Tonic immobility is a natural state of paralysis which is said to occur in humans as well as animals when they are subjected to intense trauma such as rape or sexual assault. A recent research that is being published in Acta Obstetricia et Gynecologica Scandinavia, found that most of the rape victims experience a state of involuntary paralysis, called the tonic immobility. Tonic immobility is also associated with subsequent posttraumatic stress disorder (PTSD) and severe depression after rape.
The findings indicate that for health care follow-up and legal matters, tonic immobility should be assessed in all sexual assault victims.
Though, little is known about tonic immobility in humans. To investigate, Anna Moller and her colleagues from the Karolinksa Institute and the Stockholm South General Hospital in Sweden assessed tonic immobility at the time of assault in 298 women who had visited the Emergency Clinic for Rape Victims in Stockholm within one month of a sexual assault. After 6 months, 189 women were assessed for the development of PTSD and depression. Of the 298 women, 70% reported significant tonic immobility and 48% reported extreme tonic immobility during the assault. Among the 189 women who completed the 6-month assessment, 38.1% had developed PTSD and 22.2% had developed severe depression.
Tonic immobility was associated with a 2.75-times increased risk of developing PTSD and a 3.42-times increased risk of developing severe depression. Prior trauma and a history of psychiatric treatment were also linked with tonic immobility.
"The present study shows that tonic immobility is more common than earlier described. This information is useful both in legal situations and in the psychoeducation of rape victims. Further, this knowledge can be applied in the education of medical students and law students." Says Moller.
Tonic immobility is more common in animals. It is considered as an evolutionary adaptive defensive reaction to a predatory attack by the animals when resistance is not possible and other resources are not available.