Introduction

Individuals who experience a moderate-to-severe Traumatic Brain Injury (TBI) may exhibit a wide spectrum of outcomes, from remarkable recovery to profound disability. Mental health, physical health, and overall well-being are frequently affected, and research suggests that these problems may persist long after the injury [1]. Despite advancements in neuroimaging, much of the variability in TBI outcomes remains unexplained. Resilience, usually defined as positive outcome despite adversity [2], is currently understood as a dynamic process that harnesses biological, psychosocial, and cultural resources to support positive adaptation to change [3,4,5,6,7,8,9]. Factors that confer resilience encompass personal qualities, as well as individual, social, and community resources. Individuals who face life’s hardships with courage and perseverance, maintain a positive outlook under difficult circumstances, and foster supportive social bonds epitomize resilience.

This narrative review surveys the existing literature on resilience factors that influence outcomes of moderate to severe TBI. It explores individual factors such as personality traits, co** styles, and premorbid psychiatric or medical history. Additionally, this review delves into the importance of social support, including aspects such as the quality and quantity of support networks, experiences of social isolation or loneliness, and caregiver burden. Furthermore, we examine the influence of social determinants of health, encompassing factors like race and ethnicity, socioeconomic status, neighborhood characteristics, and access to healthcare resources. Lastly, we discuss pathways to resilience and strategies for building resilience post-TBI, with a focus on clinical applications and potential targets for intervention. By synthesizing and analyzing research across these domains, this review aims to provide valuable insights into understanding and enhancing outcomes for individuals affected by moderate to severe TBI. The factors related to resilience discussed in the present review are summarized in Table 1.

Table 1 Factors impacting resilience in TBI

Individual Factors Conferring Resilience

Personality traits are thought to be stable and enduring characteristics that describe an individual’s patterns of thoughts, feelings, and behaviors. Researchers operationalize and measure these traits to better understand and predict a person’s behavior in various situations. They are typically measured on a continuum, meaning each person possesses each trait to varying degrees rather than simply having or not having them. Personality traits have been associated with resilience in a range of populations [10]. Most commonly, personality is operationalized using the five-factor model [11], in which personality is delineated along the following dimensions: neuroticism, extraversion, openness, agreeableness, and conscientiousness. In the general population, resilience is negatively associated with neuroticism, yet shows some positive association with the dimensions of extraversion, openness, agreeableness, and conscientiousness [10, 12]. Research in individuals with a history of moderate to severe TBI supports the idea that these personality traits may be important for resilience after brain injury as well. For example, higher extraversion and lower neuroticism are associated more broadly with better post-TBI functional outcomes [13, 14].

In addition to relatively stable personal qualities, dynamic behavioral and psychological processes, such as the application of co** strategies, also play an important role in adjustment post-injury. For example, cultivation of present focused mindset /mindful awareness of the present moment has been shown to confer resilience in those who have sustained TBI [15,16,17]. Cultivation of gratitude and optimism are similarly related to mental health outcomes in TBI [18, 19].

Evidence suggests that TBI-related sequelae may themselves interfere with an individuals’ ability to enact adaptive co** strategies. In individuals with a history of TBI, there appears to be an increase in emotion focused co** strategies—generally associated with poorer psychosocial outcomes, relative to problem focused co** strategies—generally associated with better psychosocial outcomes [20]. Further, those with TBI- related alexithymia, an inability to identify and express one’s feelings, are more likely to express avoidance co** strategies [21]. These findings suggest that individuals with moderate to severe TBI may benefit from additional support to utilize more adaptive co** strategies, which is a potential avenue for intervention.

Other aspects of life-experiences and personal history that individuals bring to their injury also impact resilience following TBI. Preinjury history of mental health conditions increases the likelihood of develo**/expressing mental health symptoms post injury [22]. This is seen across the spectrum of TBI [23]. For example, pre-injury mental health treatment is a risk-factor for develo** depression after moderate to severe TBI [24]. Regarding substance use disorders, there is a bidirectional relationship with TBI, with substance use increasing the risk of sustaining a TBI, and TBI impacting post-injury substance use. Alcohol use is the one of the strongest predictors of sustaining a TBI [25], and furthermore, history of premorbid substance use is associated with worse mental health outcomes post injury [26]. Although alcohol use following TBI is further associated with poorer functional and mental health outcomes, this relationship is somewhat muddied by a paradoxical relationship between post-TBI alcohol use and injury severity, with more severe injuries associated with less substance use [27], a finding which is thought to reflect the fact that those with more severe injuries are more likely to require assistance in daily activities (e.g. transportation, shop** etc.) which in turn limits access to substances.

Adverse Childhood Experiences (ACEs) are potentially traumatic events that occur in childhood, such as abuse, including sexual, emotional and physical abuse or neglect, and household/environmental factors, such as household mental illness/substance abuse, witnessing intimate partner violence, or incarceration of household member. A strong correlation has been found between ACEs and a wide range of long-term health problems, including chronic diseases such as heart disease, diabetes, and cancer, as well as mental health issues like depression, anxiety, and PTSD [28, 29]. ACEs have compounding risk for poor TBI outcomes, as they are associated with increased risk of sustaining a TBI and poorer psychosocial outcomes after injury. In a recent study surveying 3454 individuals, individuals who have experienced three ACEs, they were more than 4 times more likely to experience a TBI than those without ACEs [30]. In particular, history of sexual abuse, physical abuse, mental illness in a household member, and having a household member who was incarcerated were specifically linked to TBI risk [30]. Although more research is needed, a history of ACEs is linked to negative mental health outcomes in numbers studies [31]. Particular care in assessing mental health of those with TBI and ACEs history is warranted.

Social Factors Conferring Resilience

In addition to the impact of internal psychological factors and pre-injury characteristics, there is a breadth of literature indicating the significant impact of social resources on outcomes following moderate-to-severe TBI [32].

Following moderate-to-severe TBI, decline in cognition, functional independence, and emotional processing can lead to difficulties in social role functioning and engagement in community activities. Aspects of social and community engagement that are susceptible to change after TBI include active participation in immediate community activities, including home operations, as well as participation in activities outside of the home, such as social events, as well as engagement in volunteer, educational, or vocational settings [33]. Community integration is associated with both subjective and objective markers of resilience following TBI; it has been found to be positively associated with life satisfaction, and inversely related to emotional distress [34, 35]. Additionally, a greater degree of community integration has been associated with greater levels of support from loved ones, and a return to meaningful work [36, 37]. Conversely, lower levels of community integration following TBI are associated with social isolation [38]. Notably, social isolation is itself associated with poor outcomes [39]

Difficulties maintaining interpersonal relationships and the experience of social isolation have emerged as deleterious factors leading to diminished resilience following TBI [15]. In communities with reduced resources, loneliness is associated with poor mental health, stress, anxiety, and depression [39]. As a result of cognitive, emotional, and functional changes, relationships with friends, spouses, children, and parents shift following a moderate-to-severe injury, and previously integral social outlets become more challenging to access and engage with [40,41,42]. Following TBI, individuals experience a drastic decrease in reported number of friends and the frequency of social contact [43, 44]. TBI survivors have been found to be less active in social and recreational activities, and there is a higher degree of subjectively reported social isolation in this population, regardless of age [45, 46]. Furthermore, persons living with TBI report that they are aware of the impacts of long-term cognitive and behavioral changes on social interactions, and attribute these to loss of their pre-injury friendships as well as difficulties making new friends [47].

There have been numerous studies underscoring the impact of the decline in social engagement and support following TBI. The subjective experience of social isolation and romantic loneliness have been found to predict changes in quality of life, emotional well-being, depression and anxiety [32, 48]. Research suggests that reduced quantity and depth of social relationships directly impact well-being, and also partially account for the association between life satisfaction and injury severity [49]. In the years following brain injury, individuals who were married or partnered reported significantly higher quality of life than those who were single [50]. Notably, psychosocial support, and more specifically emotional support, has been identified as the most common type of support needed by survivors of TBI, above support with basic and instrumental activities of daily living, irrespective of level of disability. Moreover, the need for social support has been found to increase over time, particularly between 3-and-5 years post-injury [51]. However, in addition to getting along with others and availability of emotional support, receiving assistance in the completion of activities of daily living is positively associated with quality of life in the years following brain injury [50].

The majority of individuals living in the community following moderate to severe TBI require daily assistance in their functioning [52]. Approximately 80% of individuals return to a home-setting, although the provision of functional assistance and social support often falls on the shoulders of family members and other informal caregivers regardless of residential setting [53, 54]. Following brain injury, family members are often the long-term primary caregivers of those with functional disability [55, 56]. The families caring for persons with TBI at home often live in situations characterized by multiple unmet needs, and these can be a source of poor health outcomes for injured individuals and their families [57].

There is a growing body of literature illuminating how unmet needs of TBI-caregivers impact caregiver burden and influence psychological and functional outcomes of the individuals they care for. There are numerous factors impacting caregiver stress, including reduced privacy and time to themselves, increased anxiety, sleep changes, adjustments to finances, and changes in social relationships [58]. Understanding and ameliorating the stress of caregiving following brain injury is integral to caregiver wellness, which has been found to be related to patient wellness. Research shows that patient and caregiver wellness are linked, and social support of caregivers contributes to their psychological well-being and better mental health, social, and community integration outcomes for those that they care for [40, 59, 60]. In addition to psychosocial outcomes, functional outcomes have also been found to be impacted by caregiver wellness. One study found that emotional distress in caregivers was associated with the quality and quantity of caregiving, their attitudes regarding neurorehabilitation and compliance with professional guidance, and to the functional recovery of their loved ones [61].

Social Determinants of Health

Social determinants of health (SDoH) represent many individual and societal factors which have been strongly linked to variance in health outcomes. SDoH are broadly grouped into five domains: economic stability, education access and quality, health care access and quality, neighborhood and built environment, and social and community context [62]. While factors of every domain intersect to form unique circumstances and identities more complex than any one descriptive factor, examining components within each domain has provided insight on how SDoH is linked to resilience in individuals with TBI.

Within social and community context, racial and ethnic identity is the most well-examined SDoH factor impacting health outcomes following TBI [63]. Racial disparities in resilience factors emerge early in the course of recovery, with race being significantly correlated with what kind of post-acute care individuals with TBI receive. White individuals, for example, are more likely to receive outpatient rehabilitation care focused on higher-level functional goals and community participation. Conversely, Black individuals receive more home health care, which focuses on daily living inside of a home environment [64]. Outside of healthcare settings, white and non-white individuals have been found to have significantly different functional outcomes following TBI. Non-white racial identity has been found to have a negative correlation to both Functional Independence Measure score (FIM) and measures of community integration following injury [65, 66]. While race is a well-documented determinant of post-TBI outcomes among SDoH factors, the mechanisms that account for these well-documented associations have not been well studied.

Another well-investigated SDoH in TBI resilience is insurance coverage. While coverage is inextricably linked to a web of other social factors including age, income, and employment status, its effect on resilience measures such as functional scores at discharge from acute rehabilitation remain robust even when controlling for these covariates. In a Traumatic Brain Injury Model Systems (TBIMS) study of 8558 individuals admitted to inpatient rehabilitation, payer source was found to have a significant effect on FIM score at discharge, independent of demographics and injury characteristics [67]. In another study, payer source remained a significant correlate of functional status as assessed by Disability Rating Scores (DRS) at 1-, 2-, and 5-years post-injury [68]. In both studies, lack of any medical insurance or public insurance coverage such as Medicaid was associated with lower functional status scores than private insurance coverage [67, 68].

Economic stability, as described by employment and broader socioeconomic status, is also correlated with resilience in TBI recovery. Pre-morbid employment type is significantly correlated with outcomes at 6 months post injury, with identifiable differences in outcomes among those defined as blue collar, white collar, or self-employed workers as well as individuals who were retired, unemployed, or classified as students at time of injury [69]. Post-morbid employment is also closely tied to reintegration into society and mental health in TBI recovery. One of the most pertinent examples of the impact of post-injury employment on resilience is the disparity in suicidality rates in employed and unemployed individuals with TBI. Individuals who self-reported being employed at one year and two years post-injury were significantly less likely to report suicidal ideation than those who reported unemployment [70]. In a broader scope than employment status alone, potential resilience is stratified by higher and lower socioeconomic status. When operationalized by the Indices of Multiple Deprivation (IMD), lower socioeconomic status was associated with poorer Extended Glasgow Outcome Scores (GOSE), despite not being associated with poorer GCS score at time of injury [71].

There is a growing appreciation that the broader neighborhood structure and built environment in which an individual lives is a major determinant of longevity, health, and well-being. Emerging research is beginning to elucidate how these factors influence recovery from TBI. Variability in physical proximity to health care facilities and the accessibility of transportation and community resources are particularly salient for individuals living with disability. The disparity in post-TBI outcomes between individuals living in urban and rural areas is well documented. One study comparing outcomes for rural and urban dwelling moderate to severe TBI patients in Japan found that individuals living in rural areas not only had higher in-hospital mortality rates than their urban counterparts, but also did not achieve independence in activities of daily living as frequently [72]. Neighborhood-level socioeconomic status has also been found to impact post-TBI outcomes. Children who had experienced TBI, for example, were found more likely to develop epilepsy when living in neighborhoods classified as deprived compared to those classified as non-deprived [73]. Built and natural environment have also been linked to the availability of information and technology to those recovering from acquired neurological insults including TBI, secondarily influencing participation rates [74]. While the pool of literature investigating the relationships between living environment and general health outcomes is rapidly expanding, further research into TBI specific outcomes would be beneficial.

Pathways to Building Resilience

There are important clinical applications of this growing body of literature on resilience science as applied to TBI. Most broadly speaking, a focus on resilience means departing from deficit-centered approaches and moving towards interventions that take a strength-oriented model, “building what’s strong” rather than “fixing what’s wrong.” While understanding risk factors remains important, resilience-focused intervention frameworks focus on identifying and bolstering positive attributes, assessing contextual strengths, and cultivating support. Resilience-based interventions aim to enhance patients’ access to resources while building their personal capacities to adapt to their conditions and contexts. Crucially, such resilience-focused approaches should not overlook the imperative of addressing systemic injustices or mitigating preventable risks like experiences of discrimination or exposure to violence, recognizing that safeguarding against harmful experiences is foundational to nurturing resilience in individuals recovering from TBI.

To date, most of the work towards develo** resilience-building interventions for TBI has focused on the individual person-level. For example, Kruetzer and colleagues developed Resilience and Adjustment Intervention (RAI) for individuals recovering TBI. RAI is a comprehensive program aimed at bolstering resilience and aiding adjustment, through a combination of education, skill-building, and psychological support. RAI targets key areas such as emotional regulation, stress management, problem-solving, and communication, addressing concerns commonly identified by individuals with TBI to foster a resilient profile. A randomized controlled trial found that RAI significantly increased resilience compared to a wait-list control group. Secondary measures also indicated improvements in psychological health and adjustment, with observed maintenance of gains at a 3-month follow-up [75]. While this intervention is one of the few explicitly aimed towards building resilience, there are numerous other interventions targeted towards supporting self-management [76,77,78], develo** problem solving skills [79, 80], and fostering and supporting caregiving relationships [81].

From a social perspective, identifying effective interventions to support the social needs of individuals and their caregivers following TBI may improve adjustment and co** for persons living with TBI and their caregivers alike. A recent systematic review highlighted the benefits of long-term participation (i.e., greater than 9 sessions) in peer-support groups for individuals following TBI in adjusting to their injury outcomes [82]. Additionally, there have been developments in resilience-based caregiver interventions following TBI; One study found that an approach including education regarding neurorehabilitation following TBI, self-management of stress and anxiety, and ways of co**, as well as the provision of emotional support for caregivers led to a greater number of self-reported needs met [83]. Another study found that peer-support groups were helpful in reducing symptoms of depression and improvements in stress for caregivers [84]. These interventions would be expected to lead to improvements in outcomes for those they care for, in addition to direct caregiver benefits [40, 59, 61].

Work toward develo** interventions that address neighborhood and community factors to promote resilience after TBI remains in its infancy. From a social determinants perspective on resilience and TBI, it is crucial to recognize that individual-level interventions cannot combat systemic inequities that influence social determinants of health. Promoting resilience post-TBI necessitates social, community, and policy-level interventions [85]. Programs and interventions aimed at fostering resilience should complement public health measures that address the social determinants of health, as suggested by a recent study demonstrating that the availability of state supports for persons with brain injury was associated with better health outcomes [86]. Adopting a whole community approach to resilience is essential for bridging the gap in public health policy.

Conclusion

While the study of resilience has significantly advanced our understanding of developmental psychopathology and responses to adversity in general, relatively little research has extended this work to the study of TBI. The study of resilience in the context of brain injury recovery is a growing area of interest. Emerging work has shown that higher levels of resilience are associated with decreased rates of depression and anxiety; and increased life satisfaction and community participation following TBI [87, 88].

Understanding resilience in the context of TBI requires conceptual frameworks that account for reciprocal relationships across multiple levels of analysis. Resilience is influenced by a myriad of factors including genetics, neuroendocrine processes, individual traits, social support systems, community dynamics, and public policies, which are intricately interconnected [89]. Conceptual models that elucidate the reciprocal influences of these factors are crucial for comprehensively understanding and effectively addressing resilience in individuals affected by TBI.

Interventions at both individual and interpersonal levels have shown promise in fostering resilience among children and adults. However, there is a scarcity of interventions aimed at bolstering community-level resilience, despite their potential effectiveness. At the individual level, there is evidence that behavioral interventions can boost resilience after TBI, and incorporating resilience-focused interventions into rehabilitation may offer promising avenues for enhancing overall functioning and promoting better adjustment post-injury. Moreover, positive psychology constructs such as hope, optimism, and adaptive co** have gained attention for their potential role in augmenting existing therapies and promoting resilience in the face of adversity.