The role of tonic immobility and behavioural control in intrusion development

Background: Tonic immobility (TI; involuntary motor inhibition during threat) has been implicated in the onset of posttraumatic stress disorder (PTSD) in previous studies, using cross-sectional designs and (retrospectively measured) TI. Only one study examined spontaneous TI responses in a more controlled setting,using experimental trauma (a ‘trauma film’). TI during the ‘trauma film’ was indeed associated with increased frequency of intrusive memories of the film (Hagenaars & Putman, 2011). Interestingly, high attentional control(the ability to focus and switch attention) buffered against this effect. Reduced controllability was indeed proposed to stimulate PTSD development. In experiments, behavioural control was related to reduced stress when anticipating threat. However, findings are less consistent or scarce for the impact period and postthreat period. 
Objective: Replicate the TI x Controlinteraction1 (but with behavioural control) for the impact and post-threat period. 
Method: Sixty-four participants watched an experimental trauma (negative pictures) while being allowed to close their eyes or not. Spontaneous TI was measured after picture viewing; intrusions were recorded in a diary in the subsequent week. Informative hypotheses were tested with Bayesian analyses. Results: TI predicted intrusion development. Moderation (TI x Control) and non-moderation (main effect of TI only) were both adequate models, with no preference for either. 
Conclusions: We replicated earlier cross-sectional findings regarding TIusing a longitudinal trauma-analogue design. The role of behavioural control may be complicated and/or indirect