Nov 29, 2021

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For many people, a traumatic experience can leave an indelible impression on the brain in the form of post-traumatic stress disorder (PTSD), which is characterized by hyperarousal and the avoidance of risky behaviors. 


Research has shown that the brain uses distinct circuitries that mediate positive, or rewarding, behaviors and negative, or aversive, ones. PTSD has long been thought to arise from overactivity in the “negative valence system, but a new Tel Aviv University study shows that people with PTSD also displayed a deficit in activation of positive valence processing soon after the trauma, suggesting that it plays a role in resilience to PTSD. 


Positive valence systems are primarily responsible for responses to positive motivational situations or contexts, such as reward-seeking, consummatory behavior in response to a stimulus and that achieves the satisfaction of a specific drive, as the eating of captured prey by a hungry predator, and reward/habit learning. 


Positively valenced emotions are evoked by positive events, objects or situations. Negative valence systems are mainly responsible for responses to aversive situations or context, such as fear, anxiety and loss.


Emotional valence describes the extent to which an emotion is positive or negative. The existence of broad biases that favor more efficient processing of positive or negative emotions is still a controversial matter. 


Prof. Talma Hendler of Tel Aviv University’s School of Psychological Science and the Faculty of Medicine at TAU’s Sagol School Neuroscience worked together with Dr. Ziv Ben-Zion on a study just published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging under the title “Neural responsivity to reward versus punishment shortly after trauma predicts long-term development of post-traumatic stress symptoms.” 


They identified 171 people who had been treated in an Israeli hospital emergency department for a trauma (such as a car accident) and who, within two weeks of the traumatic event, were experiencing symptoms of PTSD. 


One month after the trauma, survivors were assessed in the lab by a trained clinical interviewer in more detail and underwent brain scans by functional magnetic resonance imaging (fMRI). The same assessments were made at six months and 14 months after the traumatic event.


While undergoing fMRI, participants played a competitive electronic gambling game designed to test participants’ sensitivity to risk, reward and punishment. Not surprisingly, participants with more severe PTSD symptoms at the start of the study made fewer risky choices in the game; fMRI scans showed that they had greater activation in the amygdala, a brain region associated with fear processing and a key part of the negative valence system. 


However, reduced activity at one month in the ventral striatum, a mesolimbic brain region involved in processing positive valence like rewards, predicted more severe PTSD symptoms at 14 months.


Ben-Zion said the work “provides insights on roles of both the positive and negative valence processing systems in the early development of post-traumatic psychopathology. While most of the research to date on stress and trauma has focused on the hyper-active negative valence system – increased fear and threat responses — our findings also suggest a critical role for hypo-active positive valence system (less neural activation towards rewards) in PTSD development. They point to its role in resilience to traumatic stress and /or adaptive recovery from it.”


Dr. Cameron Carter, editor of the medical journal, commented that “this work provides new insights into the fundamental changes in brain function that follow traumatic experiences and underlie the development of PTSD. It shows us that these changes go beyond dysregulated threat processing and include brain systems related to reward and motivation that are likely to underlie changes in mood and motivated behavior in PTSD.”


The work could have implications for therapeutic strategies to treat stress- and anxiety-related disorders, Hendler said, adding that “novel therapeutic approaches should address both positive and negative valence systems, as these two are intrinsically linked and both affect the symptom development after experiencing traumatic stress. Furthermore, we suggest that specific deficits in each valence system are associated with specific symptoms of PTSD, possibly pointing to distinct underlying mental processes that could guide a more personalized approach in psychiatric treatment.”