As It Happens

Q: Why did the scientist tickle the rat? A: It wasn't just for laughs

Researchers in Germany tickled lab rats to gain insight into how the human brain regulates mood. Host Carol Off speaks with neuroscientist Shimpei Ishiyama.
(Shimpei Ishiyama)

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A pair of neuroscientists in Germany recently set out to answer a question: What happens when you tickle a rat?
     
The answer was delightful. But it also gave them insight into how the human brain regulates mood. Their findings have been published in the journal Science.

Shimpei Ishiyama is one of the study's authors at the Humboldt University of Berlin. He spoke with As it Happens host Carol Off. Here is some of their conversation.

"[I]ndeed, rats are also ticklish — they do vocalize when they're tickled. This special vocalization is indicating positive emotions, such as happiness or joy.- Shimpei Ishiyama, neuroscientist at the Humboldt University of Berlin

Carol Off: Mr. Ishiyama, how do you go about tackling a rat?

Shimpei Ishiyama: Ticklishness is one of the most mysterious sensations in humans also. So even though ticklishness is so common in human culture, we don't know why we laugh when we are tickled. And we can't tickle ourselves. There are so many mysteries. And, indeed, rats are also ticklish — that means they do vocalize when they're tickled. So this special vocalization is indicating positive emotions, such as happiness or joy.

"Their vocalization is ultrasound. So it's so high that we humans can't hear [it]. There's a special microphone which can capture ultrasound, and the computer just transposes the sound to the lower frequency, so that we can hear it." -Shimpei Ishiyama

CO: We have a bit of the sound that rats make when they are tickled. And so let's just have a listen. What are you doing when the rats are making that sound?

(Shimpei Ishiyama)

SI: So I flip over the rat, and push them back on the floor. And I move my finger rapidly on their belly. So the belly is the most ticklish part of the rat. And actually their vocalization is ultrasound. So it's so high that we humans can't hear [it]. And so there's a special microphone which can capture ultrasound, and the computer just transposes the sound to the lower frequency, so that we can hear it.

CO: It sounds like us giggling.

SI: Yes, or some scientists call it "rats' laughter".

"I tickle them firmly — kind of vigorously on their belly. And that's the way to make them laugh.- Shimpei Ishiyama

CO: What conditions are they most likely to enjoy being tickled? I'm sure it must be must be scary for them to see someone coming at them with a human hand. So how do you get them in the mood?

How lab rats react to being tickled

6 years ago
Duration 1:11
Neuroscientist Shimpei Ishiyama discovers that tickling a rat induces vocalizations, or 'rat laughter'

SI: Yeah, if you take a look at the video, it looks like it's rather like a firm shaking of]their body rather than tickling. So this is actually how they play with each other. They actually play very hard. It's also called "rough and tumble play". It's a technical scientific term of rat play.

(Shimpei Ishiyama)

CO: "Rough and tumble play" is a technical term?

SI: Yes. I also tickle them firmly — so kind of vigorously on their belly, and that's the way to make them laugh.

CO: Now you also discovered that, like humans, they will anticipate being tickled and they'll have the same response. Is that right?

SI: Yes. The new finding of my study is that we found a neural basis — the brain region which responds to tickling. So these neurons also respond to anticipatory tickling. So I just put my hand in front of them, and move my fingers as if I'm going to tickle them, and they already feel ticklish. And they start vocalizing, and they chase my hand really fast. So this we call "play behaviour".

CO: Well, you see this in children, don't you — when you can come toward them as though you going to tickle them, and they'll burst into hysterical laughing about it.

SI: Right. That's what we saw also in rats.

(Shimpei Ishiyama)

CO: What does this tell you about tickling?

SI: So from these results, we got to know that tickling is pretty much related to play behaviour, because the neurons that are activated by tickling can be also activated by the play behaviour, in the same manner. So this is a pretty important finding, because your play behaviour is known to be very important for developing normal cognitive capacity — social-cognitive capacity. And so without that play — if you deprive play behaviour, for example, in rats — they become socially incapable when they're old.

CO: This would be true, I guess of all animals. And humans.

SI: Yes. And that's why we thought ticklishness is somehow the brain's trick to make us play more, or have fun more.

For more on this story, listen to the full interview with Shimpei Ishiyama.

(Shimpei Ishiyama)

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