A Multi-Method Investigation of Tonic Immobility and Implications for Trauma-Related Disorders

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Project Summary. Extant research on animal and human threat responding has identified adaptive ways of managing threat (i.e. fight-flight-freeze). Although freezing in response to threat may be adaptive in certain circumstances, it can also reduce chances of escape, resulting in increased physical and mental health risk. Despite its importance, research on human freeze responding is highly limited due to lack of integration across levels of analysis. While the majority of studies use retrospective self-report measures of tonic immobility (TI) that were reverse engineered from anecdotal reports of freezing in response to traumatic events such as sexual assault and combat, experimental studies of freeze response in humans evolved from animal research paradigms. Thus, examination of human immobility in response to threat currently relies on retrospective self- report or behavioral data alone, making it difficult to integrate and compare findings across studies. Additionally, though animal research suggests a link between freezing and alterations in threat processing, research has not yet begun to examine the neural basis of human immobility in response to threat. The P1 and LPP event-related potentials (ERPs), which have been reliably associated with attention to threat and threat processing, may provide insight into the nature and impact of freeze responses including TI. Taken together, the overall aim of the current proposal is to examine immobility in response to threat and its relationship with trauma related psychopathology across multiple levels of analysis, consistent with the NIMH RDoC initiative. The proposed study will 1) develop a unified index of TI utilizing a lab-based experimental threat paradigm to assess behavioral and self-report markers of immobility, 2) investigate the neural markers associated with immobility in response to threat (i.e. P1, LPP), and 3) examine the associations between prior TI exposure, lab- induced immobility, and psychopathology across individuals and groups. Adult female participants (N = 180) including individuals with prior TI, prior trauma exposure without TI, and healthy controls will complete one three-hour lab appointment after determination of initial eligibility and consent. Trained doctoral level graduate students will administer structured clinical interviews (SCID-5-RV) to determine eligibility and diagnoses. Then, participants will complete a self-report questionnaire battery followed by two experimental tasks. Previously validated image viewing and autobiographical script tasks will be used to elicit immobility responses. Behavioral (postural sway, heart rate), neurophysiological (EEG/ERP), and self-report data will be collected. The proposed study will serve to inform future research, preventative interventions, and treatment of trauma- related disorders. Another key aspect of this proposal will be in the training that the primary investigator (PI) receives. This training will provide the PI with the necessary skills to integrate neurophysiological and advanced statistical methods into future work.