@phdthesis{Merscher2024,
  author    = {Merscher, Alma-Sophia},
  title     = {To Fear or not to Fear: Unraveling the (Oculo)motor and Autonomic Components of Defensive States in Humans},
  doi       = {10.25972/OPUS-32791},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327913},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Defensive behaviors in response to threats are key factors in maintaining mental and physical health, but their phenomenology remains poorly understood. Prior work reported an inhibition of oculomotor activity in response to avoidable threat in humans that reminded of freezing behaviors in rodents. This notion of a homology between defensive responding in rodents and humans was seconded by concomitant heart rate decrease and skin conductance increase. However, several aspects of this presumed defense state remained ambiguous. For example, it was unclear whether the observed oculomotor inhibition would 1) robustly occur during preparation for threat-avoidance irrespective of task demands, 2) reflect a threat-specific defensive state, 3) be related to an inhibition of somatomotor activity as both motion metrics have been discussed as indicators for freezing behaviors in humans, and 4) manifest in unconstrained settings. We thus embarked on a series of experiments to unravel the robustness, threat-specificity, and validity of previously observed (oculo)motor and autonomic dynamics upon avoidable threat in humans. We provided robust evidence for reduced gaze dispersion, significantly predicting the speed of subsequent motor reactions across a wide range of stimulus contexts. Along this gaze pattern, we found reductions in body movement and showed that the temporal profiles between gaze and body activity were positively related within individuals, suggesting that both metrics reflect the same construct. A simultaneous activation of the parasympathetic (i.e., heart rate deceleration) and sympathetic (i.e., increased skin conductance and pupil dilation) nervous system was present in both defensive and appetitive contexts, suggesting that these autonomic dynamics are not only sensitive to threat but reflecting a more general action-preparatory mechanism. We further gathered evidence for two previously proposed defensive states involving a decrease of (oculo)motor activity in a naturalistic, unconstrained virtual reality environment. Specifically, we observed a state consisting of a cessation of ongoing behaviors and orienting upon relatively distal, ambiguous threat (Attentive Immobility) while an entire immobilization and presumed allocation of attention to the threat stimulus became apparent upon approaching potential threat (Immobility under Attack). Taken together, we provided evidence for specific oculomotor and autonomic dynamics upon increasing levels of threat that may inspire future translational work in rodents and humans on shared mechanisms of threat processing, ultimately supporting the development of novel therapeutic approaches.},
  subject      = {Furcht},
  language  = {en}
}