Contents lists available at ScienceDirect Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy Psychological flexibility: A psychological mechanism that contributes to persistent symptoms following mild traumatic brain injury? Josh W. Faulkner a,d, ⁎ , Alice Theadom a , Susan Mahon a,d , Deborah L. Snell b , Suzanne Barker-Collo c , Kay Cunningham d a TBI Network, Auckland University of Technology, University of Technology, 90 Akoranga Drive, Northcote, Auckland, New Zealand b University of Otago, Christchurch, 2 Riccarton Ave, Christchurch 8011, New Zealand c Auckland University, Auckland CDB, Auckland 1010, New Zealand d Proactive Rehab, Wakefield Specialist Centre, Florence Street, Wellington 6021, New Zealand ARTICLE INFO Keywords: Mild traumatic brain injury Psychological flexibility Post-concussion symptoms Recovery ABSTRACT Persistent symptoms following a mild traumatic brain injury (mTBI) can have profound implications on all aspects of an individual’s functioning. Psychological factors have a significant role in contributing to the de- velopment of persistent post-concussion symptoms and predicting outcomes. Biopsychosocial explanations have therefore been applied to prognostic models of mTBI. What is not evident in the literature to date is an un- derstanding of the psychological mechanisms that may be important in mediating the various psychological factors in these models. The construct of psychological flexibility holds promise in this regard. Psychological flexibility is the ability to act in alignment with values in the presence of inner discomfort such as pain and distress. It is hypothesised that psychological flexibility has a significant role in the development and main- tenance of persistent symptoms following mild traumatic brain injury. The rationale that forms the basis of this hypothesis is as follows: a relationship exists between psychological flexibility and pre-injury psychological risk factors; psychological flexibility is vulnerable to the pathophysiology associated with mTBI; post-injury psy- chological and neuropsychological factors exacerbate and maintain psychological inflexibility; and psycholo- gical flexibility underlies psychological responses to mTBI that contribute to unfavourable outcomes. A dis- cussion of the literature that pertains to each of these points is presented. Based on this hypothesis, we conclude, that there is rationale to empirically explore the role of psychological flexibility in mTBI and its relationship to outcomes. This may also lead to evaluation of specific interventions that target this psychological mechanism in mTBI, such as Acceptance and Commitment Therapy, and improve outcomes for this population. Introduction Psychological flexibility Psychological flexibility has been proposed as being a fundamental aspect of health and wellbeing [49]. It can be defined by how one adapts to changing situational demands, allocates mental resources, shifts perspective, and finds balance amongst competing demands [49]. In broad terms psychological flexibility compromises three compo- nents: “… the capacity to 1) persist or to change behaviour in a way that includes conscious and open contact with thoughts and feelings [openness], 2) appreciate what the situation affords [awareness], and 3) serve one's goals and values [engagement]” [79].) Psychological flexibility results in a person being more open and willing to experience discomfort from difficult internal and external experiences. This miti- gates avoidance and allows the individual to behave more in ac- cordance with values, despite the potential for encountering difficult or uncomfortable sensations. High levels of psychological inflexibility have been associated with poor psychological health and measures of psychological flexibility are related to a number of self-report measures of mental health [13,19,73]. Such associations have been established in depression [9], eating disorders [21,87], anxiety and pathological worry [39,105], psychosomatic symptoms [60,74], chronic pain [79,113], psychosis [91] and substance disorders [67]. Recently, a re- lationship between psychological flexibility and rehabilitation ad- herence has also been documented [24]. Consequently, psychological https://doi.org/10.1016/j.mehy.2020.110141 Received 19 May 2020; Received in revised form 18 July 2020; Accepted 23 July 2020 ⁎ Corresponding author at: Department of Psychology, School of Clinical Sciences, Auckland University of Technology, 90 Akoranga Drive, Northcote, Auckland, New Zealand. E-mail address: josh.faulkner@aut.ac.nz (J.W. Faulkner). Medical Hypotheses 143 (2020) 110141 0306-9877/ © 2020 Elsevier Ltd. All rights reserved. T