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Nov 24 2015

Immobility, The Freeze Response to Trauma – The Story of the Deer in the Road

It’s Story Time!

“The Deer in the Road”

Once upon a time a deer wandered out of the forest and onto a flat, stone-like piece of ground. It was night. A few clouds passed across the moon and the wind rustled the tufts of grass along the edge of the gravely surface. All was quiet and peaceful.

A deer steps into the road at night.Suddenly a bright light filled the whole world. The light was blinding; the deer couldn’t see anything except for the piercing light. A massive, screeching angry monster was fast upon her. There was a frightful wind all around; the wind impacted her like a sudden wall of pressure pushing her back. The monster made terribly loud crunching sounds. Screaming and rumbling and roaring, it flung pieces of small rock all around with its feet. It seemed like it was all around her, everywhere at once.

A car almost hits a deerAnd then just as suddenly as it came, the monster left with a whish and a diminishing roar and it was quiet again. But she was all abuzz inside with the commotion and fear and shock. She felt as if she had been transported away from the scene, and was suspended, protected in a kind of timeless twilight zone. She was completely still.

The deer was in a state of immobility.

Even though she was completely motionless externally, it was like she had an engine running at full blast internally (a stressed state of muscle tension and elevated heart rate). As illustrated below, the engine was running but at the same time the brakes were on and the deer could not move.

A deer stands with an engine running full blast inside and car brakes being applied by feet outside her bodyDeputy Ryan Swartz arrived on the scene to find the deer standing stock still in the middle of the road. At first he thought it was a decoy, the deer was so still, but when he walked up to her he realized it was a real live deer. Even when the officer was right next to the deer and touched her back, she stayed completely still.

A police officer stands next to a deer in the middle fo the road at nightOfficer Swartz knew he had to get the deer out of the road, because she could be hit by a car if she remained standing in the road like that. Officer Swartz had to do something, but he couldn’t get her to move on her own by patting or prodding her. She was stuck there just like people who get turned to stone in fairytales. So, all out of options, he picked up the deer and carried her to the side of the road. The only alternative would have been to euthanize her for public safety.

The police officer carries the deer into the forestAfter Deputy Swartz set the deer down on the side of the road, she remained in immobility. After watching her stand there for a while, the officer pushed the deer and she finally regained her senses and ran away.

Most likely when she found herself in a safe place, and was sure there were no threatening monsters anywhere, her body shook or shivered a bit to let go of the energy of the harrowing experience. She would have released the tension, the fear, the shock, the commotion, and the activation of all physiological systems that had been bound up in readiness to fight or flee the threat, thereby returning to the state of “calm alert.” When fully back to herself, she continued with her nightly routine.

A deer shakes in the middle of a beautiful forest clearingIt was reported that the deer was in immobility for about 25 minutes before being rescued. Can you imagine being unable to move for 25 minutes? That’s a long time of being turned into a statue.

This story is an embellishment of a real event that occurred on 11/11/11 on Hellems Road in Dwight Township in Michigan. (source) Click here to watch the video.

A deer's face looking out of some green bushes

The deer is safe again and continues with her nightly routine.

All About Immobility

prey animal

Prey animals have to always be alert for predators

Because much of our physiology as humans is the same as animals — it is said our DNA is 97% identical to the chimpanzee — it is helpful to take a look at how animals handle trauma in order to understand ourselves.

Over millennia of evolution, all animals have adapted ways of dealing with trauma. Prey animals have especially had to adapt to handling life-threatening encounters, being regularly stalked, chased, and attacked by predators. While many animals have adapted ways of fighting or fleeing, some animals also freeze when confronted by a predator. This is called “tonic immobility” or just “immobility.”

Tonic Immobility

Tonic immobility (also: animal hypnosis, cataleptic immobility, paroxysmal inhibition) is defined as, “an unlearned, reversible, coma-like stasis displayed by a large number of taxa (Gallup, 1974).” (1)

The word “tonic” in this context means, “of, relating to, characterized by, or affecting normal muscular or bodily tone“ and “pertaining to tension, as of the muscles.” (source)

The animal remains in this state either for a certain duration or until something snaps it out of it like a loud noise or a touch or other change in the environment. Lemon sharks, just to give one example of the duration of immobility, stay in immobility for 15 minutes on average and some have remained unable to move for a few hours. (1)

During this state of paralysis, different kinds of animals display different physiological responses. Some show signs of elevated stress, some show signs of subdued stress, some show both simultaneously and some change during the time they are in immobility.

Here are some examples of physiological effects researchers have measured when trying to understand immobility:

  • sympathetic nervous activity (fight-or-flight response) indicators – heart rate, peripheral vasodilation (expansion of blood vessels, except for those in the core of the body, leading to decrease in blood pressure), blood pressure
  • EEG arousal (electrical activity of the brain)
  • temperature – leg (something on the periphery of the body) and core
  • muscle tone (tense versus limp)
  • breathing rate (speed) and other qualities of breathing like deep versus shallow, regular versus erratic
  • blood chemistry – acidosis (increase in acid Ph), blood sugar aka blood glucose, electrolytes, plasma potassium sodium and calcium, carbon dioxide, lactate, bicarbonate, chloride, urea

Increased Stress Markers

Terrestrial vertebrates like chickens and rabbits have shown signs of increased stress including increased heart rate, faster breathing, and tension of the skeletal muscles (the muscles we are able to control, such as arm and leg muscles). For example, “In a 2006 study concluded that rabbits show symptoms that are in line with being stressed after being in a tonic immobility state, such as a faster heart rate and breathing.” (source) One researcher states, “TI [tonic immobility] … in terrestrial vertebrates, is caused by muscle rigidity and unresponsiveness to painful stimulation (Marx et al., 2008; Ratner, 1967).” (1) The inability to feel any pain that animals experience while in immobility is called “analgesia.”

An Increase Followed Immediately by a Decrease in Stress Markers

Sometimes, the stress responses elevated initially but then reduced. In a study of hens, they found that, “The induction of TI was associated with EEG arousal [increased electrical activity of the brain], low shank temperature [shank is the part of the chickens leg between the toes and the first (knee) joint] and elevated heart rate. However, shortly after the adoption of TI, the EEG showed a predominantly slow-wave deactivated pattern, muscle tone fell and sympathetic nervous activity was reduced, as indicated by declining heart rate and peripheral vasodilation [expanding of blood vessels except those in the core of the body, lowering blood pressure].”

(source)

Simultaneously Increased and Decreased Stress Markers

Sharks respond differently than terrestrial invertebrates; they relax and breathe deeply but this does not mean they are not also experiencing stress. One researcher mentions that, “…in contrast to their terrestrial counterparts, sharks exhibit relaxed muscle tone (the “limp” response; Whitman et al., 1986). In addition, for species with the ability to self ventilate via buccal pumping [breathe by pulling water into their mouth and through their gills using their cheek muscles as opposed to swimming and letting the force of the current propel the water through their gills], individuals in TI exhibit deep rhythmical ventilations [“ventilations” means breathing] (Watsky and Gruber, 1990).”(1)

This study concluded that despite the fact that it appears the sharks are just floating around deeply relaxed, with relaxed muscles and deep regular breathing, like they’re in the spa, they are actually stressed. The study discovered that other physiological changes, such as blood chemistry changes, indicate the overall experience is stressful, concluding that “The results suggest that TI is an inherently stressful experience, which magnifies the degree of perturbation observed in a number of blood chemistry parameters.” (1)

Thanatosis – Playing Dead

There is another, similar, response to threat called “thanatosis”. Thanatosis is defined as, “In animal behavior, thanatosis is the process by which an animal feigns death in order to evade unwelcome attention.” (source) Thanatosis goes a step beyond simply being unable to move and remaining still. These animals will assume the physical position they would if they were dead (e.g. with mouth open and tongue hanging out) and sometimes emit an odor of death to completely trick any predator into believing they are dead. Two examples are the Virginia opossum and the hog-nosed snake.

opossum

opossums

Some Predators Only See Motion and Some Avoid Dead Animals

Tonic immobility can protect an animal from harm by making it blend seamlessly into the surroundings rendering it invisible, especially to predators that notice motion primarily. Immobility also makes the animal appear to be dead, in which case the predator avoids it because it could be rotten, toxic, unappetizing or infected with disease.

Many animals are reported to exhibit this behavior.

Some examples are: various species of sharks, snakes, stingrays, anole lizards, rodents, rabbits, birds (chickens are one example), invertebrates (for example a species of wasp). Scientists have induced immobility for research purposes in mice, gerbils, guinea pigs, rats, rabbits and pigs.

mouse

The Cascade
To break this process down step by step, the prey animal begins in a state of “calm alert.” This means it is calm and going about its business, its muscles are relaxed, it is breathing is normal, but it is ready to respond at the moment any danger arises. Part of its mind is alert, paying attention.

When a predator starts to chase after it, the prey animal many times will go through this sequence, although there are variations based on what various animals have evolved to do in the situation:

Initial Freeze – Voluntary Stillness: The animal may become completely still as a means to hide from the predator. If detected, they will choose to fight or flee. This has some of the same advantages of immobility but it is not the same as tonic immobility because the animal is aware and able to move at will.

Fight: The animal uses its legs (kicking), teeth, claws to try to subdue or chase away the predator.

Flee: The animal uses its legs to run, jump, or climb to safety.

In both these scenarios, the animal mobilizes as much energy as possible into its muscles to move them as fast as possible.

When the animal reaches safety, it returns to a state of calm alert.

If cornered or caught, certain animals have evolved to go into tonic immobility.

Freeze – Tonic Immobility Upon Being Caught: If the animal is overcome by the predator, in some cases it enters immobility and appears frozen, completely motionless, like a statue.

“In general, TI is thought to be the final stage of a ‘defensive cascade’ of behaviours initiated in response to the presence of a predator (Ratner, 1967). This cascade, which begins with a period of voluntary immobility intended to decrease the probability of detection and heighten responsiveness, then transitions through the ‘flight or fight’ response, and if escape is unsuccessful resulting in capture and restraint (i.e. by a predator), terminates with the onset of TI (Marx et al., 2008)” (1)

If some time passes and the predator leaves and the animal registers that the coast is clear, the animal may suddenly snap out of it and run away to a safe area. In an instant it can go from being completely paralyzed to moving at the speed of lighting. Where did all that energy come from to propel it like a race car away from the threat?

When an animal enters the freeze or immobility response, one theory is that the energy that is mobilized to be used for physical exertion somehow gets held within their body in certain ways – such as being held in the muscles. The animal looks dead, but actually it could be filled with all the energy that is needed for fleeing to use when it registers that the coast is clear. This could possibly be the case with animals that show elevated stress during immobility, such as muscle tension, increased heart rate and increased breathing, and who also exhibit a capacity to spring into action when they come to.

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Immobility helps animals remain safe from predation. Blending seamlessly into the environment is the first defense, rendering them invisible to predators who detect motion to locate prey. Some animals go even further and act dead (thanatosis) which deters predators who avoid dead prey. If caught, immobility can trick the predator into thinking their prey is already dead. The predator may stop inflicting damage on the prey earlier than they would otherwise. Also, in a moment of inattention or distraction on the part of the predator, they may stop holding or guarding their “dead” prey and the animal can make its escape.

Also, when the animal is safe again, in some instances it shakes – it’s whole body trembles or shivers for a little while. This could represent a dissipation of all that energy and tension that was stored in the muscles. Afterwards, the animal returns to the calm alert state.

Another possibility that came to my mind is that immobility could protect the psyche of the animal from experiencing the trauma of being injured or killed. If an animal is to become food for a member of the animal kingdom higher on the food chain, perhaps nature created a way to use their body to protect – to insulate or distance – their mind from directly experiencing the moment of being ripped apart and eaten. That’s total speculation on my part, but immobility could be a way of easing the traumatic impact of the experience of being captured and maimed.

Perhaps immobility protects animals before detection, after being captured, and as they are being harmed or killed. Maybe it’s this multipurpose nature that gives immobility a mix of increased and subdued stress, and variations from one animal species to the next.

References:

  1. The stress physiology of extended duration tonic immobility in the juvenile lemon shark, Negaprion brevirostris (Poey 1868) (slideshare) (video)

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I will be writing more about immobility. In future posts I will take a look at what theories exist about immobility as it occurs in human beings during traumatic experiences, and I will share an immobility healing exercise. Stay tuned. Thank you for reading and I wish you the very, very best on your healing journey.

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Heidi Hanson is an artist and writer in Asheville, North Carolina currently working on an illustrated book chronicling her journey healing from Post Traumatic Stress Disorder.

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