A recent article was encouraging owners to hypnotise their pets, by putting them into a state called ‘tonic immobility’. This state is best described as motor inhibition in response to restraint.
The article read:
What will a hypnotised dog’s body language be like? You’re waiting to see a state known as tonic immobility. They’ll be perfectly still and limp. At this point, you should be able to release them, and they’ll remain in a tonic state.
Although the animal may remain perfectly still, as if relaxed and hypnotised, it may not be as calming as you expect. Let us investigate the evidence to decide if this is really something we should be encouraging owners to partake in.
Table of contents
Tonic Immobility
Tonic immobility is a phylogenetically (evolutionarily) old defence response that occurs in a large number of species; insects, crustaceans, fish, amphibians, reptiles, birds, and mammals, including primates and humans.
‘Tonic immobility’ or ‘animal hypnosis’, can also be known as ‘fright paralysis’, owing to the theory that animals will enter this state in times of extreme stress such as during predation, this may be known as hypnotic analgesia, or a state where the animal is less responsive or aware of painful stimuli.
Tonic immobility is usually a terminal defence used when flight or fight has failed, and the animal has been caught by a predator. Its function is to deactivate the predator’s killing reflex or to discourage consumption, as many predators are reluctant to eat dead meat.
We can investigate this by looking at research into prey species such as rabbits
Hypnotised rabbits exhibit miosis (constriction of the pupil), analgesia (pain relieving effects). Some note increased depth of respiration, and reduced respiratory rate, heart rate, and blood pressure, while others found significant elevations in respiration, heart rate and plasma corticosterone were observed following Tonic Immobility.
The conclusion was drawn that both the physiological and behavioural responses of rabbits to Tonic Immobility are indicative of a fear motivated stress state. So, in rabbits it is thought to be a stress related response, is this the same as our predatory animals such as canines; or do they also exhibit this behaviour due to a fear response?
Dogs
In an initial survey, 132 dogs were tested twice for tonic immobility. Once by inversion and 30s restraint in the lateral position and once with an additional treatment (stroking, scruffing, blanket over head, cuff around ears or light into eyes) during the 30s restraint. Based on the criterion of remaining in the position restrained, without lifting its head off the test surface, for a minimum of 10s after release from restraint. Interestingly only 10 of the 132 dogs (7.6%) exhibited tonic immobility.
In a (very small) study of nervous dogs, it was found that 10 of 10 nervous dogs, in contrast to kennel mates of a normal line, developed tonic immobility induced by manual inversion into a sling and stroking.
Humans
The defence cascade in humans involves the following action patterns or mind-body states including arousal, the first step in activating the defence cascade; flight or fight, an active defence response for dealing with threat; freezing, which is a flight-or-fight response put on hold; tonic immobility, a response to inescapable threat, or a strategy of last resort, when active defence responses have failed; collapsed immobility, a variant of tonic immobility, in which muscle tone is lost and consciousness is compromised secondary to bradycardia-induced cerebral hypoxia; and quiescent immobility, a state of quiescence that promotes rest and healing.
Although humans are not often in the position of being a ‘prey species’, there are dangers or threatening situations where they may enter this tonic immobility or ‘hypnotic’ status due to fear. As the literature says, tonic immobility in humans is often a response to inescapable threat; or a strategy of last resort, when active defence responses have failed.
Conclusion
I see very little reason that we need to be ‘hypnotising’ our pets. Evidence does not yet give us enough confidence that it is calming, or stress free. In fact, evidence is suggestive that this actually comes off the back of a pathological fear response. Although it is noted that it may be useful to conduct very short and non-painful procedures, I do not think this will be something the majority of professionals will ever engage in. And therefore there is also little need for owners to try to attempt it either.
Discussion