For nearly twenty years my colleagues and I studied post-traumatic stress disorder and the profound negative psychological, social, and neurobiological impact of traumas such as child abuse, natural disasters, physical and sexual abuse, and combat. We often wondered why some survivors succeeded in overcoming adversity, bouncing back, and continuing on with purposeful lives, while others didn't. Some individuals were clearly more resilient than others.
The American Psychological Association defines resilience as "the process of adapting well in the face of adversity, trauma, tragedy, threats or even significant sources of threat." To answer our question, we turned to three groups of highly resilience individuals: former Vietnam prisoners of war, Special Forces instructors, and civilian men and women who had endured and even thrived after surviving harrowing traumas.
In our book, Resilience: The Science of Mastering Life's Greatest Challenges, Dennis Charney M. D. and I systematically address the topic of resilience. Because resilience is the complex product of genetic, psychological, biological, social and spiritual factors, we investigate resilience from multiple scientific perspectives. We synthesize the latest scientific and popular literature on the topic, describe our own psychological and neurobiological research on resilience, and quote from our in-depth interviews with a large number of highly resilient people.
When we began our study, we assumed that resilience was rare and resilient people were somehow special, perhaps genetically gifted. It turns out, we were wrong. Resilience is common and can be witnessed all around us. Even better, we learned that everyone can learn and train to be more resilient. The key involves knowing how to harness stress and use it to our advantage. After all, stress is necessary for growth. Without it the mind and body weaken and atrophy.
Let's take a quick look at some genetic and biological factors that have been associated with resilience. While no one gene or gene variation explains resilience, genetic factors do play an important role in determining how an individual responds to stress and trauma. For example, DNA studies have found that polymorphisms (i.e., variations) of genes that regulate the sympathetic nervous system, the hypothalamic-pituitary-adrenal axis, and the serotonin system partially determine whether our biological response to stress is too robust, too muted, or within a range that is optimal for adaptive functioning. In addition, studies of identical twins, where one twin has been exposed to a traumatic stressor such as combat but the other twin has not, have estimated an overall heritability of posttraumatic stress disorder ranging from 32-38%. This means that genes are important but that they are only part of the story.
A host of neurobiological factors and systems have been associated with resilience including a sympathetic nervous system (i.e., epinephrine and norepinephrine) and a hypothalamic-pituitary-adrenal axis (i.e., cortisol) that respond rapidly to stress and danger but that are well regulated and shut off once the danger has passed; a dopamine reward system that continues to fuel positive emotions even during periods of chronic stress; intact hippocampi that allow us to form new memories, to differentiate between dangerous and safe environments, and help to regulate our stress response; and a highly developed prefrontal cortex that can regulate emotional and behavioral reactivity to stress by inhibiting the amygdala, which plays a central role in processing and triggering raw emotions related to the fight-flight response.
Emerging scientific research has begun to show that neurobiological systems associated with resilience can be strengthened to respond more adaptively to stress. For example, research using EEG and fMRI technology has shown that mindfulness meditation and training in cognitive reappraisal can increase activation of the left prefrontal cortex. This is important because people with greater activation of the left prefrontal cortex recover more rapidly from negative emotions such as anger, disgust, and fear. University of Wisconsin researcher Richard Davidson has proposed that resilience is largely related to activation of the left prefrontal cortex and the strength of neural connections between the prefrontal cortex and the amygdala. Robust activation of the PFC inhibits the amygdala, quiets associated anxiety and fear-based emotions, and allows the PFC to facilitate rational planning and behavior.
As a second example, the hippocampus is another brain region that is critically involved in resilience and how we respond to stress. It is well known that unremitting stress with prolonged elevation of cortisol can damage neurons in the hippocampus. Because the hippocampus helps to regulate the hypothalamic-pituitary-adrenal axis, damage to its neurons can decrease their ability to dampen the stress response. The result may be even greater damage to hippocampal neurons. Fortunately, recent research has found that nerve growth factors, like brain-derived neurotrophic factor, enhance the growth of brain cells, prolong cell survival, and repair damaged nerve cells. In animal studies, vigorous voluntary aerobic exercise increases levels of nerve growth factor and appears to protect against some of the negative effects of stress. This may also be true in humans where research has shown that aerobic exercise can increase hippocampal volume, raise serum levels of BDNF, and improve spatial memory, and that physically active subjects show lower cortisol and SNS responses to psychological laboratory stress compared to less physically active subjects.
As scientists learn more about the complex interplay of genetics, development, cognition, environment, and neurobiology, it will be possible to develop behavioral, social and pharmacological interventions and training programs to enhance resilience to stress.
Steven M. Southwick, MD, a recognized expert on the psychological and neurobiological effects of extreme psychological trauma, is the co-author of Resilience: The Science of Mastering Life's Greatest Challenges (Cambridge University Press 2012). Dr. Southwick is the inaugural Greenberg Professor of Psychiatry, Post-Traumatic Stress Disorder, and Resilience at the Yale Medical School and the Yale Child Study Center, adjunct professor of psychiatry at the Mt. Sinai School of Medicine, and medical director of the Clinical Neurosciences Division of the National Center for Posttraumatic Stress Disorder.