Postural freezing foretells startle-potentiation in a human fear-conditioning paradigm

Freezing to impending threat is a core defensive response. It has been studied primarily using fear-conditioning in non-human animals, thwarting advances in translational human anxiety-research. Here we examine postural freezing as a human conditioning-index for translational anxiety-research. We show (n=28) that human freezing is highly sensitive to fear-conditioning, generalizes to ambiguous contexts, and amplifies with threat-imminence. Intriguingly, stronger parasympathetically-driven freezing under threat, but not sympathetically-mediated skin conductance, predicts subsequent startle magnitude. These results demonstrate that humans show fear-conditioned animal-like freezing responses, known to aid in active preparation for unexpected attack, and that freezing captures real-life anxiety-expression. Conditioned freezing offers a promising new, non-invasive, and continuous, readout for human fear-conditioning, paving the way for future translational studies into human fear and anxiety.