The current study is the first known research to investigate the association of the freezing response with PTSD and traumatic stress in the military veteran student population. Current understanding of the freezing response are primarily based in comparative psychology, with some studies extending to human participants (Azevedo et al., 2005; Facchinetti et al., 2006; Hagenaars et al., 2012; Volchan et al., 2017). Models generally agree that the freezing response consists of reduced body sway with decreased heart rate (Porges, 2003, 2007; Hagenaars et al., 2014).
Thirty-eight military veteran students (n=38; 18 female; 20 male) with ages ranged from 19 to 49 participated in the study. Participants completed self-report assessments administered through Qualtrics, which include the PTSD Checklist (PCL-5; Weathers et al., 2013), Brief Trauma Questionnaire (BTQ; Schnurr et al., 1999), and additional demographic, health, and military questions. To objectively measure the freezing response, participants stood on a stabilometric platform (Tekscan Inc., South Boston, MA) with a heart rate variability (HRV) monitor attached. Participants then completed four 60-second trials. The first trial was a baseline with eyes open, followed by three trials of randomized emotional stimuli of neutral, pleasant, and unpleasant images from the International Affective Picture System (IAPS; Lang et al., 1997).
Results reveal evidence of a freezing response that includes reduced body sway and bradycardia when veteran students are presented with imminent threat in the form of unpleasant stimulus. Participants with severe PTSD symptomology and a history of traumatic events measured a freezing response across all emotional stimuli except the unpleasant stimulus where they had an avoidant response. This may indicate the cumulative effect of traumatic life events on the defense system. This study contributes to the body of knowledge on the freezing response in humans that indicates an increased risk for the development of PTSD and increased severity of symptoms.
Keywords: PTSD, traumatic life events, military veterans, university students, stress response, fear response, freezing, avoidance, tonic immobility, body sway, heart rate, posturography, stabilometer, stress, traum
