The Role of Tonic Immobility in the Development of PTSD Symptoms

Abstract

Tonic immobility (TI) is a state of physical and verbal immobility to intense or painful stimulation. It is triggered by situations of fear and physical restriction or/and the incapacity to escape. The occurrence of tonic immobility tends to be a strong predictor of the severity of PTSD and treatment seems to be less effective. However, previous research on the effects of tonic immobility has included mostly retrospective studies. In this study a fear condition experiment was used to gain more knowledge of the relationship between TI and intrusions and the relationship between TI and extinction. The first hypothesis tested the relationship between TI and the number of intrusions. It was expected that participants who experience TI would have a higher intrusion frequency than those who experience less TI. The second hypotheses tested if the extend of TI affects the extinction of the UCS expectancy. It was expected that extinction takes longer when participants experience TI during the experiment. In contrast to earlier research, TI did not correlate with the number of intrusions. However, an effect from TI on the duration of extinction of the UCS expectancy was found in this study. Limitations of the present study and future directions are discussed. Future research needs to examine more closely the links between tonic immobility and PTSD.