[1][2] When a prey animal has been caught and completely overcome by the predator, it may respond by "freezing up/petrification" or in other words by uncontrollably becoming rigid or limp.
Freezing behavior is most easily characterized by changes in blood pressure and lengths of time in crouching position, but it also is known to cause changes such as shortness of breath, increased heart rate, sweating, or choking sensation.
[3] However, since it is difficult to measure these sympathetic responses to fear stimuli, studies are typically confined to simple crouching times.
Studies suggest that specific areas of the brain are known to either elicit or inhibit (in the case of lesions) freezing behavior in subjects.
Another study, conducted by Gisquet-Verrier et al., tested the effects of the hippocampus, in three experiments, on both the freezing behavior and avoidance.
They first investigated changes from conditioned fear, and results showed that lesions to the hippocampus did not alter freezing behavior and marginally affected avoidance.
Next, they tested single conditioning sessions, and it was found that freezing behavior remained unchanged while avoidance was disrupted.
This suggests that antipsychotic drugs alter freezing behavior, making the rats more sensitive to fear stimulus, for example.
[11] Tsuchiya et al. conducted a study investigating the effect of methamphetamine pretreatment on freezing behavior.
This evidence suggests that previous exposure to chronic methamphetamine results in an increased sensitivity to subsequent stress than a control group.
The results showed that acute inhibition of both monoamine oxidase A and B reduce anxiety or freezing behavior.
The authors then administered progesterone and estrogen in ovariectomized rats and tested them in marble burying and conditioned fear.