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Is there a canine equivalent to the highly sensitive person (HSP)?

This term, highly sensitive person, was first coined by psychologist Dr Elaine Aron and is now called high sensory-processing sensitivity (SPS) in research circles. Since reading her book The Highly Sensitive Person, and answering an emphatic “yes!” to pretty much every question on her self-assessment test (a short version is available here), I’ve assumed that this phenomenon occurs in animals as well.

(Every time I read something to do with humans, I automatically wonder whether it’s applicable to animals. One might politely call it an occupational tic; the truth is that I’m more interested in animals than in people :-)

When I read that 15–20% of the human population is considered to be highly sensitive, a roughly equal proportion to have very low sensitivity, and the majority to lie somewhere in between, I immediately thought that this breakdown probably holds true for animals as well. The research in many different species, from insects to fish to primates, has at least identified animals at both ends of the sensitivity spectrum (high or low sensitivity; "timid/shy" or "bold"; "uptight" or "laid back").

I would add that, in my experience, some species (e.g., horses) are inherently more sensitive than other species; some breeds within a species (e.g., Arabian horses) are inherently more sensitive than other breeds; some family lines (here I won’t name names) within a breed are inherently more sensitive than others; and some individuals within those family lines are inherently more sensitive than others. But I digress…

So, is there such a thing as the highly sensitive dog (HSD)? If so, what might that look like? What behavioural traits might these dogs share or exhibit more than other dogs that we could recognise as group characteristics?

When I read Dr Aron’s checklist for parents of highly sensitive children, I was struck by how very well it translates to some dogs I’ve known, and especially to one I lived with for 15 years who was very sensitive to loud noises such as thunder, fireworks, and gunshots until she developed hearing loss in old age. (We’ll circle back to this particular profile in a minute.)

That’s all well and good, but such checklists are quite subjective. Is there any objective evidence for the existence of the 'HSD' or for any specific behaviours we might consider characteristic of such dogs?

Yes, there is.

Researchers in the Department of Veterinary Biosciences at the University of Helsinki, Finland, recently published a study which identified a likely genetic basis for two specific types of anxiety in dogs: noise sensitivity and fearfulness toward strange people or situations.

Here is a link to the paper, which was published in the journal Translational Psychiatry because of its implications for similar “neuropsychiatric disorders” in people. Their words, not mine. The human research on HSP or SPS indicates that while HSPs may suffer more from anxiety in this culture that overemphasises the value of the highly insensitive individual, anxiety is not a characteristic of the HSP. Furthermore, high sensory-processing sensitivity is not considered a neuropsychiatric disorder, but rather a behavioural trait shared by a small but significant proportion of the population.

The Study

In brief, the researchers took blood samples from 330 German Shepherd Dogs (GSDs) and used a canine whole-genome tool to look for specific genetic differences among the following groups, as identified by owner responses to a behavioural questionnaire:

1. Noise Sensitivity (NS) group — dogs who are reactive to loud noises (thunder, fireworks, gunshots); 91 dogs

Reaction to loud noises included one or more of the following: salivation, defaecation, urination, destroying, escaping, panting, hiding, trembling, vocalising, freezing, holding the tail low or between the hind legs, and/or getting excited and barking when hearing thunder, fireworks, or gunshots.

2. Fear Reaction (FR) group — dogs who react fearfully toward strangers or new situations; 80 dogs

Reaction to strange people included one or more of the following: withdrawal, barking or growling (with or without going toward the person), not willing to make contact, staying close to the owner (but not under any command), holding the tail low or between the hind legs, and/or some other behaviour identified by the owner as specific to this situation.

Reaction to new situations or environments included one or more of the following: wanting out of the situation/environment, barking, panting, trembling, holding the tail low or between the hind legs, staying still and not wanting to explore the environment, staying close to the owner (but not under any command), walking low, and/or some other behaviour identified by the owner as specific to this situation.

3. ‘Control’ group — normal dogs, those who are not noise sensitive (NS Control; 210 dogs) or fearful (FR Control; 193 dogs, 180 of whom were also used for the NS Control group)

It’s worth pointing out that there was some overlap between the NS and FR groups. Of the 91 dogs in the NS group, 34 dogs (37%) were also fearful. Looking at this from the other direction, 34 of the 80 dogs in the FR group (42.5%) were also noise sensitive. So, as a broad brushstroke, about 40% of the dogs in either group were both noise sensitive and fearful toward strangers or new situations.

That’s a substantial proportion of these ‘reactive’ dogs (about 4 in 10), and hopefully it’s of some comfort to those whose dogs have more generalised anxiety: you’re not alone! It might also be a bit of a relief for those with noise sensitive or fearful dogs, that things could be worse: some dogs are both.

All 330 dogs lived in Finland, all were at least 1 year old, and all were privately owned (i.e., they were not purpose-bred research dogs). Most dogs were from either working or show lines (a point I want to come back to later).

According to the study authors, the German Shepherd breed was chosen “for its known large variation in reacting to loud noises, strangers and novel situations (shyness–boldness personality).” I take this to mean that they felt the German Shepherd breed was a good representation of the general dog population for this genetic comparison study, as it would be easy to find individuals at both ends of the shyness–boldness spectrum within the same breed.

Whether their findings are applicable to other breeds and to mixed-breed dogs remains to be seen, but it is likely to be the case — particularly in light of the fact that the authors made repeated references to similar findings in humans and to the usefulness of canine models for the study of human neuropsychiatric disorders. In other words, the authors were assuming that inferences could be made about humans, so it’s not a stretch to assume that the same conclusions may be applied to the general dog population.

This study was focused on mapping noise sensitivity and fearfulness in dogs to specific chromosomes, and to specific regions (loci, or locuses) within the chromosome that have been associated with anxiety and other neuropsychiatric disorders in people.

Noise sensitivity

They mapped noise sensitivity to canine chromosome 20 and to a locus that contains several ‘candidate’ genes associated with neuropsychiatric and hearing-related characteristics, including noise sensitivity/intolerance and age-related hearing loss. (That profile describes my dog to a T!)

For example, one of these ‘candidate’ genes is the oxytocin receptor gene. Oxytocin is a hormone that, together with its receptor, is involved in maternal bonding, other types of social bonding, and related stress behaviours.

In dogs, this receptor is involved in human-directed social behaviour such as greeting, proximity-seeking (wanting to be near us), and friendliness. (Also characteristics of my own noise-sensitive dog, who seldom met a person she didn't love at first sight.)

This study tells us nothing about the expression of this gene in noise-sensitive dogs; it simply suggests we look deeper at this particular gene and others at this locus that are associated with normal behaviour and with known neuropsychiatric disorders in people. It also suggests we look here for a genetic basis to age-related hearing loss.

Fearfulness

Perhaps not surprisingly, fearfulness toward strangers and new situations was much more complex, involving several different chromosomes (most prominently, but by no means exclusively, canine chromosome 7) and several ‘candidate’ genes, notably those involved in bipolar disorder and schizophrenia in humans.

I think that’s an unhelpful and potentially harmful line to draw between the two species, because it risks branding these fearful dogs as ‘crazy’ in the eyes of the general public or as having a ‘neuropsychiatric disorder’ (read 'medication deficiency') in professional circles.

What if these dogs are simply highly sensitive individuals — or to use the scientific term, they have high sensory-processing sensitivity?

If so, then it is probable that they are simply more easily overwhelmed by novel situations, including unfamiliar people, which is a characteristic of the HSP.

Does this high sensitivity make these dogs feel a little ‘crazy’ at times? Probably; it certainly does me (a HSP). But are they ‘crazy’ dogs? Almost certainly not.

(Not to head off down a side track, but we must leave room here for individuals with brain lesions or other medical conditions that affect brain function, such as liver disease. They are not ‘crazy’ dogs, either, but they may show very abnormal behaviour. Such dogs require proper diagnostic workups and whatever medical or surgical treatment is indicated as a result.)

So, this study provides objective evidence that there is some genetic component to these behavioural problems in German Shepherd Dogs, and this conclusion probably extends to other dogs as well. But how can this information help us better manage these dogs?

Read on...

© Christine M. King, 2019, 2022. All rights reserved.

First published on WordPress, 03 Feb 2019.

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