As clinicians and the public move from a pathological (disease-focused) to a salutogenic (health-focused) understanding of the human condition, protective factors contributing to the health of individuals and societies have received more attention. The study of resilience is a foundational aspect of this critical shift and a promising way to understand and interpret our responses to complex multi-domain perturbations from stressful and traumatic experiences. However, as researchers from different fields engage in resilience research, a plethora of definitions and understandings have emerged requiring detailed academic discourse. Rapidly changing global, political, economic and environmental circumstances highlight the need for effective solutions to understand and enhance resilience. These solutions require a multidisciplinary understanding of the concept of resilience.
In January 2012, Samueli Institute convened a meeting entitled ‘Towards a systems model of resilience: state of the science and future directions’ held at the National Academy of Sciences' Beckman Center to help bridge the current gaps in understanding interdisciplinary approaches to the study of resilience and to encourage cross-discipline dialogue on the potential promise of creating systems models of resilience. Prominent scientists in scientific fields such as systems biology, systems engineering, mathematics, biology, psychoneuroimmunology, psychoneuroendocrinology, sociology, medicine and psychology, along with key Department of Defense leaders, gathered to both share perspectives and explore the possible utility of creating interdisciplinary, systems-based models for understanding resilience. The meeting was highly successful in engendering collaborative education and enthusiasm for forwarding the study of resilience in an interdisciplinary and systems-oriented fashion. In this Theme Issue of Interface Focus, we summarize findings that arose from a first major effort to explore resilience from a diversity of disciplines and perspectives. The culmination of these efforts is a rich tapestry of views, ready to be woven into a coherent whole.
The classical Latin-origin definition of resilience (resili (ens), present participle of resilire—to spring back, or rebound) was used to describe the tensile properties of material objects (also known as elastic memory) such as wood and metals . This conceptualization of resilience is understood as ‘recoiling’ to an original state after a perturbation. Since the use of the term in the early 1800s, the concept of resilience has been applied to many fields of human endeavour, including the study of ecosystems and human responses to adverse conditions such as natural disasters, war and personal loss . Although this Theme Issue is focused on the domain of health-oriented resilience, the study has expanded to include many disciplines such as politics, diplomacy and economics, to name a few.
While the interest and efforts in studying resilience expand, our understanding of what resilience is and how best to enhance it in various contexts remains fragmented. A consensus definition of the term resilience has not come to fruition, although several themes emerge from the existing data. A literature search conducted by the RAND Corporation unearthed 122 definitions of resilience. Three major themes emerge from these varied definitions that indicate our current understanding of resilience as (i) a dynamic process (rather than as a ‘trait’) that evolves across time, (ii) adaptability to change and, generally, to adversity, and (iii) either a return to homeostasis, or an enhanced state of functioning (e.g. growth) . When examining resilience as a response to adversity, our current understanding needs to expand beyond the concept of a return to homeostasis, to instead a new normal that is characterized by stability through change. Being resilient entails more than the ability not only to adjust and adapt to a perturbation, but also to transform when the perturbation requires a new conceptualization of the way in which to effectively proceed forward. This process does not return an individual or system to a previous homeostatic set-point. Rather, the concept of resilience uses learning from prior experiences to effectively adapt by anticipating and predicting current needs, and modifying feedback inputs to achieve maximal efficiency of that system within a particular context and timeline. This evolution in understanding resilience from a dynamic perspective is consistent with a control systems model of allostatic, versus homeostatic, regulation . The relationship between adversity and enhanced resilience has been documented previously; non-specific resilience is enhanced by prior moderate stressors [5–7]. In other words, resilience does not occur and cannot be detected outside of a stressor or changing context. However, individuals with a history of high adversity report decreased well-being and psychological functioning. The act of being resilient is an adaptive response to stressors that is, ultimately, dependent on context. The most common reaction and/or response to a traumatic incident is resilient behaviours: ‘although symptom levels tend to vary for different potentially traumatic events, resilience has consistently emerged as the most common outcome trajectory' [8, p. 136].
Fully understanding resilience requires systems approaches that facilitate the modelling of dynamic interactions in multiple domains (e.g. psychological, physical and social) within a person and between his or her social and physical environment. There is an increasing interest in systems-based approaches to understanding resilience between people and their surrounding environments, such as those in socio-ecological systems [9,10]. Reductionist approaches used by some researchers when developing and testing hypotheses about resilience separate the person from his/her environment or subjugate the environmental variable when performing analyses. In these analyses, the environment only becomes an important variable when ‘it provides a forum in which resilience-promoting-processes that contribute to individual growth take place' [11, p. 4]. As a consequence, outcomes remain void of cultural, historical and political constructs .
The structure of our current academic systems facilitates highly specialized, narrowly focused disciplines that often do not promote opportunities to effectively communicate across fields of study. Specialization generates monumental progress within our isolated fields of discipline and allows us to use more precise tools for examining parts of the whole. However, it also constructs barriers to integrated thinking required for solving complex scientific puzzles such as resilience. Ongoing cross-discipline dialogue will be essential for fostering a complete understanding of resilience within the whole person and his/her environment. Models of resilience that incorporate mental, emotional, social and physical processes will be maximally effective in helping understand and enhance resilience within individuals and societies.
The meeting held addressed the pressing need to induce dialogue across various disciplines and among academics studying resilience. The publications in this Theme Issue of Interface Focus on resilience reflect some of the thinking and research on resilience from academic experts who attended, as seen through their particular scientific lens. Several articles reflect the promise of systems-based modelling approaches for helping solve issues related to physiological resilience. We now move to a discussion of these articles, starting with the articles that describe the value of systems modelling approaches to understanding resilience in medical and physiological settings. We then continue our discussion noting the articles that discuss systems thinking surrounding mind–body interventions for enhancing resilience, and conclude with the articles that discuss resilience within military contexts and other social settings.
Csete & Doyle's  article, ‘The mathematician's toolbox for management of type 1 diabetes’, offers a non-technical summary of the utility of control systems modelling in the development of the artificial pancreas, noting both its promise and shortcomings. It also provides the reader with an opportunity to reflect on the utility of control engineering tools to better understand and enhance resilience within medical settings. Aschbacher et al.'s  study entitled ‘The hypothalamic–pituitary–adrenal–leptin axis and metabolic health: a systems approach to resilience, robustness and control’ further explores the utility of control systems tools and thinking in its exploration of robustness as a key indicator of stress system resilience. This study employs relatively simple, yet novel systems-based mathematical tools to examine the dynamics of the HPA–leptin feedback sensitivity—these dynamics predicted metabolic risk in the population studied, whereas traditional neuroendocrine measures did not. The study, along with Aschbacher's previous work, points to the promise of using dynamic systems modelling approaches in the field of psychoneuroendocrinology to better understand mind–brain–body relationships as they relate to resilience.
Vodovotz's  article, ‘Computational modelling of the inflammatory response in trauma, sepsis, and wound healing: implications for modelling resilience’, also speaks to the promise of employing systems modelling approaches to the study of sepsis, an acute inflammatory response to a noxious agent that can be life-threatening. This article provides an overview of the relevance of both data-driven and mechanistic models for understanding and predicting acute inflammation, and suggests the promise of integrating both approaches for understanding inflammation that may be used clinically. Vodovotz provides a provocative hypothesis that inflammation may be a key factor in understanding resilience at the whole organism, under the skin, level, and proposes some methods by which this hypothesis could be tested.
Irwin's  review on ‘Sleep and inflammation in resilient aging’ builds on this theme by discussing the complex relationships between sleep, inflammation and resilient aging, noting that high versus poor sleep quality may act as a resilience-enhancing or perturbing factor, respectively, within the context of aging. Irwin reviews the data for sleep's relationship to resilient aging as well as its relationship to resilience-interfering factors such as depression, pain, morbidity and mortality in the elderly. Irwin further suggests that proper sleep may buffer increases in inflammation that are found for aging populations, speaking to the promise of behavioural interventions that improve sleep quality as a method of enhancing psychobiological resilience in the elderly.
Similarly, in Silverman & Deuster's  review, ‘Biological mechanisms underlying the role of physical fitness in health and resilience’, the biological systems that may underlie the impact of physical fitness on resilience and health are discussed. The authors suggest that physical fitness may enhance psycho-physiological resilience through multiple pathways, including by optimizing neuroendocrine and psychosocial reactivity to stressors, as well as by reducing tonic levels of inflammation and enhancing neuroplasticity and growth factor expression. Similar to Irwin, the authors call for the need for easily implementable behavioural strategies such as exercise to enhance human resilience, as a self-modifiable characteristic.
Understanding resilience includes investigating key biological factors that may play a role in identifying resilience within the context of traumatic stress. This is a key to helping individuals who are required to engage in highly stressful and life-threatening scenarios such as war fighting, disaster scene search and rescue, civil disturbance response, fire and police work. The thoughtful and thorough commentary by Litz  entitled ‘Resilience in the aftermath of war trauma: a critical review and commentary’ illustrates the complexity of understanding resilience in the context of war trauma, and speaks to the need for us to carefully develop effective assessment, prevention and treatment strategies to enhance resilience to war trauma within various contexts and across the deployment cycle.
Yehuda et al.'s  article also discusses resilience factors within the context of traumatic stress. In the article, ‘Glucocorticoid related predictors and correlates of post-traumatic stress disorder treatment response in combat veterans’, the authors examined the potential relevance of glucocorticoid variables in predicting responses to psychotherapeutic treatment for post-traumatic stress disorder (PTSD). Interestingly, the study indicated that both prolonged exposure and a minimal attention control considerably reduced PTSD symptoms over time. Genotype for the glucocorticoid receptor (BCLI polymorphism), as well as pre-treatment levels of neuropeptide Y, predicted treatment responses, and 24 h urine cortisol levels as well as glucocorticoid sensitivity appeared to be sensitive biomarkers of change in response to the intervention. The study indicates the promise of systems-oriented approaches (psychoneuroendocrinology) in linking mind–body processes associated with resilience and the potential value of neuroendocrine biomarkers in predicting risk and resilience to PTSD. Finally, related to systems models on social resilience, Pincus's  article, ‘One bad apple: experimental effects of psychological conflict on social resilience’, demonstrates both the impact of individual-level conflict on higher-order (group) systems, and the value of dynamic analyses in assessing potential ‘ripple effects’ related to the social domain of resilience.
This tapestry of articles reflects the varied approaches and levels of investigation that are apparent in understanding human resilience today. We note that this is far from a complete representation of the breadth of the current theory and investigation that comprises the study of resilience. It does not at this point reflect the integration of cross-discipline thinking and collaboration that the future may hold. However, the integration of these multiple perspectives on resilience as reflected is the first necessary step towards a truly whole systems model of resilience. We are confident that the breadth and overlapping nature of the current articles will be both informative and interesting to the reader and help the scientific community better understand the current terrain of inquiry surrounding the study of resilience.
This Research program is supported by DoD/TATRC W81XWH1120173, entitled ‘Central Evaluation of Resilience Programs (CERP)’.
One contribution of 9 to a Theme Issue ‘Towards a systems model of resilience’.
- © 2014 The Author(s) Published by the Royal Society. All rights reserved.