The science behind freeze response

• The sympathetic system organizes the involuntary responses that anticipate maximal exertion (in the extreme, the so-called "fight-or-flight" reaction).

• Conversely, the parasympathetic system organizes the involuntary responses that generally reflect visceral function in a state of relaxation.

When the fight or flight systems cannot be activated, escape is impossible physically or relationally and fighting is not an option for all sorts of reasons, or the traumatic threat is prolonged, the limbic system can simultaneously activate the parasympathetic branch of the autonomic nervous system, causing a state of freezing called 'tonic immobility'- like a mouse going dead when caught by a cat, or like a deer caught in headlights.

Arousal is mediated by the limbic system, which is located in the centre of the brain. This part of the brain regulates survival behaviours and emotional expression. It also influences memory processing. The limbic system has an intimate relationship with the autonomic nervous system (ANS). It evaluates a situation, signalling the ANS either to have the body rest or to prepare it for effort. (The ANS has 2 branches: the sympathetic branch which is primarily aroused in states of effort and stress, and the parasympathetic branch which is primarily aroused in states of rest and relaxation).

The nervous system responses of fight, flight and freeze are automatic survival actions. They are similar to reflexes in that they are instantaneous, but the mechanisms underlying these responses are much more complex. If the limbic system perceives that there is neither time nor strength for fight or flight, and death could be imminent, then the body will freeze.

In this state the victim of trauma enters an altered reality. Time slows down and there is no fear or pain. In this state, if harm or death do occur, the pain is not felt as intensely. People who have fallen from great heights or been mauled by animals and survived, report just such a reaction. This freeze response can increase chances of survival if the attacker (animal or human) thinks the person is dead.