The ‘Resilient Brain’: challenging key characteristics associated with the concept of resilience

Resilience is a psychological construct broadly defined as positive adaptation in response to adversity (Fletcher & Sarkar, 2013). Resilient people do not despair or distract themselves from difficulties, but instead face them head-on. What makes some individuals more resilient than others is thought to rely on psychological mechanisms such as abilities to cognitively and emotionally cope with negative emotions. The corpus callosum provides interhemispheric connections, specifically to cognitive pathways, which allow for faster processing and reflection and has been identified as a key neural substrate of resilience (Edwards, Sherr, Barkovich, & Richards, 2014; Etkin, Egner, & Kalisch, 2011). Galinowski et al. (2015) have shown greater anatomical connectivity within the anterior body of the corpus callosum in resilient adolescents with high exposure to lifetime stress compared with non-resilient adolescents exposed to the same level of stress and healthy control adolescents from the same community. Converging neuroimaging evidence has further shown reduced volume of the corpus callosum in stress-related and major psychiatric disorders such as depression and treatment-resistant schizophrenia (Sun, Maller, Daskalakis, Furtado, & Fitzgerald, 2009). These studies highlight an association between resilience and structural integrity of the corpus callosum, with particular emphasis on the cognitive resources it subserves (Galinowski et al., 2015). Other characteristics typically used in the conceptualization of resilience are extraversion, openness to experience, self-efficacy and agreeability (Fletcher & Sarkar, 2013; Galinowski et al., 2015). However, protective factors are largely built on the assumption that resilient individuals actively work through the problems they face (Luthar, 2006; Luthar & Cicchetti, 2000; Luthar, Cicchetti, & Becker, 2000). Here, we call into question this widely held assertion by presenting a case of a fully functioning middle-aged man, T.C. , who is not only unaware of his congenital absence of the corpus callosum, but also refutes key traits that are commonly associated with the concept of resilience. When enrolled to a neuroimaging study, T.C. showed characteristics typical of a healthy volunteer. He was well-educated and had a normal IQ, stable employment, no childhood adversity and good mental and physical health (online Supplementary Table S1). However, structural magnetic resonance imaging of his brain revealed total agenesis of the corpus callosum (AgCC), a rare birth defect, characterized by a partial or complete absence of the bundle of fibres that connects both cerebral hemispheres (Fig. 1a, b). Less than seven in 1000 people are thought to be affected by this condition, most of whom are diagnosed early in life due to experiences of severe developmental disabilities, seizure disorders, cognitive deficits and social difficulties despite otherwise normal intelligence (Paul et al., 2007; Siffredi et al., 2018). Nonetheless, T.C. remained asymptomatic and was leading, by several measures, a healthy and successful life. T.C. ’s case is remarkable, particularly when considering his cognitive and emotional profile with respect to the AgCC and malformation of the basal ganglia and other grey matter structures (Fig. 1a, b). T.C. ’s performance on working memory and attentional-set shifting tasks fell within normal range (online Supplementary Table S1), but his self-control, as indexed by the Stop-Signal Reaction Time (SSRT) during stop-signal task performance, was above the average of his 55 healthy peers participating in the same study (Fig. 1c). Given that the ability to suppress unwanted or inappropriate thoughts and actions is critical for adaptive behaviour (Verbruggen et al., 2019), good self-control may be one higher-order executive function that is particularly important for helping vulnerable individuals overcome their difficulties. For example, trauma-exposed individuals who successfully control their negative memories by over-activating top-down inhibitory control networks do not develop post-traumatic stress disorder (Mary et al., 2020). Likewise, at-risk individuals, who despite a family history of drug addiction do not succumb to addiction themselves, also over-activate the prefrontal inhibitory network when controlling their thoughts and behaviour (Ersche et al., 2020; Morein-Zamir,