Notes that animal hypnosis, or tonic immobility, is an easily induced and readily quantifiable phenomenon found in many different species. Recent findings on the behavioral, ecological, chemical, neurological, genetic, and ontogenetic aspects of animal hypnosis are reviewd in light of current and hi

Animal hypnosis: Factual status of a fictional concept.

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

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

This study evaluated whether tonic immobility mediates the relations between perceived inescapability, peritraumatic fear, and posttraumatic stress disorder (PTSD) symptom severity among sexual assault survivors. Female undergraduates (N = 176) completed questionnaires assessing assault history, perceived inescapability, peritraumatic fear, tonic immobility, and PTSD symptoms. Results indicated that tonic immobility fully mediated relations between perceived inescapability and overall PTSD symptom severity, as well as reexperiencing and avoidance/numbing symptom clusters. Tonic immobility also fully mediated the relation between fear and reexperiencing symptoms, and partially mediated relations between fear and overall PTSD symptom severity, and avoidance/numbing symptoms. Results suggest that tonic immobility could be one path through which trauma survivors develop PTSD symptoms. Further study of tonic immobility may inform our ability to treat trauma victims.

Tonic immobility mediates the influence of peritraumatic fear and perceived inescapability on posttraumatic stress symptom severity among sexual assault survivors.

Individual differences in tonic immobility may reflect behavioural strategies

Tonic immobility and emergence time in pigs—more evidence for behavioural strategies

Several lines of evidence suggested that genetic factors influenced immobility reflex (IR) behavior, known commonly as “animal hypnosis,” a relatively unresponsive state of reversible immobility. Genetic influence was tested by comparing the susceptibility of two well-established strains of rats (Tryon) that had been developed for “maze brightness” (TMB) and “maze dullness” (TMD). The spontaneous durations of IR in TMB rats averaged approximately double those of TMD rats, and the time required to induce the state in TMB rats was significantly shorter. Correlated with the high IR susceptibility of the TMB rats was a pronounced lack of exploration in a novel environment. As another test of the hypothesis, selective inbreeding of Wistar rats led to the development of two strains, one highly susceptible and the other relatively insusceptible in the third and fourth generations. Testing revealed statistically significant differences between the two strains in terms of average duration of IR, average induction time, the percentage of susceptibility, the percentage which met the criteria for a high degree of susceptibility, and the percentage in each strain which were insusceptible.

C. P. McGraw

Papers

Genetic differences in susceptibility of rats to the immobility reflex ("animal hypnosis").