Freezing behavior

Freezing behavior or the Freeze Response is a reaction to specific stimuli, most commonly observed in prey animals. When a prey animal has been caught and completely overcome by the predator, it may still be possible for the prey to escape by feigning death so that the predator stops the attack. Studies typically assess a conditioned freezing behavior response to stimuli that typically or innately do not cause fear, such as a tone or shock. 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. However, since it is difficult to measure these sympathetic responses to fear stimuli, studies are typically confined to simple crouching times. A response to stimuli typically is said to be a "fight or flight", but is more completely described as "fight, flight, or freeze." In addition, freezing is observed to occur before or after a fight or flight response.

Studies suggest that specific areas of the brain are known to either elicit (or inhibit in the case of lesions) freezing behavior in subjects. The regions include the basolateral amygdala and the hippocampus.

One such study, conducted by Ann E. Power et al., investigated the effects of lesions in the basolateral amygdala. Rats were placed in a chamber containing either real cat hair or fake cat hair. Two groups of rats were tested: rats that had been lesioned in the basolateral amygdala and rats that were the control group (or sham-operated group). All rats at first froze briefly then retreated away from the stimulus upon initial contact. The results showed that the rats that were lesioned in the basolateral amygdala froze much less to the cat hair than the control group of rats. As expected, both groups of rats froze for a significantly less time when presented with the fake cat hair stimulus than when in the presence of the real cat hair. It was also shown that the both control group and the lesioned group made less contacts with the real cat hair than the fake cat hair. These data infer a connection between the basolateral amygdala and freezing behavior.

Another study, conducted by Gisquet-Verrier et al., tested the effects of the hippocampus, in three experiments, on both the freezing behavior and avoidance. The rats were lesioned with ibotenic acid, and were tested against a control group. 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. Finally, they tested conditioning with a larger stimulus (footshock intensity). It was found that avoidance was unaltered while freezing behavior decreased. Not only did these investigations show that the hippocampus is involved with freezing behavior, but avoidance and freezing behavior do not seem to have similar ways of being quantified when it comes to fear conditioning.

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