Exploring human freeze responses to a threat stressor.

Despite the fundamental nature of tonic immobility in anxiety responses, surprisingly little empirical research has focused on the "freeze" response in humans. The present report evaluated the frequency and predictors of a freeze response in the context of a biological challenge. A nonclinical sample (N=404) underwent a 20-s inhalation of 20% CO(2)/balance O(2). Perceptions of immobility in the context of the challenge were reported in 13% of the sample, compared with 20% reporting a significant desire to flee. Subjective anxiety and panic during the challenge were associated with the freeze response, as were a number of anxiety symptom dimensions.