Tonic immobility (freezing) during sexual and physical assaults produces stronger memory effects than other characteristics of the assaults

ABSTRACT

Tonic immobility (TI) is a phylogenetically conserved, passive, obligatory defense mechanism commonly engaged during sexual and physical assaults. During TI, people become immobile while remaining conscious and later reexperience intrusive memories of both their assault and of its accompanying immobility. Here we show that this well-studied biological process has powerful effects on memory and other processes. Participants had experienced either a serious sexual (n = 234) or physical (n = 137) assault. For both the assault and its accompanying immobility, the standard measure of the peritraumatic severity of TI correlated between .40 and .65 with post-assault effects on memory, including memory of the assault and memory of the immobility, the two memory-based self-concept measures of self-blame and event centrality, and post-assault anxiety and depression. The correlations with TI were much higher than other peritraumatic characteristics commonly used to predict and describe posttraumatic effects in assaults and other traumas. The results suggest that TI should be considered for a broader, more biologically based and ecologically valid understanding of the effects of trauma on memory and memory-based reactions.

KEYWORDS:

• Memory
• autobiographical memory
• tonic immobility
• sexual assault
• trauma

Acknowledgements

We wish to thank Dorthe Berntsen, Emilie Cieslak, Rick H. Hoyle, Yanyan Shan, Timothy Strauman, Angie Vieth, and Nancy Zucker for comments on the manuscript, Daniel Munksholm Møller and Sinué Salgado for administering CloudResearch.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Both authors contributed to the study conception, design, material preparation, writing, and editing. Carolyn F. Bell did the Qualtrics code and David C. Rubin did the statistical analysis. Both authors read and approved the final manuscript.

Ethics approval

The study was approved by the Duke University Campus Institutional Review Board.

Data availability statements

Data are available from the first author.

Additional information

Funding

This research was supported by the Charles Lafitte Foundation Program in Psychological Research at Duke University.