Reconceptualizing human fear memory through the defense cascade.

Human fear memory and its associated pathologies are predominantly studied within fear conditioning frameworks. While this reductionist approach has provided valuable insights into the neural and behavioral mechanisms of fear memory, it inadequately captures the diverse dysfunctions in defense responses observed in post-traumatic disorders. These dysfunctions include maladaptive immobility and aberrant fight-or-flight reactions, contributing to substantial individual variability. Traditional paradigms in human studies typically present conditioned stimuli without accounting for the imminence or spatio-temporal proximity of the threat and rely on univariate physiological measures like skin conductance to quantify magnitudes of conditioned responses. Such methods fail to encompass the full range of qualitatively distinct defense behaviors. In contrast, models on defense mechanisms highlight the cascade of defense responses across the threat imminence continuum. This review explores emerging theoretical and methodological innovations that integrate these models to extend the fear memory framework in humans. Key advancements include the dynamic manipulation of threat imminence and the integration of whole-body movements to elicit and evaluate a wider spectrum of defense modes. These innovations offer a promising path for understanding how traumatic experiences disrupt the defense system and contribute to the development of heterogeneous pathological outcomes.