Sci-Fi Today: Ultrasonic Vocalizations

Sometimes it's about what we can't hear...

Okay, let me be up front and say that this was not the originally planned Sci-Fi Today that I was going to post before the end of this year. And yet, I’ve been struck with a stroke of inspiration that I can’t ignore! Therefore, I come to you with a new concept that I think is rich with writing inspiration and is also just a fascinating thing to learn about. I don’t expect this entry to be exceptionally detailed, but I will share as much as I think is appropriate and as always share my sources so you can delve deeper if you’re interested. So, without further ado, I give you… Ultrasonic vocalizations (USVs).

Before we get into this, I’d like to welcome you to the third installment in Sci-Fi today. So far we’ve talked about Transcranial Magnetic Stimulation, glia, and now USVs. It’s quite a wide array of concepts. There’s so many fascinating things to discuss in the world of neuroscience that I’m being relatively picky on what I want to write about and what I don’t. Maybe one day I’ll be scraping the bottom of the barrel, but for now I’ll be picking and choosing things that I find especially interesting. The promised 4th installment will be coming in the new year at some point. I’ll admit it has been an extremely difficult concept that I don’t work with personally, so it's taking a lot more reading on my part than the already written Sci-Fi Today projects usually require of me, so pardon the time I’m taking. Okay, with all that out of the way, let’s talk about USVs…

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The Science…

What in the world is a USV? Well, it is exactly as it says. It is a vocalization that is in the range of being ultrasonic meaning they are in the upper limits of what can be heard in hertz (Hz) or kilohertz (kHz). These are sounds that cannot be detected by the human ear - we just don’t have that range limit! Human hearing range is about 20Hz-20,000Hz, whereas ultrasonic would be considered above 20,000Hz or 20kHz! Something that will always amaze me is how easy it is for we as humans to think what we perceive and experience is all there is, but there are so many reasons that isn’t true from just our brain filtering out unnecessary information, to our biological systems not being capable of detecting things at all! Or maybe we just aren’t paying attention, who can say? Regardless, the reasons we don’t perceive things are just as interesting to me as the reason why we perceive things. But there are many other animals with very unique ways of perceiving the world, and USVs are just another part of that.

As I said, there are many different animals that perform sounds in the ultrasonic range, but because of my own personal experience, I’ll be focusing on mice and rats! I have extensive experience handling mice and rats - as many neuroscientists do - but I’m pretty certain different insects, bats, and many other animals can perform vocalizations in the range of ultrasonic. And yet, mice and rats are the animals I know best out of them all.

So what exactly is happening during a USV? In my mind it feels almost like a secret language. They’re literally communicating in a range we can’t hear to convey things that we don’t understand - at least we didn’t at first. To be clear, we don’t entirely understand what all these USVs are yet, but depending on the animal, their sex, and their age, they perform them for different reasons at different times. For those of you who think that mice and rat’s only difference is their size, I have some bad news. They are in fact extremely different and the context in which they perform USVs are also different. Here, let me highlight some real quick.

Rats

Rats utilize USVs much more often than mice do, and much more frequently throughout their lives. Most of the papers I went through for this had a ton of reasons under specific circumstances and behaviors in which a rat would perform a USV. Mice? Less so, but still in many cases. Here’s some of my favorites:

• There’s been extensive research showing that rats are ticklish! And when you tickle them, guess what? They vocalize in an ultrasonic range. This is technically referred to as a social buffering vocalization! Why else?

• Young rat pups do it when they’re separated from their mother. Though interestingly after 14 days old, they’ll stop doing it when a male is nearby - important to note that male rats are very mean to pups the older they get and will sometimes kill them and eat them so they can have the mother to themself or if they think maturing males may be competition.

• Speaking of males, male rats also do it when courting female rats, and will continue doing it while having sex. Something I find interesting about this is that they don’t know if females are also doing it, or if it's just males. I found some interesting discussions about this with mice, but not rats so stay tuned for that.

• They also use these calls with familiar rats. I think in a way this would be similar to speaking differently to your friends than you would a stranger which is fun to think about! There’s a few different types of vocalizations that rats utilize for communication in social interaction that fall into specific subgroups (phatic, affilative, and passive defense, and even more).

• There’s also the extremely interesting socio-ccoordination interaction that's involved in group activities and how they coordinate amongst themselves. The paper I’m reading specifically points to the importance of this in rough and tumble play which I find especially interesting. It sort of reminds me of how dogs sneeze and keep their tails up during play in the ‘we cool?’ ‘yeah, we cool.’ way that keeps play as just that and not a fight. Not to say this is what it is, but it's just what it reminds me of to be clear.

• More sadly, rats will also utilize USV when they’re in pain. For example, if you were to shock a rat, they will emit a USV.

I’ll be honest, there are A LOT of reasons that rats will use ultrasonic vocalizations. Like a lot a lot. So I’m going to link the review I’ve been utilizing for this right here, so if you want you can have a look for yourself. This is a fairly approachable one and it is open sourced so I encourage you to pop it open and skim through if you’re curious!

https://pmc.ncbi.nlm.nih.gov/articles/PMC8150717/#:~:text=The%20emission%20of%20juvenile%20broadband

It is also important to note that these sounds are all within a range of kHz Most of what I’ve seen says that rats emit anywhere from 20kHz to 100kHz. But what about mice? I said mice are different, so let's look at that real quick. Just to start, their ultrasonic range is different! They vocalize in an ultrasonic range of 30kHz to 110! So we already see a difference in their range! What else?

Mice

• Much like rats, mice engage in USV when separated from their mother or when they’re separated from their nest and they start to do it less and less by two weeks old until they barely do it at all. But they still do it!

• Much like rats, they perform it specifically when males and females are interacting. Interestingly, most researchers think it's just the males who do it, but some think it's both. When males who were unable to perform USVs were put into these social situations (mostly sexual) with female mice, there were no vocalizations. But to be fair, who is to say that females just aren’t doing it because the males aren’t? As far as I can tell, we don’t know if that’s the case. It could be males only performing USVs or it could be that males initiate USVs.

  • It may seem like a small difference but that could be telling of social behavior. I didn’t see anything in the paper that indicates that a lack of USVs change behavior, but I would assume it would. I wonder…

  • Mice will also perform USVs when nesting in groups. I’m assuming this is similar to how rats will do it when they’re with ‘friends.’

• Mice will also vocalize when presented with threatening smells.

  • Isn’t it interesting that to a mouse, the smell of a rat is threatening? Yes, rats are a predator of mice, so the smell of a rat can be very threatening to the much much smaller mouse.

  • A threatening smell to a mouse pup can also be that of an adult male mouse, because much like their rat counterparts, male mice are not the biggest fans of maturing mice - especially when they aren’t their own.

    • (Interesting sidenote: different strains of male mice are actually considered ‘better’ or ‘worse’ parents! Broadly speaking, male mice aren’t really considered father of the year types, and in fact in many breeding colonies will remove the males after pups are born to prevent them mistreating the pups, BUT in certain mouse strains - I personally work with the C57Bl6 mouse for example - they can actually be pretty good parents. Ironically, female C57s have a bit of a reputation - even though I haven’t personally seen it or read any papers that have discussed it - for being worse than average mothers. But C57 males are considered relatively good fathers. Keep in mind, relatively good still isn’t as good as the less good than average mothers, but it is still interesting. Also note that use of ‘better’ ‘worse’ ‘good’ and ‘bad’ are just for simplicity’s sake in discussion. That isn’t the exact terminology that is preferred in the field.)

Anyway, much like the rats, there are even more complex reasons than the simple concepts I’m presenting here, so if you’re interested in more details, I encourage you to check out more here: https://pmc.ncbi.nlm.nih.gov/articles/PMC8224126/

All this is to say: There’s a lot more going on in the animal kingdom than we can even begin to hear or understand. There’s certain behaviors that many are quick to cite as instinct or just learned behavior, but it appears that some of that behavior is in fact caused by communication at different frequencies that send different messages. What we may see as a mother instinctually running to where her pup has left the nest, may be here responding directly to the sound of her pup calling for help. Interestingly, the question in rodents of if this is learned behavior or something innate appears to still be up in the air from what I’ve read, but I’d be interested to find out when researchers figure out a way to test that hypothesis.

And before we move on, I want to show you an example from the above paper where they show what different kinds of communication look like when measuring USVs. I personally have been using ‘Deep Squeak’ in collaboration with another lab which gives us much prettier pictures than this does, but alas I can’t show you my own data at this time - maybe once it's published. stay tuned for that! Anyway, have a look at this fascinating figure from Premoli et. al 2020:

Examples of types of USVs taken from mice communication patterns.

Interesting note: They point out that they collected this data using Avisoft Bioacoustics. I myself use Avisoft equipment, but as someone who is not a USV expert, I find Avisoft’s software package absolutely baffling to use. I’ve never felt more clueless than when I tried to just analyze my data utilizing Avisoft’s software. So in my experience, Avisoft has amazing capture equipment, but impenetrable analysis equipment unless this is your area of expertise. Deep Squeak is much easier to approach for someone new to USV analysis. So in conclusion, collect data using Avisoft equipment, analyze using Deep Squeak (which is free by the way, unlike Avisoft’s analysis package). As a matter of fact, here’s a quick look at Deep Squeak’s analysis (oh no, is this a Deep Squeak ad now?):

A collection of images analyzing rat USVs through Deep Squeak. Image from: https://www.nature.com/articles/s41386-018-0303-6 Note that Deep Squeak uses machine learning, which in this case helps researchers not have to parse through all the data for literally days. Something that would typically take multiple days can be done in only a couple hours. This is one use of machine learning I can definitely get behind.

Is it language? Well, I’m no linguist, but I would say no. Is it simple communication? Absolutely. It makes me wonder about a lot of things from the perspective of a researcher, and rest assured I am exploring some of that in my work. But what about as a writer? Well, that’s why we’re here after all, aren’t we?

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The Fiction

With all that science nonsense out of the way, let’s talk about the fiction of it all! Personally, I think there is a lot of potential in this - from super powers to alien invaders to psychological horror. Now, I’ve heard these USVs myself - from a mouse and through an amplifier - and I’ll tell you this much - actually, let me paint you a picture:

You’re a scientist sitting there hoping to whoever will listen that your experimental design will work. You have your personal headphones plugged into some experimental equipment and you’re just hoping beyond hope that it will work.

You snap snap snap your fingers in front of the microphone. Okay, it kind of worked, but… that isn’t ultrasonic is it? So why would it work? The heavy creaking of machinery that you swear you’ve never noticed before is registered on the expensive microphone, yet when you clear your throat you hear nothing. Strange? So you decide to start the experiment.

You get up from your seat in the room, open the cage, and you grab a little tiny 10 day old mouse - of course when you really do it, they’ll be younger than this, but you just need to confirm that it's working, so it isn’t like you’re collecting the data anyway. You place it inside the testing chamber. Returning to your seat, you hit the record button on the computer and you tune your ears, hand on pen, getting ready to take notes in your notebook. How will it sound? What will it look like in the recording? What if you can’t hear it at all? And then…

You hear the most fascinating noise.

Like morning has come. Like the sun is about to rise on an early summer day. It's 4am, and the birds are awake. The birds - perhaps a robin, or a bluejay, or who knows what magnificent flying creatures sing to you from the tree beyond your window - sing in a chorus that only your headphones pick up and then… wait.

That chirp chirp chirp? That’s not a bird. It’s a mouse! A baby mouse, calling to their mother who is just a cage over wondering where you took one of her 9 children. The pup calls and calls. It wanders around, and the little pitter patter of its footprints are revealed to you in a way you thought you’d never hear.

Imagine if you could hear all of that. Imagine what the world sounds like to them. What does the frantic tap tap tap of a keyboard sound like, what does that sound of water - of air - of every little thing rushing around you sound like when your ears pick up a whole new world, a whole new way of seeing things? It’s magical in a way. It’s beautiful, and strange, and surreal, and I just can’t help wondering: Why can’t we as writers tap into the unseen? More importantly in this case, the unheard? To any animal, things don’t sound the same. The listening range is just a little tiny different. I can hear through an amplifier, but I can’t really hear it. I’ll never truly experience it, and that’s because my ears, my brain, my physiology doesn’t do that.

But can’t I create a world where it does? I could, couldn’t I?

So what if there was a hero with ultra sensitive hearing? Origin story? He found out because he could hear mice nesting in the walls of an old abandoned building! I know, this is an especially comical example, but my brother often says if I were a superhero I’d be Mouse-Man due to my extensive experience with mice and the ease with which I handle them, so maybe that’d be my own personal superhero origin story that at the very least would give my brother a laugh and probably get me hurt by my ever loving and ferocious cat.

Okay, new idea: what if aliens invaded and they were so silent, so quiet to us, but it was because everything they said, used and operated was occurring outside of our hearing range? The Silent Invasion does have a cool ring to it, though maybe we’re a little past sci-fi invasion stories perhaps?

Okay, last concept idea: imagine a man going mad in the streets of a sinking city who screams a silent scream and can only hear the earth-shattering, yet silent groans of the great old one rising from the depths. The survivors are the cult-like followers the mad man collects around him with his warnings of the end and the ever hesitant detective that happens to follow their ravings in the hopes it may point them in the direction of a prolific ritualistic killer in the city. I think this one may have gotten its sharp claws into me…

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Without ever explaining the scientific side of it, this could be a really useful starting place for why something happens. As a writer, I often love to have background starting info that may never come up in the story, but will be an important foundation for the story to rest upon. To give a more basic example, in my recent horror story, An Effigy to Contagion, We Devour in Excess, I for some reason struggled to write the story without a name for the protagonist. I usually don’t have that problem, I love unnamed protagonists, but I needed to name him. So I named him Daniel. Funny thing though? I never used his name a single time in the entire story. Funny how that works.

And yet, scientific baseline for why something works, can flesh a world out in such fascinating and beautiful ways, even if it isn’t the only focus or intent of your story. Might the reason your hero has such good hearing be because they have enhanced auditory range? Well, that would certainly be a good launching point. It would almost be like defining rules for how an ability works. Or… as I often like to say, it’s establishing the scaffolding.

I try to say in these how science is the scaffolding by which we build around and above to create our sci-fi. Sometimes we go far beyond our scaffolding. Sometimes we hang close to it. Regardless, a strong scaffolding goes a long way, doesn’t it?

So at the end of this, I offer you the same offering I would like to bring to any of these: Do you find this inspiring? Does it give you a flash of a possibility you hadn’t considered before? If so, I hope you try to use it to write something up, and if you do, please share it with me!

In the meantime, I have an idea of my own, and it happens to fit very well into a specific holiday collaborative project that I will be linking to below:

Christmas in Selene City

So as before, I’m giving myself a week to write a story inspired by this concept, but this time it will be within the confines of this collaborative story. I do hope you enjoy it, and I’ll tell you that I’m looking forward to the outcome. I’ll see you next week with said tale. And for those of you wondering about the next installment in this tale, just wait until the next Sci-Fi Today. I have two words for you: Nightmare Fuel. But until then, I’ll see you next week with a new short story!

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