Immobility reactions under threat: A contribution to human defensive cascade and PTSD

Incident experience predicts freezing-like responses in firefighters

Freezing is a defensive response to acute stress that is associated with coping and alterations in attentional processing. However, it remains unclear whether individuals in high risk professions, who are skilled at making rapid decisions in emergency situations, show altered threat-induced freezing. Here we investigated the effect of incident experience in a high risk profession on freezing. Additionally, we explored whether any effect of incident experience on freezing would be different for profession-related and -unrelated threat. Forty experienced and inexperienced firefighters were presented neutral, pleasant, related-unpleasant, and unrelated-unpleasant pictures in a passive viewing task. Postural sway and heart rate were assessed to determine freezing. Both postural and heart rate data evidenced reduced freezing upon unpleasant pictures in the experienced versus the inexperienced group. Relatedness of the unpleasant pictures did not modulate these effects. These findings indicate that higher incident experience relates to decreased threat-induced freezing, at least in a passive task context. This might suggest that primary defense responses are malleable through experience. Finally, these findings demonstrate the potential of using animal to human translational approaches to investigate defensive behaviors in relation to incident experience in high risk professions and stimulate future research on the role of freezing in resilience and coping.

Sexual trauma is more strongly associated with tonic immobility than other types of trauma - A population based study

BACKGROUND

Tonic immobility is an involuntary motor and vocal inhibition reaction, considered the last-ditch response of the defensive cascade model. It is elicited in context of inescapable threat and perception of entrapment. Our aim was to investigate the association between different traumatic events and peritraumatic tonic immobility (PTI) in a representative sample of the general population.

METHODS

This is a cross-sectional study of general population from Rio de Janeiro and São Paulo with 3231 victims of traumatic events aged 15-75 years who completed the Tonic Immobility Scale (TIS). We calculated the frequency of the different traumatic events and estimated the mean scores with 95% confidence intervals for each traumatic event, controlling for the potential confounders using multiple linear regression models. Finally, we calculated the proportion of individual scoring zero in TIS for the 16 traumatic events.

RESULTS

PTI scores in child sexual abuse and adult sexual violence were almost twice as high as in other types of traumatic events, even when controlled for gender and educational level. Torture and war also showed high PTI scores, but these were based on very small number of cases and need to be interpreted with caution. Furthermore, victims of sexual trauma had the lowest proportion of individuals with total absence of PTI symptoms.

LIMITATIONS

This is a cross-sectional study and causal inferences must be drawn with caution.

CONCLUSIONS

Peritraumatic tonic immobility is more strongly associated with sexual trauma, particularly in childhood, than to other types of trauma in the general population.