New study finds Sexual Assault May Trigger Involuntary Paralysis

“Tonic immobility” hinders the ability to fight and is linked to high rates of depression and PTSD. Tonic immobility (TI) describes a state of involuntary paralysis in which individuals cannot move or, in many cases, even speak. In animals this reaction is considered an evolutionary adaptive defense to an attack by a predator when other forms of defense are not possible. Much less is known about this phenomenon in humans, although it has been observed in soldiers in battle as well as in survivors of sexual assault.