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To Calm a Rat with Tickling

The views expressed are those of the author and are not necessarily those of Scientific American.


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“for here comes the trout that must be caught with tickling”
-Twelfth Night

Generally, I don’t think of being tickled as a particularly pleasurable or calming activity. Most people who are ticklish go immediately on the defensive and tense up, and I always got the impression that most people prefer NOT to be tickled rather than otherwise.

However, that’s just us. And we’re not rats. And it turns out, you can calm a rat with tickling.


(Source)

Note: I’ll admit, I’m covering this paper primarily because I love the idea of tickling rats. ADORABLE!

Hori et al. “Effects of repeated tickling on conditioned fear and hormonal responses in socially isolated rats” Neuroscience Letters, 2013.

Life is stressful. Whether it’s running from predators, meeting tight deadlines, or trying to keep fed, there’s a lot that seems to bring us down.

What saves us from tearing our hair out? Well, the happy things in life. Tasty food, friends, hugs, puppies. You know, the good stuff. These things elicit positive feeling, and positive feeling have been linked to protecting us from stress.

Of course, in humans, it’s easy to say that a positive outlook on life makes someone resistant to stress…but is it really true? They may co-occur, but do positive feelings really decrease stress? If you want to get at causes, one of the best ways is to use an animal model. But how do you come up with an animal model for…happiness?

Well, you can tickle rats.

As you can see in the video above, rats like to be tickled. They even respond with “laughter”! Of course, it’s not laughter as we know it, or even something we can hear. Instead, these are ultrasonic vocalizations at a specific frequency (50 kilohertz). Scientists figured they must be pleasure-sounds because rats make them when they play with other rats. And it turns out that rats make the same noise at the same frequency when they get tickled!

A rat’s happiness at being tickled presents a good possible model for how positive interventions (like tickling), could change their response to stress, and could therefore help answer the question of whether positive things really CAN change stress response.

And of course, it also means you get to tickle rats daily. Who could argue with that? It’s like “oh DARN, I have to go snuggle some kitties today! My life SUCKS”*

For the “tickling treatment”, rats were tickled once daily, in two sessions of two minutes each, for two weeks. The rats were housed individually otherwise, something which is pretty stressful to rats.

Here you can see the responses of the rats being tickled. After a little bit of training, the rats recognize what’s going on, and head right over to the experimenter’s hand to get tickled as soon as he puts his hand in the cage. They also make those ultrasonic vocalizations associated with little rat happiness.

After half of the rats had been tickled for two weeks, the authors gave them something called fear conditioning. It’s where you put a rat in a chamber, and pair the sound of a tone with a painful shock. It’s a memorable experience, when you expose the rat to the tone again, the rats will freeze in place waiting for the shock, even though there is no shock coming at all. This test is often used as a test for memory, but it also works well when looking at stress, because if you give treatments that reduce stress, you can reduce the freezing response after training.

So did tickling reduce stress?

You can see on the left the test for fear two days after the training. There’s no difference. But on the right, you can see the test for fear 5 days after training. While the untickled rats are still freezing a lot, the tickled ones are freezing significantly less. It appears that the tickling helped with the painful memory of the shock.

The authors also wanted to look at the biological aspects of stress response. They looked at two neurotransmitters, adrenaline (epinephrine), and noradrenaline (norepinehprine), two chemicals in the body that respond particularly to stress.

They were able to show that tickling the rats resulting in less adrenaline and noradrenaline release following fear testing. They also looked at corticosterone, a hormone very much involved in the stress response, but couldn’t find any differences.

But it looks like tickling rats can protect against some of the effects of stress. The intervention doesn’t appear to be big, as there aren’t changes in corticosterone, but it’s enough to produce a behavioral effect.

It’d be interesting to see how this compares to other things that can ease rat stress, like say, group housing in your buddies, enrichment of other kinds (rat playgrounds), or drug interventions (like Prozac). And it would also have been good to see how the rats being tickled responded in other measures of anxiety.

It’s too bad that they didn’t get any differences in plasma corticosterone. Increases in plasma corticosterone during and after stress are often the best indicators (or at least, they are the ones taken more often) of a stress response to something like fear conditioning. But I have to wonder if they didn’t get anything here because of timing. They were testing memory retrieval, not the initial stress response itself. And so I wonder if the corticosterone response to the initial stress (right after the shocks had been given) might have been lower in the tickled rats.

But regardless, it’s an interesting model of how the good things in life could help mitigate the bad ones. And while a lot more remains to be done, and we humans may not love getting tickled like rats do, it may mean that other positive feelings could have some effects on our stress responses, too. So take a deep breath, find a friend, and tickle a rat. It certainly wouldn’t do anyone any harm.

*Seriously, rats get a bad rap. Most domestic rats (experimental and fancy pet style) are charming and very snuggly and friendly. Well worth daily tickling.

Scicurious About the Author: Scicurious is a PhD in Physiology, and is currently a postdoc in biomedical research. She loves the brain. And so should you. Follow on Twitter @Scicurious.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. doc_becca 11:45 am 04/22/2013

    Great write up! I agree that it’s too bad they didn’t look at cort and adrenaline/noradrenaline levels after an acute stressor or fear conditioning–baseline levels don’t mean much if they’re able to compensate for that in response to a stressful stimulus. But my hunch is that you’re right, they probably would have seen a reduction if they’d taken blood then.

    But I don’t think there’s enough evidence to say that their effects are “stress”-related, and not simply memory-based. Both cort and NA release are critical to the long-term maintenance of fear conditioning memories, so if the tickling reduces those factors, all they could be looking at is a long-term memory deficit.

    Finally, do you think it’s weird that the tickling takes place with the animals on their backs? In other circumstances, this is the “submissive” position of a rat that’s losing a fight. I would imagine there’s got to be some sort of innate circuit activation associated with physically being in that position.

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  2. 2. scicurious 1:40 pm 04/22/2013

    Hi Becca!

    Yes, I was thinking about that, you can’t really take the stress aspect out from the memory aspect in fear conditioning. Maybe next time they should try something like chronic mild stress and look at those effects.

    As far as the tickling on the back, yes that’s submission when losing a fight, but rats respond different when in a play situation in adolescents, where they will emit those vocalizations while on their backs. This is the rationale for the tickling, that the play is positive (deficits in play are associated with stress, etc), and the vocalizations are indicative of a positive experience.

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  3. 3. rjr20 4:11 pm 04/22/2013

    What I really want to know is whether it made the humans less stressed too. I used to have pet rats and tickling them really cheered me up. Are the scientists then re-stressed by having to give the rats electric shocks? I would like to know more about stress in people who do stress tests on animals.

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  4. 4. Bett 3:27 pm 04/23/2013

    Cute and interesting until you get to the part where the [expletive deleted] were shocking and causing fear in the rats. [Expletive deleted.]

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  5. 5. greg_t_laden 9:30 am 04/24/2013

    How does this relate to Garcia’s “Rat in the can” experiments?

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  6. 6. Gorgonetta 9:36 am 04/24/2013

    This is incredibly old “news.” The research was first done in the mid 90s by Panksepp and Burgdorf. And as Bett pointed out, there’s nothing cute about animal abuse. Aside from torture inflicted during the course of the experiment, every single one of these animals was put to death afterwards because their usefulness had reached its conclusion. This is standard practice. It’s not precious and it’s not cute. Additionally, there’s nothing in their findings that loving, observant rat keepers hadn’t known for years–but researchers, coming from a position of of dominance and authority, are too wrapped up in themselves to simply *observe* their charges, which requires humility.

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  7. 7. scicurious 9:42 am 04/24/2013

    Gorgonetta and Bett,

    Yes, we have known for a while that tickling in rats is a positive experience. And yes, fear conditioning is not a happy paradigm, and the rats were sacrificed for further studies at the end of the experiments. However, research like this is extremely important for discovering mechanisms of how animals, and humans, experience and combat stress. Given the environmental stress of many animal species, and the extremely detrimental effects of stress on humans (leading to increased risk of depression, cardiovascular disease, cancer, etc), it is very important that we carefully study the different ways to combat stress, particularly behavioral ones which may be easier and better to implement than things like drugs.

    It is also important to understand that there are incredibly high welfare standards for how rats in these studies are treated. The vast majority of scientists treat their animals with the utmost respect. We respect what they do for us, and we do not enjoy hurting them. But we also acknowledge the importance of what our studies will lead to, treatments and understanding of behaviors and physiology for both animals and humans.

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  8. 8. Morgainele 8:53 pm 04/24/2013

    Incredibly high welfare standards? Really??? Like what?

    So, when you are not shocking and then giving positive touch, then shocking again to watch their changes in fear response… i.e. when you are not TORTURING the poor little beings… they are then treated well? Methinks the torture makes whatever happens in between kind of moot.

    Also please share, what do we now know that we didn’t before about how to behaviorally help humans under stress? We have plenty of shell shocked humans who would gladly voluntarily take part in behavioral studies to find methods to reduce stress without medication…so againb what is the REAL positive that comes out of this rat torture?

    We know that rats, like all mammals (from science which verifes our own intuitions ) experience a range of emotions. Your own research admits as much. We know they feel pain, experience fear and anxiety…and some measure of perhaps joy, or at least pleasure, as seen in the tickle response and something akin to laughter- (now THAT should be eliciting some curiosity about what ELSE they are capable of “feeling”) So… in terms of their own desire to live…how can you say they are really all that different from severely intellectually impaired humans, who can’t speak or do math or think abstractly, but do experience varying levels of joy of familial affection, the peace of being held, the fear of painful associations, the AGONY of pain– the laughter of being tickled or playing with ones mates- perhaps even grief when watching another suffer???

    In terms of any physiological data you hope to gain, have you not read the findings – (again reinforced just in February) that mouse models do not accurately reflect the genetic and proteomic responses to acute inflammatory stress in humans,(Proceedings of the National Academy of Sciences) More and more we are hearing the emphasis on the need for research on human physiology.

    Bottom line- this is unadulterated animal cruelty. It sickens me to hear how cavalier those involved can be about this. And please don’t soften the reality by using the word “sacrificed.” They were KILLED. We humans didn’t sacrifice ANYTHING. They suffered some variety of hell. And for what grand good?

    Finally, how would you like it if some intellectually advanced alien species came to earth and decided that because you are by their measures – intellectually disabled, it was morally justified to put you in a cage, put you through similar studies as you do with rats, then as they “sacrificed” you, said in a language you couldnt fathom, “thank you for your help, we hold great respect for what knowledge you are bringing us?”

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  9. 9. scicurious 9:19 pm 04/24/2013

    Morgainele,

    First, in fear conditioning, rats are only ever shocked during the training session. In testing (in this case at 48 and 96 hours), they are put in the environment only, with no shock.

    In terms of welfare standards, animal researchers are held to the very highest standards of cleanliness, and centers often have a large staff devoted to cleaning cages (each cage before use must be entirely sterile) and monitoring every animal daily. In addition, a trained team of veterinarians examines every animal daily. When not required for the purposes of the experiment, every animal is required to be housed with others, so that they have social contact. Their cages contain fresh food and water, ad lib, at all times. They are also given toys, hutches, and other things to make nests and chew on. Before any research is done, all protocols have to written out in full detail and presented to an Animal Care and Use Committee, which is composed of scientists, veterinarians, and members of the public (you can, in fact, volunteer to be on one). They ensure that if an animal will be in pain, that pain is treated with painkillers, and that there are no unacceptable studies getting through. They also carefully analyze how many animals will be used and of what type. If you can use E. Coli instead of a mouse, they will insist that you use that instead. We do our best to use as few animals as possible while conducting research that is as solid as we can make it.

    And I have in fact read the findings you reference. First, these are rats, not mice. Secondly, as far as is currently known, the data referenced only refers to inflammatory cytokine profiles, not to things like stress. On the contrary, there are many studies showing that rodent stress models and the ways they are treated translate very readily to humans. And it is important that experiments studying how stress is managed have proper controls. There are many humans studies of stress as well, most of which build on, and put into practice, studies from animals. I have myself volunteered for many human studies, I consider it my duty to contribute to science with myself as a subject whenever possible.

    I do not think that I can convince you, and I do understand your feelings. No one WANTS to hurt animals. No one enjoys doing it. But at the same time, no one wants to see the results of untreated medical conditions. We want to find cures and treatments. And for that, right now, we need animals.

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  10. 10. bucketofsquid 2:03 pm 05/1/2013

    If you don’t like animal testing then volunteer to be test subjects for these early round tests. Keep in mind that many of these forms of testing will severely injure or kill you. While I value animal life, I value human life higher. Anyone that studies nature comes to know that most animals die by being eaten alive or wasting disease or sometimes both. There are also the mass starvation cycles that periodically kill off the bulk of one or more species in an area due to a lack of predators.

    Food cattle and lab rats live longer than their wild cousins and usually die quickly rather than being ripped to pieces by a predator while they still live. You can call yourself humane all you want and point the stinky finger at those that make the world better but is a lie. Unless you are a vegan and don’t wear clothes ever and live in a cave, you are contributing to the exploitation of some form of animal. If you are a vegan then most of what you eat comes from cruelly exploiting plants.

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