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Tonic Immobility as an Evolved Predator Defense: Implications for Sexual Assault Survivors


Address correspondence to Brian P. Marx, Behavioral Science Division, National Center for PTSD, VA Boston Healthcare System (116B-2), 150 South Huntington Avenue, Boston, MA 02130. E-mail:


This article reviews research concerning the possible relationship between tonic immobility (TI) and human reactions to sexual assault. This review includes a description of the characteristic features of TI and a discussion of the most widely accepted theoretical explanation for TI. The possibility that humans may exhibit TI is explored and conditions that might elicit TI in humans are identified. In particular, we focus on TI in the context of sexual assault, because this form of trauma often involves elements that are necessary for the induction of TI in nonhuman animals, namely, fear and perceived physical restraint. The important similarities and differences in how TI manifests in humans and nonhuman animals are highlighted, future research directions are offered, and clinical implications are suggested.