Is there tonic immobility in humans? Biological evidence from victims of traumatic stress

Abstract

Tonic immobility, characterized by profound motor inhibition, is elicited under inescapable threat in many species. To fully support the existence of tonic immobility in humans, our aim was to elicit this reaction in a laboratory setting and measure it objectively. To mimic exposure to life-threatening events in the lab, trauma-exposed participants with PTSD (n=18) and without PTSD (n=15) listened to the script of their autobiographical trauma. Posturography and electrocardiography were employed. Reports of script-induced immobility were associated with restricted area of body sway and were correlated with accelerated heart rate and diminished heart rate variability, implying that tonic immobility is preserved in humans as an involuntary defensive strategy. Immobility reports seemed more evident in PTSD, suggesting that, in some patients, tonic immobility may be elicited during re-experiencing episodes in daily life. This study provided a measure of tonic immobility, a peritraumatic reaction for which cumulative clinical evidence had linked to the severity of PTSD.

Predictores de la inmovilidad tónica ante eventos traumáticos

“…Second, and aside from the retrospective bias, it is unclear to what extent self-report questionnaires can truly capture the degree of TI experienced, which may be more accurately measured through interviews or, even better, through direct observation after the event; indeed, a significant number of false positive reports cannot be ruled out (Zoellner, 2008). It is worth noting, however, that in a study which used a measure similar to the TIS-BM, Volchan et al (2011) found an association between retrospective self-reports of TI during a traumatic event and restricted area of body sway when participants listened to a script of their traumatic experience. A third limitation of our study is that the results are based on the worst traumatic event experienced and this may not be representative of other events of the same type; for instance, the worst traffic accident a person experiences might not be representative of other motor vehicle accidents (Breslau et al, 1998;Frazier et al, 2009).…”

Autonomic Dysfunction in Catatonia in Autism: Implications of a Vagal Theory

“…Tonic immobility is a last-ditch animal defense strategy against entrapment by a predator within a sequence of freezing-flight-fighttonic immobility. Volchan et al [63] found signs of tonic immobility, such as reduced body sway, increased heart rate, and diminished heart rate variability, in trauma-exposed patients with PTSD while listening to their autobiographical trauma, implying that tonic immobility is preserved in humans as an involuntary defensive strategy.…”

Catatonia: The Ultimate yet Treatable Motor Reaction to Fear in Autism

“…Further human study of the immobilization response [70,76] and Polyvagal Theory [73] promises to increase our understanding of the role of trauma in catatonia, to clarify the evolution-based effects of perceived danger on the relation between visceral states and social engagement and disengagement, and to elucidate the mechanism whereby extreme fear by perceived danger can induce such profound and perilous reaction like catatonia often requiring the use of benzodiazepines or ECT for safe reversal [77].…”