Emotion Dysregulation, Mindfulness, Self-Compassion, and Values Engagement in U.S. Iraq and Afghanistan-Era Veterans.

The ability to exhibit a wide range of defensive behaviors in response to imminent danger is crucial for survival. When faced with threat, organisms adjust their responses based on the level of threat imminence, ranging from more reflexive and short-sighted actions for proximal threats to more deliberate actions that allow enhanced information processing and planning when the threat is more distal (). For instance, when faced with imminent, inevitable danger, organisms might resort to fight or flight behaviors or engage in , a late-stage defensive state characterized by profound motor inhibition and reduced behavioral flexibility, as a last defensive resort (; ; ). By contrast, when a potential threat has been detected but the situation remains ambiguous and the danger might still be avoided with appropriate responses, organisms frequently enter a state of (; ). This state is often equated with restricted mobility, so-called freezing, especially in rodents (). Because the term “freezing” has been used inconsistently to describe different immobility responses across threat contexts, we focus here on attentive immobility to clearly specify the defensive state of interest (; ). Attentive immobility describes a complex response pattern that is not limited to the motor component but is accompanied by specific autonomic changes, including fear bradycardia, and increased sympathetic arousal (). Importantly, unlike , attentive immobility represents an active, preparatory state that supports threat monitoring and action preparation, rather than a passive shutdown response occurring when defensive options are exhausted (; ). Recent research has increasingly focused on attentive immobility in humans, as aberrant patterns have been implicated in various clinical conditions, such as PTSD () or panic disorder (), as well as in subjects with a higher number of aversive life events () and elevated levels of trait anxiety (; ). Additionally, similarities in response patterns across species, including rodents, non-human, and human primates, have been observed: In humans, similar to other species, attentive immobility is characterized by motor inhibition and concurrent sympathetic and parasympathetic upregulation (). Even though motor inhibition is much more pronounced in rodents, studies using movement tracking found decreased body sway in response to uncertain threats (; ), and motor inhibition further seems to extend to eye movements (“freezing of gaze”), as indicated by fewer and longer fixations as well as a more centralized visual exploration patterns (, ; ; ). Empirical evidence further suggests that attentive immobility in humans is associated with fear bradycardia and increased skin conductance levels (; ; ; ; ), as well as enhanced perceptual sensitivity (), and facilitated action preparation (; ). A recent study investigating electrocortical activity during states of attentive immobility found pronounced suppression of visual alpha power (), indicating heightened cortical arousal (; ) and enhanced attentional processes (; ). Faster responses to escape from threat were predicted by a more centralized gaze, stronger heart rate deceleration, and increased suppression of alpha activity, highlighting the functional significance of these components (). In summary, attentive immobility in humans has been associated with a complex multimodal pattern on the electrocortical, autonomic, and behavioral level, which is assumed to enhance perceptual processing and action preparation. These findings underscore the conceptualization of attentive immobility as an active, adaptive mechanism to cope with imminent threat (). A persistent challenge in understanding defensive responding lies in the fact that autonomic reactivity is not consistently threat specific. Measures such as heart rate deceleration, skin conductance level, pupillary responses, and body sway do not consistently distinguish between threatening, safe, or even rewarding contexts. In several task settings, these responses have instead been linked to the opportunity for action—such as quickly pressing a button or using a virtual gun to counter a potential opponent—suggesting that autonomic activity may reflect action readiness alongside, or independent of, threat processing (; ; ). On the one hand, these findings may suggest an intrinsic link between action preparation and threat-related processes (). On the other hand, they might also reflect specific features of experimental paradigms focused on contrasting active and passive threat conditions (e.g., ; ). While comparisons between high- and low-threat conditions within active paradigms have shown that heart rate dynamics are potentiated by threat of shock (; ), it remains unclear whether and how autonomic and neural markers are differentially affected by threat intensity and action possibility when these factors are manipulated orthogonally.