Fear in action: Fear conditioning and alleviation through body movements

Fear memories enhance survival especially when the memories guide defensive movements to minimize harm. Accordingly, fear memories and body movements have tight relationships in animals: Fear memory acquisition results in adapting reactive defense movements, while training active defense movements reduces fear memory. However, evidence in humans is scarce because their movements are typically suppressed in experiments. Here, we tracked adult participants’ body motions while they underwent ecologically-valid fear conditioning in a 3D virtual space. First, with body motion tracking, we revealed that distinct spatiotemporal body movement patterns emerge through fear conditioning. Second, subsequent training to actively avoid threats with naturalistic defensive actions led to a long-term (24 hrs) reduction of physiological and embodied conditioned responses, while extinction or vicarious training only transiently reduced the responses. Together, our results highlight the role of body movements in human fear memory and its intervention.

Methods

We conducted experiments across three consecutive days. On day 1, 41 participants (Group 1) underwent a naturalistic threat conditioning session in an unconstrained standing posture inside a virtual elevator. On day 2, participants underwent embodied active- avoidance training (ACT training) where they could defend themselves with a security spray to prevent violence (US) from one of the CS+ avatars. On day 3, participants encountered both CS+active and CS+extinction avatars without violence and we tested for the return of threat-conditioned responses in the spontaneous recovery test session. 

To further elucidate the spatio-temporal dynamics of embodied CRs across the entire body, a second group of 54 participants (Group 2) completed the same conditioning session as Group 1 with an addition of a whole-body motion tracking system

Along with physiological defensive reactions as measured with skin conductance responses (SCR) and subjective ratings of fear and violence-likelihood, the body movements of the participants were tracked with the VR head-mount-display and hand-held controller (Group 1) or with a full-body motion system (Group2).