A minimal model of PTSD susceptibility and timescales

Post-traumatic stress disorder (PTSD) is a debilitating condition marked by persistent intrusive memories, hyperarousal, avoidance, and cognitive and mood disruption following trauma. Despite substantial research, treatment outcomes remain varied, and mechanistic understanding remains incomplete. PTSD involves maladaptive memory consolidation and dysregulation of limbic circuits, autonomic nervous system, and endocrine axes. A hallmark feature is that only 20-30% of trauma-exposed individuals develop chronic symptoms, while others recover over widely varying timescales ranging from days to months. Given the complexity of PTSD physiology, a minimal dynamical model can distill essential features and clarify how core mechanisms give rise to long-term outcomes. Here, we present a minimal dynamical model featuring an autocatalytic symptom driver balanced by a removal process. The model captures the bistability of PTSD, in which trauma causes a persistent switch to a high-symptom state. It accounts for the susceptibility to PTSD using a single non-dimensional “resilience" parameter R that characterizes individual differences (assumed to vary in the population due to genetics and early life experience) that exceed a threshold in resilient individuals and fall below a threshold in those susceptible to PTSD. The model provides a natural explanation for the broad distribution of timescales when R approaches the threshold for PTSD susceptibility - a dynamical ghost phenomenon. It also predicts a critical threshold for treatment efficacy: only interventions that sufficiently reduce symptoms below a threshold lead to lasting recovery, consistent with clinical findings, including hyperbaric oxygen therapy. This simplified framework links physiological mechanisms to the nonlinear dynamics of trauma response and may inform individualized treatment strategies.