are acquired characteristics of the disorder,” the researchers said.
“Determining whether these abnormalities are vulnerability markers may allow us to create early interventions designed to prevent the development of PTSD. Alternatively, if these brain abnormalities represent acquired characteristics of the disorder, we may be able to use them to help with diagnosis and/or with assessing response to treatment.”
Functional neuroimaging studies of patients with PTSD have revealed exaggerated activation in the amygdala region of the brain in response to stimuli related to threat and trauma. The magnitude of these responses was higher in patients with more severe symptoms of posttraumatic stress disorder.
Studies have also shown decreased activation of the medial prefrontal cortex region of the brain in response to fearful facial expressions, to stimuli that remind the person of the trauma they experienced, and at rest.
It was, however, unclear whether such activation anomalies also occur in response to more ambiguous stimuli. The researchers hypothesized that this might indeed be the case and that hypervigilance symptoms of PTSD might be associated with a tendency to interpret ambiguous and neutral stimuli as threatening.
To study this issue, the researchers conducted a neuroimaging study using functional magnetic imaging (fMRI) of four groups of participants – 12 participants who experienced psychological trauma and had PTSD along with their identical twins who did not experience trauma and 15 participants who experienced psychological trauma but did not have PTSD along with their identical twins who did not experience trauma.
The participants completed assessments of childhood trauma, depression, anxiety, and were screened for alcohol use disorder. The combat exposure severity index was calculated for participants who were exposed to combat in their life.
Participants then underwent brain scans during which they were presented grey-scale images of faces organized into four blocks showing surprised facial expressions and four blocks showing neutral expressions. Images used showed four male and four female models displaying surprised and neutral facial expressions, for a total of 16 unique images. Within each block, participants were shown 32 images, each very briefly, for 200 milliseconds with a 300-millisecond interval between two images, organized so that no model was presented twice in a row.
After the neuroimaging session, participants completed a questionnaire in which they were shown all the images again and asked to write down the emotion displayed by each image. They also underwent a session where each of the 16 images was presented to them for 3 seconds and they were asked to rate the valence and arousal qualities of that facial expression i.e., whether the expression displayed a positive or a negative emotion and how intensive that emotion was.
The researchers found that participants with PTSD and their identical twins (with no trauma exposure or PTSD) both exhibited greater activation in the amygdala regions compared to participants without PTSD and their identical twins while they were shown images with surprised facial expressions. Participants who had PTSD exhibited lesser activation than the other three groups in the medial frontal gyrus region of the brain.
Both participants with PTSD and their identical twins exhibited greater activation in the right amygdala region of the brain compared to the other two groups of participants when shown images with neutral facial expressions.
“We found that heightened activation in the amygdala (a region important in initiating our fight, flight, freeze response) to surprised and neutral facial expressions appear to be a vulnerability for developing PTSD, while reduced medial frontal gyrus (a region important in regulating our response to fear) activation appears to be acquired upon developing PTSD,” Hinojosa and Shin told PsyPost.
“Given the importance of the amygdala in fear acquisition and expression, we expected to find exaggerated amygdala responses in PTSD to surprised facial expressions but instead we found it to both surprised and neutral facial expressions,” the researchers added. “This suggests that neutral facial expressions are ambiguous and can elicit amygdala activation in PTSD.”
The study makes an important contribution to the knowledge about neural mechanisms of posttraumatic stress disorder. However, the number of participants in the study was small and all were men and twins who were raised together. Additionally, the study required twins to travel to another city and this meant that only twins who were functional enough to travel could participate.
“While this unique twin study design allows us to uncover the origins of the neural correlates of PTSD, much more work is needed to replicate these findings in larger participant samples,” Hinojosa and Shin explained.
The study, “Exaggerated amygdala activation to ambiguous facial expressions is a familial vulnerability factor for posttraumatic stress disorder”, was authored by Cecilia A. Hinojosa, Michael B. VanElzakker, Katherine C. Hughes, Reid Offringa, Lisa M. Sangermano, Isabella G. Spaulding, Lindsay K. Staples-Bradley, Ethan T. Whitman, Natasha B. Lasko, Scott L. Rauch, Scott P. Orr, Roger K. Pitman, and Lisa M. Shin.