Dogs vs Cats: the Human-Pet Relationship
It's nearly Christmas! Grab a mince pie and get comfy as this month Naked Neuroscience navigates the relationships we have with our pets. What makes some cat noises so annoying? Why are we such suckers for a cute dog? Plus, of course, some of the latest neuroscience news from our Cambridge-based experts...
In this episode
01:23 - Disgust starts in the stomach
Disgust starts in the stomach
Duncan Astle, Cambridge University; Helen Keyes, ARU
Disgust is a rather powerful response, and not one we tend to habituate to, according to Cambridge University's Duncan Astle who this month looked at a study which found that interfering with stomach activity can influence our emotional disgust response. And this could be big news for people who suffer from pathological, extreme disgust...
Duncan - They recruited subjects and they tracked their eye movements whilst they watched images of faeces, paired with neutral stimuli like pictures of buttons or something. And what you find very reliably is that when you pair these images together, people will always choose to look away from the disgusting image and towards the neutral thing. And if you reward them for looking at the disgusting image, so you kind of pay them to look at the poo, then you find that they will do it for a reward. So they will do it for money. But as soon as you take the reward away, they very quickly return to their previous behaviour, which is to look away from the disgusting image. That's a really reliable finding.
Katie - Makes sense!
Duncan - And so what they then did was to give participants either a placebo pill or a domperidone pill. So domperidone is an anti-emetic, it's an anti-sickness drug. And when subjects were on the domperidone, this paying people to look at the poo carried over significantly more into the subsequent phase, implying that the training that you get when you're being rewarded for looking at the disgusting image, had a more long lasting effect on behaviour. By altering people's gut reaction in their stomach, to the disgusting image, you had also influenced their behavioural response to it.
Katie - So what mechanistically is domperidone changing in the stomach then?
Duncan - Well, it acts via dopamine and it's thought to influence the rhythmic muscular movements that your stomach does. And so when you see something disgusting, you get to kind of dysrhythmia, I kind of disruption of the stomach's natural rhythm, that feeling down in your gut that's not very pleasant. The medication is designed to interfere with that process. And so the idea is - which is really quite a controversial idea - is that your behavioural response to disgusting material isn't just sort of driving the physical gut response to it on its own. You can actually get the reverse. So that if you alter the physical response to the material in your stomach, then that can influence the behaviour. So the causality can run in the opposite direction to the direction you might think of it.
Katie - So what you're saying is, the turning of your stomach that you might experience when you see something disgusting and awful could actually be causing you to feel disgusted.
Duncan - Exactly.
Katie - Does this suggest that a drug that acts in this way, like domperidone, could be a way of treating people who have a really adverse, sort of over-the-top disgust response?
Duncan - So in this case, what they were able to show is that when you pair the drug with in this case, the adverse training - so paying people to look at the poo - that's when you get the effect. And so I guess, if we were to extrapolate that out to a clinical setting, it might be that what you do as a therapy is combine behavioural therapy with something - this case, you know, the anti-emetic drugs - there might be some sort of physical symptoms to treat as well as the behavioural symptoms. And that doing both things together might have some effect on these very hard-to-shift biases that people might have.
From disgust to cravings now, and social cravings to be precise. ARU perceptual psychologist Helen Keyes told Katie Haylor about a study that asked whether social isolation could provoke a response similar to being hungry - in other words, can you crave company in a similar way to craving food? And what does this social craving look like in the brain? Here’s Helen.
Helen - So to look at this, they recruited 40 participants and they recorded their brain activity in an MRI machine in three different conditions. After 10 hours of fasting, after 10 hours of social isolation - so no social stimulation, no social media, not even allowed to read a novel, just completely isolated - or in the control condition. So when the participants hadn't been deprived of food or social contact.
Now the behavioural results was measured using questionnaires on self-reported cravings. And probably not surprisingly, participants reported craving food after the fasting condition. And they reported craving social contact after the social isolation condition. But much more interesting was the findings around the neural responses. So the dopaminergic mid-brain regions were particularly of interest here. So these areas are activated traditionally by cravings for food and addictive drugs. So the researchers were particularly interested in what would happen here.
Now, when the participants were in the MRI machine, they did a task called a cue induced craving task. Essentially the participants were shown images of the things that they might be craving and their brain activity was monitored. And what I like about this experiment was they actually tailored it to each participant. So they asked participants what their favorite social activities were. They tailored those images to you specifically, and they did the same with your favourite foods, or you were just shown control images of flowers. And they found, interestingly, that responses to food cues in this dopaminergic midbrain region that is kind of associated with cravings and addiction, they found that responses to food cues were higher after the fasting condition, compared to the other conditions. And they found that responses to social cues were higher after the isolation condition, compared to fasting. And these responses, the strength of these neural responses was correlated with your self reported cravings. So the more you were craving food or social contact, the stronger the response in the brain.
They also showed a narrowing of focus. So when you had been fasting, not only was your hunger response strong, your response to social cues actually was lowered compared to baseline. So your brain was essentially really honing in on the object that you were craving, what you had been deprived of. And the same happened if you'd been in social isolation, your response to pictures of friends and social contact was heightened, but your response to food was actually lowered compared to baseline. So it kind of goes along with what we know about this narrowing of focus to focus on your goal of attaining that thing that you're desiring, that you're missing.
They did look at two other areas of the brain called the substantia nigra and the ventral tegmental areas. And these areas are really associated with food and drug cravings. Now they only showed the increased response to food after fasting. Those areas didn't show an increased response to images of social interaction after isolation. So those very specific areas didn't. The broader dopaminergic midbrain region did show that almost parallel response, that it shifted towards food when you'd been fasting and shifted towards images of social contact when you'd been in isolation.
Katie - So what does that mean then?
Helen - Well, it's really quite nice. We know that in mice, in the same areas of their brains, the dopaminergic midbrain, we know that when that area is activated, following social isolation, this leads them directly to seeking out social interaction. So it seems that it serves a purpose. And it would make sense that it goes hand-in-hand with this narrowing of focus. It seems that when this area is activated by a craving, whether it's for food or social interaction, you are motivated then to seek out that reward of finding that social interaction or food, which is lovely. And the narrowing of focus would suggest that it really, your brain is almost assisting you, "I really need this, go get this to the exclusion of everything else".
Pre-pandemic, this type of research would have been valuable for looking at things like prison inmates, or people with long-term health conditions that mean they're quite isolated from social contact. I think what will be quite interesting with this research is to look at factors that can alleviate this. So it would be really nice to see if, for example, a video call can satisfy our social cravings in the way that more direct social contact might satisfy that. So I think there's more research to be done here in response to the pandemic.
12:25 - The evolution of "puppy dog" eyes
The evolution of "puppy dog" eyes
Juliane Kaminski, University of Portsmouth
Here in the UK, we are certainly a nation of pet lovers! The UK charity PDSA reckons that over half of all adults have a pet. With marginally more of us having cats than dogs. But let’s start by talking about man’s best friend. Juliane Kaminski from the University of Portsmouth is interested in the evolution of human social interactions. And it turns out that studying man’s best friend - who shares quite a long evolutionary history with humans - can shed light on the human-dog relationship, and also, perhaps, how we came to be the way we are...
Juliane - Well dogs have obviously various ways to communicate with our owners. They can communicate through vocal communication, like barking and other sounds that they produce. They can communicate with their body postures and all kinds of things. But one form of communication that we became really interested in the recent years is what dogs do with their faces when they're looking at humans. So at their facial movements.
Katie - Is this where looking cute comes in?
Juliane - Yes, that's very much where looking cute comes in! Because we found that dogs produce a special eyebrow movement when they look at humans and that seems to be particularly appealing to humans. So humans have a really strong preference for dogs that produce that eyebrow movement.
Katie - It sounds like a very compelling theory, but you set out to investigate the science behind this. How do you go about studying this in a scientific way?
Juliane - Well, first of all, we were interested to see whether humans would really have a preference for dogs that produce that movement. And we did that by simply observing the behaviour of many different dogs in dog shelters. And we basically recorded all the kinds of behaviours that they produce when they meet a person. And then we asked the shelters to tell us how quickly those dogs were adopted. And we wanted to see if anything in the dog's behaviour made them to be adopted quicker than other dogs. And we found that it was particularly that facial movement that guaranteed a dog to be adopted faster than dogs that didn't produce that movement very often.
Katie - Can you describe this movement?
Juliane - It's what we call the puppy dog eyes. It's this moving the eyebrow up and a little bit inwards and it makes the dog face look really appealing to humans.
Katie - It's the kind of "help me, feed me, look after me".
Juliane - Yeah. It's a really interesting movement because it resembles a movement that humans produce when we are sad. So we have the theory that it might kind of trigger this natural response. So this kind of attention that we are directing at dogs comes from the same place that this kind of attention that we would direct at an infant, for example, that is producing this kind of movement. We are attending to this sad-looking creature.
Katie - Are dogs unique in this? Where did this particular movement or muscle that facilitates this movement come about?
Juliane - Yeah, we were really interested in that to see if there's any evidence that we humans might have unconsciously selected for this movement by simply preferring dogs that could use that movement and nurturing those dogs more. So we compared wolf faces and dog faces to see if there's any difference. And what we found is that the facial muscle structure of dog faces and wolf faces is almost identical. So the only difference is around the eyes. So exactly that muscle that produces this eyebrow movement is a muscle that we could find in dogs, but not in wolves. This is not something that happened consciously. So humans wouldn't have gone, "Oh, that's a really cute dog. Let me give that dog a little more food". So this is most likely something that happened unconsciously. So we simply had an unconscious preference for this movement, which kind of triggered this response of us wanting to attend to this creature. Therefore, we simply unconsciously selected this trait in dogs.
Katie - Kind of sounds like this says just as much about humans as it does about dogs.
Juliane - That's a really interesting aspect of this work. So it kind of raises a lot of hypotheses to some extent about our own species, so that these unconscious preferences can have such a strong or create such a strong selection pressure on another species. I think that's enormously interesting.
Katie - Do dogs use this muscle to communicate with anyone else? Other dogs, other species, or is it really particular to us?
Juliane - That's a very interesting question to which we do not have the answer yet, but that's one of the things that we are going to look at. And another very interesting question is whether dogs have in any way learned that this movement works with us. So is there any evidence that in some sense, they're producing this movement in an "intentional" way? So have they learned to manipulate us in any way? Or is it simply that they just produce that movement and it has no meaning for them? But it's simply humans selecting based on a trait that they find attractive, even though for the dogs themselves it means nothing.
Katie - Ultimately you're interested in how humans communicate with each other. So how does studying how dogs and humans communicate, how does that tell scientists like you about us? And how we communicate with one another?
Juliane - Well, I guess ultimately I'm interested in the evolution of these processes. So I'm interested in the evolution of human social interactions. And whenever we're interested in the evolution of something, we need to kind of find a model species that can help address some of these questions. And for many people, I guess, primates are the main model species when we are looking at human evolution. We might be interested in apes, as humans' closest living relatives. But dogs are fascinating model species because they have been domesticated and they've been living with us for such a long time. So the idea is that maybe this kind of evolution in a shared environment can kind of shed some light on some of the evolutionary processes in place.
19:37 - Cunning cat acoustics
Cunning cat acoustics
Karen McComb, University of Sussex
Animal behaviour expert Karen McComb told Katie Haylor about some of the cunning ways cats can communicate with us humans...
[Purr with high pitch within it]
Karen - Basically he used to wake me up with this very annoying purr. And in the summer he would do it from about 5:30 AM. You know, sit on the bed, really close to my face and do this purr. And I thought, "why is that purr so hard to ignore?", because you try and sort of pull the covers up and he didn't give up. And I just, I couldn't bear it. It was sort of really grating on my nerves. So I would eventually, you know, just get up and feed him.
There were other people who had these sorts of cats that did this very particular thing, particularly in the morning. I thought, "well, let's do a study on this and actually try and work out what it is about the purr that humans are finding so difficult to ignore". It turned out that there was actually a cry embedded in that purr.
So we think of the purr as a sort of pleasant, you know, low frequency noise, humans generally find that quite comforting.
But we were able to show that in the solicitation purr there was a high frequency noise about the frequency of both a cat cry and a baby cry -
[purr with high frequency within it]
- superimposed on the pattern of the purr. We had solicitation and non-solicitation purrs from 10 cats, one type of each, from each cat. And so we were able actually to play these back to humans, we were able to get humans to rate the pleasantness and urgency of the purrs. And at the same time, we were able to measure the acoustic characteristics of the purr. So we were actually able to zoom in on the ones that they find unpleasant and urgent and what acoustic characteristic was associated with that. And it was this high frequency peak embedded in the purr. And we were even able to remove the high-frequency peak and show that the urgency decreased and the pleasantness increased.
It seemed that cats were using this high frequency juxtaposition to, or it was having the effect, functionally, of tapping into human tendencies to nurture babies and to be very sensitive to the frequencies of a baby cry. It wasn't just that you learnt that that was something that meant they wanted action. It was actually, you were responding at an innate level to what they were doing. In fact, you weren't even aware of what they were doing, except that you find it unpleasant.
Katie - Do we understand that well how cats actually produce purrs? Is it quite complicated to have your general purr and then to layer a cry on top of it?
Karen - Cats produce purrs at a frequency that they shouldn't be able to produce really. I mean, it's in the mid twenties in terms of hertz. Now I would expect that frequency in an elephant, which has huge vocal folds and the fundamental frequency of the vocalisation is related to the size and the mass of the vocal folds. So usually when you vocalise, you force air from the lungs over the vocal folds, and they start vibrating at their own natural frequency. Cat vocal folds are going to be so small that there's no way that they would be giving you a fundamental frequency of 26 hertz, for example. But, instead of doing that normal voicing, when they produce a purr, cats are actually twitching their vocal folds, it's a muscle action that's allowing them to vibrate the vocal folds at that very low rate. The thing about that is it actually still then leaves the opportunity to add voicing to that mechanically produced purr. And so it seems with the solicitation purr that they are forcing air through the vocal folds at the same time, and the vocal folds are then able to vibrate at the much higher frequency of a cat cry. And that, as I say, interestingly is very similar to your baby cry. I mean, sometimes when you hear a cat cry, it's easy to confuse it with a baby cry anyway. So they just happen to be, you know, spot on.
Katie - There's a stereotype, isn't there, that cats have a very uncanny sense of timing. As you were telling me about the purr, one of my kittens jumped up onto the table, headbutted the microphone and purred into the microphone. Did you hear that?
Karen - I didn't!
Katie - I couldn't have made that up...
I think I'm a sucker, to be honest. I give my cats so much attention! But has there been any science done on the other side of the coin? Is it useful for me to talk to my cats? Or is that just me being a bit eccentric? Do they appreciate a vocal interaction with humans?
Karen - I think they do. I've always talked to my cats and I have a particular sort of undulating, frequency-modulated voice that I use with them. And that's the voice I would use with a cat in the street as well. I do think that they are more responsive to that. They learn that that's a positive social invitation from a human. Dogs - there's been work on dogs showing that they're more likely to respond to that sort of frequency-modulated type speech. Again, it's a bit like the way we speak to babies. Really
Katie - Another communication method - I noticed when I was about 10 by spending a lot of time with my big ginger tom who's sadly now passed on - is this idea of blinking. And you've also worked on cats communicating with humans via blinking. Can you tell us what you've shown?
Karen - Yes. Well, like you, I have always communicated in this way with my cats because actually it's something that cats do and they sort of teach you to do it inherently. If you live with cats, you notice that sometimes they narrow their eyes at you and then they close them completely and blink. And if you do this back to them, they respond in kind. So you can set up a really nice conversation in that way. Other people through their own pets were becoming aware of this, but there'd been no work showing, first of all, that humans can stimulate cats to do this back at them by slow blinking themselves. Or any work actually showing what the function of the slow blink was, you know, whether it really was, we get the impression that it's a positive form of communication, but how would you show that?
So we set out - I had a PhD student who worked on this - Tamsin Humphrey. We showed not only that cats were more likely to slow blink, and this was at an experimenter when the experimenter blinked at them. But also if the experimenter had gone through a slow blinking session with them, rather than just sitting with a neutral face, then at the end of the experiment, the cat was more likely to approach and sniff the experimenter's hand. It was seen as a positive by cats when humans, even humans that they didn't know, did this with them. And we had a parallel set of experiments getting humans to do this with their own cats. And of course the cat was more likely to respond when they did that. Then if the human was just sitting with a neutral face.
Katie - On some sort of very basic level, if I close my eyes, when I'm in front of someone, I'm trusting that they're not going to eat me or fight me or something. Is it kind of a lowering of defenses type thing?
Karen - I've always thought that. It's sort of a, "I'm cool. You're cool. So I can take my eyes off you for a minute. And I feel comfortable in your presence". I mean, it's also got very interesting parallels with the genuine smile and humans.
Audio clips of purrs are from the Current Biology below.
28:60 - Pets and mental health
Pets and mental health
Helen Brooks, University of Manchester
Back in 2018, Helen Brooks at the University of Manchester conducted a review of studies examining the impact of keeping pets on people’s abilities to manage mental health conditions, and Katie Haylor spoke to her about it...
Helen - So I think as a pet owner myself, I can obviously appreciate the value that my dogs have in terms of my mental health. Getting me out, connecting with nature. But I was really surprised by the range and the depth of connection that people talked about with animals. And the range of different ways that they were helping people to manage their mental health conditions, in particular around how important pets were in terms of distracting them from symptoms. So things like hearing voices, feeling depressed.
We wanted to systematically look at the research that had been published, that looked at the role of companion animals for people with a diagnosed mental health problem. So we searched in a systematic way, all the databases, also unpublished literature. So we could bring this evidence together and really see what we knew about the topic.
Katie - I'm assuming that having a pet is a good idea if you're managing a mental health condition, is that what you found?
Helen - It's quite a complicated relationship. And I think that speaks to the mixed results that we found when we did this review. And there's a number of factors which impact on the relationship between having a pet and mental health outcomes. So things like the type of pet, the number of pets that a person has, and interestingly how friendly the animal is perceived to be by others. So we managed to identify 17 studies from all across the world that had looked at this topic. And in 15 of those 17 articles, there were positive aspects of pet ownership for people with a diagnosed mental health condition. Nine out of the 17 studies also identified negative aspects and there was a number that identified no relationships between the two.
Katie - Does it depend on the type of mental health condition? Because if you're really anxious, I guess you could be anxious about your pet's welfare, but also a pet could have a calming effect.
Helen - The review didn't look particularly at different types of mental health conditions. What was most important, I think, was whether the person had the capacity and capabilities to be able to manage and look after a pet in terms of feeding, grooming, exercising, cost as well. So where the person was able to successfully care for an animal, then they really felt strongly that they had a positive impact in terms of managing their mental health.
Katie - Does it break down by animal?
Helen - So no, generally speaking, the research tended to include pets as one whole category. Interestingly, what you can find is that for dog owners, that's particularly important in terms of encouraging exercise. And there was a weak trend towards pets being important in terms of helping people manage the experience of being diagnosed with a health condition.
Katie - I guess with a dog, you have to walk a dog, right? So you have to get out and I can see how the necessity of physical exercise might be good for your mental health. But if you've got cats or an animal that generally doesn't like to be walked, are you still getting a benefit?
Helen - Yeah, there was actually a lot of benefit. So in terms of emotional support, having a companion animal was really important. So just having someone around that was a consistent presence. That being available to you without having to ask for it was really important. And that was true of all different types of animals included in the review.
Katie - And we're not just talking about fluffy things that might like to sit on your lap.
Helen - There was a real wide range of animals included in the papers that we looked at. Generally speaking, they were mostly cats and dogs, but there were some things like bearded dragons. And what was really important was that people were able to select an animal that really fitted with their lifestyle and their ability to manage with a pet.
Katie - What do you make of this then? Would it be too extreme to say pets should kind of, be on prescription, as it were?
Helen - It is more complicated than that. And I think our results showed that. So the mixed results that we found in the different papers that we included really speaks to the complexity in the relationship between having an animal and your ability to manage a mental health condition. So there's a number of things we need to take into account. Obviously, the welfare of the animal. And making sure that the animal and their owner are well-suited. Again, it's the number of animals is really important. And how friendly that animal is seen to others. So it's quite a complicated relationship. A lot of people feel that their pets are really important way of increasing social interactions. So not only improving relationships with existing friends and family say, but also increasing what we call contact with familiar strangers. So people in our local community who we might not know particularly well, but we can have valued social interactions with them. And dogs particularly are helpful in terms of facilitating those. So other the dog walkers, I know people talked about staying connected to the community through seeing churches being rebuilt or new buildings going up because they were out walking the dogs and speaking to people on the sites. So it's those social interactions where I think probably that finding's most pertinent to.
Katie - What do you think people should take away from this?
Helen - Whilst taking the caveats and some inadequacies of the data into account, I think the review really showed how important pets were to people with a mental health problem. And I think the key thing for me was about making sure that people in health services understood and recognised this. Because we know how distressing it can be when people are separated from their pets, when they have to go into the hospital or when they're acutely unwell. So I think it's about making sure the importance of people's relationships with their pets is really taken into account within health services.
Katie - It's really interesting you mentioned that, although the bias is in favour of it being good for managing a mental health condition, there were some people who experienced negative consequences.
Helen - Yeah. So I think it's really important to say that the people that we spoke to, the people that were included in the qualitative work that was in this review, were successfully managing owning a pet. And the people, I guess, who have recently given up a pet weren't really included in the papers that we looked at. So even the ones that were successfully managing the work of owning a pet talked about negative aspects such as cost, the emotional burden of looking after an animal when you're feeling unable to look after yourself in some cases, was difficult. There was also - which I wasn't expecting - a real concern about a future loss of a pet. So often people rely very heavily on this relationship with their animal in terms of managing their mental health. And they were really concerned about what would happen in the future, should the pet die or be taken away from them. But we should also say that, when taken altogether, the negative aspects were outweighed by the positive aspects that people reported in these interviews.